Handbook of Pediatric Neurosurgery

situation in children is more complex, and emboli-
zation is rarely used as a stand-alone modality, as
the recurrence rate is higher and lesion immaturity
may preclude complete visualization angiographi-
cally. Regardless, embolization is a significant aid in
the treatment of AVMs, reducing their blood supply
and facilitating operative approaches (usually <72
hours before surgery). Embolization also has a role
in targeted treatment of nonoperative lesions, by
occluding areas at risk of hemorrhage such as
aneurysms or high-risk varices (those that are
intraventricular).
25.5 Surgical Technique
The variability of AVM size, location, and vascular
pedicles makes each case unique. However, there
are general principles able to be applied to all AVM
surgical cases. Approaches should be selected to
maximize access to the lesion, avoid eloquent neu-
rologic cortex (if possible), and a ord the surgeon
visualization of feeding and draining vessels to
permit proximal control of blood flow.
25.5.1 Preoperative Preparation
Communication with nursing and anesthesia
before the case will streamline care. In general,
equipment should include an operating micro-
scope, multiple suctions, a craniotome, bipolar
electrocautery (nonstick, if available), AVM/aneur-
ysm clips, and a retraction system. The anesthesia
team should prepare with multiple large-bore
intravenous catheters and attempt to have blood
products in the operating room. It is good practice
to have the microscope draped and clips selected
prior to opening the incision, in order to be pre-
pared for emergencies.
Operative approach: Frameless stereotaxy can
aid in operative planning, ensuring a wide opening
with full access to AVM vessels and good visualiza-
tion. Ultrasound can help with localization using
real-time imaging. During the craniotomy, care
should be taken to avoid tearing the dura and sub-
jacent vessels. Once open, a clear strategy should
be outlined prior to attacking the lesion. Progres-
sion from feeding arteries to draining veins is
critical, as is avoidance of entering the nidus if
possible ( Fig. 25.3). Repeated inspection of the
surgical field is helpful to ensure that no compres-
sion of draining veins exists. Detailed examination
of the operative bed after completion is key to
avoiding inadvertent residual lesion, as is periope-
rative imaging if possible.
25.6 Complications
● Bleeding is the most immediate complication of
surgery, and risks are magnified in smaller
children, who have little reserve. The loss of one-
quarter of blood volume can induce shock and
there may be rapid decompensation in children,
which mandates careful monitoring and
replacement of blood products by the operative
team.
● Normal perfusion pressure breakthrough is a
phenomenon that is thought to occur after
resection of high-flow AVMs in which the blood
previously transmitted through the AVM is
redirected to smaller, normal vasculature after
the AVM has been removed, with subsequent
inability of the vessels to handle the increased
flow. This can result in brain swelling, increased
intracranial pressure, seizure, neurologic
dysfunction, or hemorrhage. The problem may
be minimized by staged preoperative
embolization and rigorous blood pressure
control postoperatively.
● Neurologic deficit can occur following AVM
resection, although specific rates are hard to
derive, given the wide variability in AVM size
and location.
Fig. 25.3 Intraoperative image of AVM. Intraoperative
photograph demonstrates appearance of AVM on the
surface of the brain. Note the dilated, abnormal vessels
extending up to the sulcal border (white arrowhead).
This lesion had been treated with preoperative embo-
lization, and the intra-arterial embolic agent is black
(Onyx) and can be seen occluding a feeder at the
anterior margin of the lesion (green arrowhead).
Cerebrovascular Disorders
208

Overall, there is low postoperative morbidity in
low-grade (I–III) Spetzler–Martin lesions (ranging
from 0 to 12%), along with a high rate of complete
obliteration (up to 100%), suggesting that surgical
resection of these lesions is warranted, especially
when performed in experienced centers.20,31,39,40
25.7 Postoperative Care and
Follow-up
Immediate postoperative care centers on hemody-
namic stability with good blood pressure control
(keeping the patient normotensive to sometimes
slightly hypotensive, in order to avoid reperfusion
hemorrhage). In general, most patients will spend
a period of time in the intensive care unit and then
often mobilize to the wards. Follow-up will fre-
quently consist of an o ce visit about 1 month
postoperatively and then annually thereafter. In
addition to the perioperative angiogram to con-
firm obliteration of the AVM, an MRI/magnetic res-
onance angiography (MRA) at 6 months may be
helpful as a baseline study, to be compared to sub-
sequent annual MRI/MRA. Imaging is performed
annually for 5 years, if feasible. An angiogram
(DSA) is often performed at 1 year postoperatively
to confirm durable cure.
25.8 Outcomes
In pediatric patients with grade I to III Spetzler–
Martin AVMs treated by resection,40 good recovery
was achieved in 90% and deaths occurred at a rate
of 5%. Radiographic obliteration rates were 89%.
These data strongly support resection as a primary
treatment for patients with Spetzler–Martin grade
I or II AVM. The low postoperative morbidity in
children with these lesions (ranging from 0 to
12%), along with a high rate of complete oblitera-
tion (up to 100%), suggests that delayed control,
inherent to radiosurgery, might not be war-
ranted.20,31,39,40
For comparison, a similar group of patients
treated with radiosurgery alone had a reported
80% e cacy of lesion obliteration at 36 months,
with 4 out of 53 patients having recurrent hemor-
rhage posttreatment.41 One large pediatric AVM
study included 40 patients and confirmed radio-
graphic obliteration of the AVM nidus in 35%
of the patients.42 The cumulative posttreatment
hemorrhage rate was 3.2% per patient per year in
the first year and 4.3% per patient per year over
the first 3 years.42 These rates of obliteration,
which are notably lower than that reported in the
adult population, were potentially complicated by
a slightly larger than average size of treated AVM
in the study group. In contrast, when a group of 53
pediatric patients was stratified by AVM size (<3,
3–10, and >10 mL), in the smallest and middle
group, obliteration rates of 80 and 64.7% were
reported.41
25.9 Surgical Pearls
● Always obliterate feeding arteries before
occluding or dividing draining veins, as
hemorrhage can result if outflow is interrupted
while blood is still entering the AVM.
● Avoid entering the body of the nidus, trying
instead to work circumferentially around the
lesion. If bleeding occurs, it is important to note
that AVM vessels often do not coagulate well due
to their dysplastic nature. Consequently, it is
usually better to cover the area with a small
square of Gelfoam and compress gently rather
than to dive into the nidus with bipolar
electrocautery.
● It is good practice to periodically zoom out and
inspect the surface of the brain for unexpected
bleeding or swelling. Misplaced retractors or
compression of draining veins can cause
problems if unrecognized.
● Careful examination of the resection cavity at
the completion of the surgery is important to
reduce the risk of missing residual nidus.
● If possible, perioperative imaging (particularly
with DSA) can help ensure complete resection
and minimize the possibility of postoperative
hemorrhage from residual AVM.
25.10 Common Clinical
Questions
1. What are the outcomes associated with the
di erent Spetzler–Martin grades?
2. What sort of outcomes can be expected for
more complex, large AVMs treated with
multimodality therapies?
3. What considerations should be reviewed in the
setting of a patient diagnosed with an AVM who
is pregnant?
4. What steps are helpful in the immediate
management of a child presenting with a
hemorrhage from an AVM?
Arteriovenous Malformations
209

25.11 Answers to Common
Clinical Questions
1. For patients treated operatively, outcomes can
be predicted by the Spetzler–Martin grade.
Grade I had 0% deficits, grade II had 5% deficits,
grade III had 16% deficits, grade IV had 27%
deficits, and grade V had 31% deficits.34 Looking
specifically at children, a more recent report
describes an 89% radiographic obliteration rate
and 5% morbidity and 5% mortality rate for
grade I to III lesions.40
2. The e cacy of multimodality treatment of
large, complex lesions is supported by a group
of 53 children at a 3-year follow-up in whom a
58% cure rate was noted for AVMs greater than
6 cm in diameter.43
3. Treatment of a known AVM should be
undertaken prior to pregnancy, whenever
possible. There are rare situations of
documented intracranial AVM in a pregnancy.
Either the AVM was not addressed prior to
gestation or neurological sequelae led to its
discovery. Data in this small group of patients
are inconclusive, particularly with regard to the
rate of hemorrhage during the pregnancy.44,45,
46,47,48,49,50 MRI is safe for initial evaluation of
the anatomy of the lesion.51 No specific
recommendations can be made if the AVM is
diagnosed during pregnancy, because individual
risk–benefit relationships need to be assessed. If
the mother has an untreated or partially treated
AVM, caesarean section should be considered.40,
48,50,52
4. The following steps are warranted for the child
who presents with an intracranial hemorrhage.
It is important to note that severity of
presentation can vary greatly and thus
treatment has to be individually tailored. If a
child presents with an intraparenchymal
hemorrhage without a clear etiology on initial
evaluation, AVM should be considered and a CT
angiogram (CTA) may be helpful in the acute
setting to identify the presence of dilated
vessels or nidus. (If no clear lesion is found,
repeat imaging in 4–6 weeks with MRI should
be performed to evaluate the hemorrhage
cavity after the clot has cleared.)
● Access: Large-bore intravenous (at least two),
arterial line, bladder catheter (airway
intubation if unable to protect airway), and
nasogastric tube if intubated.
● Blood pressure control (labetalol or Nipride)
with goal of normotension for age.
● Intracranial pressure control—external
ventricular drain if hydrocephalus (Note:
avoid overdrainage of CSF to prevent re-
rupture, often no more than 5 mL at a time),
head of bed (HOB) elevated.
● Antiepileptic medication if concern for
seizure.
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Cerebrovascular Disorders
212

26 Pediatric Cavernous Malformations
Rajiv R. Iyer, Mari L. Groves, Nir Shimony, George I. Jallo
26.1 Introduction/
Epidemiology
Cavernous malformations (CMs), also referred to
as cavernous angiomas, or cavernomas, occur
throughout the central nervous system (CNS) and
are angiographically occult vascular lesions made
up of closely packed thin-walled sinusoidal vessels
without interspersed neural tissue. The majority of
CMs are supratentorial, but infratentorial and
intraspinal lesions are also known to occur.1,2 In
the pediatric population, CMs can cause significant
morbidity manifesting in the form of headaches or
seizures, as well as acute hemorrhage causing
more severe neurological decline. CMs have been
reported to occur in 0.4 to 0.5% of the general pop-
ulation and are more common in adults, while
approximately 25% occur in the pediatric age
group.3,4,5,6 There is no clear gender predilection
associated. The majority of CMs in the pediatric
population are solitary and sporadic. However,
those with multiple CMs, or in patients with a pos-
itive family history, a high index of suspicion
should be maintained for an inherited form of this
disorder.7 Familial forms of this disorder demon-
strate autosomal dominant inheritance and are
caused by genetic mutations in the CCM1, CCM2,
and CCM3 genes on chromosomes 7q, 7p, and 3q,
respectively.8,9,10,11,12 In patients found to have an
intraspinal CM, there is thought to be an increased
risk of harboring other CMs within the neuraxis,
warranting radiographic screening.13 Risk factors
for the development of CMs are not well under-
stood, but may include prior radiation therapy or
the presence of venous anomalies.14,15,16,17,18
26.2 Pathology
Macroscopically, CMs are well-circumscribed,
lobulated lesions separated from neural paren-
chyma that have a “mulberrylike,” purplish
appearance due to the presence of partial throm-
bosis and a low rate of blood flow through the
vascular channels within (Fig. 26.1a). The imme-
diately surrounding brain or spinal cord paren-
chyma may be gliotic due to chronic inflammation
and often contains hemosiderin staining from
prior hemorrhage. Histologically, CMs consist of
densely packed sinusoidal vessels lined by a thin
layer of endothelium embedded in a collagenlike
stroma. The tight junction barrier of this endothe-
lium, however, has increased permeability due in
part to a lack of astrocyte foot processes.19 The
blood vessels of CMs are also devoid of smooth
muscle, pericytes, and other properties of mature
endothelium, and typically demonstrate hyaliniza-
tion (Fig. 26.1b). For these reasons, there is
thought to be recurrent red blood cell extravasa-
tion and resultant microhemorrhages of di erent
ages. Varying degrees of calcification may also be
present.
26.3 Diagnostic Imaging
In contrast with CNS vascular lesions such as arte-
riovenous malformations, arteriovenous fistulas,
and aneurysms, CMs are typically undetectable on
cerebral angiography and are thus classified as
angiographically occult.20,21 These lesions are fre-
quently asymptomatic and have been increasingly
detected in an incidental manner with the
Fig. 26.1 (a) Gross appearance of cav-
ernous malformation demonstrating
“mulberrylike” appearance caused by
concurrent thrombosis and low blood
flow through the lesion. (b) Photo-
micrograph of a CM demonstrating
closely interspersed sinusoidal chan-
nels and red blood cell extravasation.
213

widespread use of magnetic resonance imaging
(MRI).22 In the acute setting, computed tomogra-
phy (CT) imaging serves a use in detecting acute
hemorrhage and large lesions; however, MRI
remains the most sensitive study for the detection
of CMs.23,24 In fact, early studies demonstrated that
CT imaging detected only approximately 36% of
CMs that were evident on MRI.7 Zabramski and
colleagues in 1994 described a classification sys-
tem for CMs based on their imaging characteris-
tics. Type I lesions are characterized by subacute
hemorrhage as evidenced by hyperintensity on
T1-weighted imaging and a quick transformation
from a hyper- to hypointense lesion on T2-
weighted MRI. Type II lesions demonstrate concur-
rent hemorrhage and thrombosis, correlating with
the underlying pattern of repeating hemorrhage
and clotting over time. These lesions feature a
reticulated pattern of high and low signal intensity
at their core, surrounded by a hypointense rim on
T2-weighted imaging that corresponds to circum-
ferential hemosiderin deposition, with a classic
“popcornlike” appearance on MRI (Fig. 26.2).
Type III lesions contain chronic hemosiderin depo-
sition, while type IV CMs are punctate and easier
to detect with gradient echo (GRE) sequences, and
histopathologically may be considered capillary
telangiectasias.25 Compared to T2-weighted fast
spin-echo sequences, T2-weighted GRE sequences
are better at detecting chronic hemosiderin depo-
sition and deoxyhemoglobin. Especially relevant
for familial cases of CMs, susceptibility-weighted
imaging has been thought to have an even higher
sensitivity than T2-weighted imaging for detection
of small CMs.26 CMs typically demonstrate mini-
mal, if any, enhancement following administration
of gadolinium. An association exists between CMs
and the coexistence of a developmental venous
anomaly (DVA). This association has been reported
to be approximately 20%, and in the majority of
hemorrhagic cases leading to the diagnosis of a
DVA on imaging, an associated CM was present at
the location of hemorrhage.18,27
26.4 Clinical Presentation
26.4.1 Intracranial CMs
Similar to the adult population, the majority of
CMs in the pediatric population are supratentorial
in location, while approximately 20% are infraten-
torial.28,29 The average age at presentation has
been reported to be around 10 years, although
they can arise at any point from neonatal stages,
throughout adolescence and into adulthood.28,29,30,
31,32 Supratentorial CMs generally occur in the
cortical regions and subcortical white matter, but
in other rare circumstances are found in deeper
locations such as the basal ganglia, hypothalamus,
ventricular system, optic chiasm, pineal region,
and others.28,33
In young children without a family history,
asymptomatic identification of CMs is generally
uncommon. When symptoms do arise, they are
attributable to hemorrhage. This can be subdivided
into chronic microhemorrhages that cause sur-
rounding parenchymal edema and irritation over
time, and large intralesional or intraparenchymal
hemorrhages that cause acute neurological deficits
or deterioration. For many children with supraten-
torial CMs, their primary presentation is with seiz-
ures.28,31,34 In other patients, medical attention is
sought due to headaches or neurological deficit.
Repeated hemorrhages in certain patients can
cause progressive CM growth and associated mass
e ect; these individuals may present from signs of
Fig. 26.2 (a) T2-weighted magnetic
resonance image (MRI) demonstrating
left frontal precentral gyrus CM exhib-
iting a reticulated core of hypo- and
hyperintensity and a T2-hypointense
surrounding rim. (b) T2-weighted MRI
demonstrating left midbrain and cer-
ebral peduncle CM in a 14-year-old girl
who presented with pupillary dilation.
Cerebrovascular Disorders
214

elevated intracranial pressure or focal neurological
deficit.
Infratentorial CMs consist primarily of brainstem
and cerebellar lesions. Patients with brainstem CMs
may exhibit a myriad of signs and symptoms
including cranial nerve deficits, sensory disturban-
ces, hemiparesis, altered level of consciousness, and
hydrocephalus.35 Acute or progressive headaches
that localize to the occipital region, cerebellar dys-
function, and, less commonly, cranial nerve palsies
or acute neurological decline are some of the clini-
cal signs and symptoms associated specifically with
cerebellar CMs.36,37 In the pediatric population, due
to the relatively high incidence of posterior fossa
tumors, lesion characteristics such as an associated
venous anomaly or the presence of blood of di er-
ent ages should lead the clinician to maintain a
higher index of suspicion for CMs. However, given
the high incidence in children of primary brain
tumors in the posterior fossa, a di erential diagno-
sis must be maintained.
26.4.2 Intraspinal CMs
Intraspinal CMs comprise about 5% or less of all
pediatric CMs a ecting the neuraxis.29 These lesions
can be classified as intramedullary, intradural extra-
medullary, and extradural, with intramedullary
CMs being the predominant subtype. Given the rar-
ity of these lesions, the literature describing their
typical presentation and guiding their clinical ma-
nagement is limited to scattered case reports and
small case series.38,39,40,41,42,43 Although rare, intra-
spinal CMs can lead to significant morbidity given
the high density of functionally critical neural tissue
that lies adjacent. Commonly, patients will present
with neck or back pain, sensory disturbances such
as paresthesias or frank numbness, and motor
weakness, myelopathy, and bowel or bladder dys-
function. Any constellation of these symptoms in a
child should raise the suspicion of an intramedul-
lary lesion such as a CM. Importantly, patients with
intraspinal CMs should undergo pan-neuraxis imag-
ing to rule out the presence of other such lesions,
as there is a higher prevalence of coexisting CMs in
these patients.39,44
26.5 Natural History
Several studies have attempted to elucidate the
natural history of CMs in the adult population in
order to help clinicians define their hemorrhagic
risk and to guide clinical management following
diagnosis. Rates of hemorrhage are typically
defined as either events per lesion-year or events
per person-year, and have been reported to be
between 0.7 and 22.9%.25,45,46,47,48,49,50 Unfortu-
nately, these studies are heterogeneous with
respect to the amount of familial CM cases as well
as the number of truly asymptomatic patients they
contain. One consensus feature of these studies,
however, is that prior CM hemorrhage itself con-
fers risk for subsequent hemorrhage.
In the pediatric population, there are substan-
tially less data shedding light on the natural
history of CMs. In 2012, Al-Holou and colleagues
evaluated over 14,000 patients under the age of
25 years who underwent MRI of the brain and
found 164 CMs in 92 patients, 42% of whom were
asymptomatic. At follow-up, the authors discov-
ered a hemorrhage rate of 1.6% per patient-year
and 0.9% per lesion-year in the group of patients
with incidentally discovered CMs. Similar to
reports in the adult population, for those patients
who at some point presented with acute neurolog-
ical symptoms, the hemorrhage rate was higher at
8% per patient-year. Importantly, factors associated
with a higher hemorrhagic rate included an infra-
tentorial location, consistent with previous reports,
as well as the presence of a DVA.51,52
More recently, Gross and colleagues evaluated a
cohort of 167 pediatric patients (younger than 21
years) with CMs, 26% of whose lesions were inci-
dentally discovered. Overall annual hemorrhage
rate was determined to be 3.3% per lesion-year,
and 1.2% in subgroup analysis of solitary, inciden-
tal CMs. Overall hemorrhage rate was determined
to be 11.3% for previously hemorrhagic lesions.
Importantly, of 11 untreated hemorrhagic CMs
with greater than 5-year follow-up, temporal rela-
tion to prior hemorrhage played a role in subse-
quent hemorrhage risk: annual hemorrhage rates
were 18% within 3 years of prior CM hemorrhage,
decreasing to 4.8 and 3.3% at 3 and 5 years of
respective follow-up. This temporal clustering of
CM hemorrhages has been previously reported.53
Overall, multivariate analysis of their cohort
yielded risk factors for CM hemorrhage that
included prior hemorrhage, associated DVAs, and a
brainstem location.31
26.6 Surgical Indications,
Techniques, and Outcomes
Pediatric patients with neuraxis CMs represent a
heterogeneous group with varying age, presenta-
tion, and number of lesions. Given these variables,
Pediatric Cavernous Malformations
215

treatment options must be tailored for each
patient and each clinical scenario encountered. As
the natural history of CMs in the pediatric popula-
tion becomes better defined, surgical indications
also become elucidated. In asymptomatic patients
with incidentally discovered CMs, and especially
those with higher-risk, deep-seated lesions,
expectant observation is appropriate with serial
imaging over time to monitor lesion growth or
clinically silent hemorrhage.54,55 For symptomatic
patients, surgical excision is the mainstay of treat-
ment, as children have a longer time course to
develop progression of clinical symptoms from le-
sion growth or repeated hemorrhage over time.
Like other clinical decisions in the pediatric popu-
lation, the risks and benefits of action and inaction
must be weighed for those patients with CMs.
Generally, in children, an aggressive treatment
strategy involving surgical excision is undertaken
when lesions are safely accessible, symptomatic, or
demonstrate evidence of current or prior hemor-
rhage.32 This is especially true for easily accessible
supratentorial lesions in noneloquent regions. For
deep-seated lesions, such as thalamic or brainstem
CMs, or those in eloquent cortex, management is
more controversial and surgical morbidity must be
weighed against the benefit of resection. A pattern
of repeated hemorrhage or progressive neurologi-
cal deficit due to mass e ect may indicate surgical
intervention for such CMs.56,57 For brainstem CMs,
exophytic lesions and those that come to the pial
surface are more appropriate for surgical interven-
tion, as these features minimize the chance of
harm to normal neural tissue. Appropriate surgical
planning must include a thorough knowledge of
the vital structures in the vicinity of the lesion,
including white matter tracts that are intolerant to
retraction, brainstem nuclei, perforating vessels,
and draining veins. Morbidity in these cases may
result from incomplete CM resection and hema-
toma formation.56
In those patients who present with a neurological
deficit due to an acutely hemorrhagic CM, acute
decline due to elevated intracranial pressure and
mass e ect may warrant immediate intervention.
Typically, however, these lesions are managed ini-
tially with supportive therapy and rehabilitation fol-
lowing the initial hemorrhagic event. Weeks later,
after swelling and edema have subsided, excision
can be performed to prevent further morbidity due
to repeat hemorrhages that have been shown to
temporally cluster after the initial event.53
Surgical intervention is often employed for
children who present with medically refractory
seizures due to supratentorial CMs. It is important
that seizure semiology localizes to the lesion,
which in some cases may require EEG (electroen-
cephalographic) monitoring. In patients with mul-
tiple CMs, it is especially important to discern
which lesion may be symptomatic prior to surgery.
For those who undergo surgery for CM-induced
epilepsy, improved seizure control postoperatively
can generally be expected. In some cases, continued
medical therapy is required to prevent seizures
postoperatively, while, in others, doses can be
weaned.33,58 Some studies have suggested that exci-
sion of surrounding hemosiderin-stained neural
parenchyma may improve seizure control postoper-
atively.59,60 Others, however, suggest that good seiz-
ure control can result without the need for such
extensive resections.33,61 Therefore, when undertak-
ing CM resection for medically refractory epilepsy,
more extensive surgery may decrease the likelihood
of postoperative seizures, but caution should be
used in lesions that are adjacent to or within func-
tionally relevant areas so as to not cause iatrogenic
deficits due to resection of nonlesional tissue.28
Surgical excision often utilizes the safest and
most direct approach to the target lesion with the
intent of leaving functional cortex and other
deeper, vital structures unharmed. Under close
neurophysiological monitoring, resection of the
CM is often best accomplished by circumferentially
dissecting the lesion away from adjacent neural
parenchyma. Generally, entering the CM during
resection is inadvisable, as it can lead to di cult-
to-control bleeding and may risk incomplete
resection. However, in some cases of deep cortical
lesions and brainstem CMs, dissection along the
periphery of the lesion is not possible without
causing retraction injury to functionally critical
surrounding structures and may thus warrant
piecemeal resection and internal debulking. Typi-
cally, if a DVA is encountered, this is preserved.
Meticulous hemostasis is critical following CM
resection and careful inspection of the resection
cavity helps avoid remnant lesion, which can lead
to lesion recurrence or repeat hemorrhage.
Surgery is often well tolerated in children with
CMs. Several series over the recent decades
describe the international experience with CMs in
the pediatric population.28,29,32,33,55,62 Overall mor-
tality rates are very low and are commonly 0%. The
majority of reports consist primarily of supraten-
torial CMs with outcomes often reported as good
or excellent. Cerebellar CMs in the pediatric popula-
tion have also been shown to have excellent
surgical outcomes with low morbidity and mortal-
Cerebrovascular Disorders
216

ity.37 Not surprisingly, deep-seated CMs, including
brainstem CMs, demonstrate a higher rate of post-
operative morbidity. These rates have been reported
to be approximately 12 to 30%.35,56 In many cases of
brainstem CMs, transient neurological deficits are
seen postoperatively, which tend to improve over
time. However, permanent neurological injury is
also possible. Overall, brainstem CM surgery in the
pediatric population is well tolerated, and the
higher rate of morbidity for these lesions empha-
sizes the importance of choosing appropriate surgi-
cal candidates after weighing the risks and benefits
of intervention, as well as the safest surgical
approach for lesion resection.63,64
Intramedullary CMs are rare in children but are
often managed surgically due to the risk of intra-
medullary hemorrhage and progressive myelop-
athy over time. With simple laminectomy and
intradural exploration, these lesions can be
resected under electrophysiological guidance with
maintenance of preoperative function and possible
neurological improvement over time.39
26.7 Radiosurgery
The role of radiosurgery is a highly debated topic
in the management of CMs. There are little data
supporting its use as a first-line therapy in the
pediatric population. Various reports suggest a
decrease in hemorrhage rates following radiosur-
gery, but it has been suggested that these studies
demonstrate an unusually high pretreatment
hemorrhage rate.35 Within 2 to 3 years of radiosur-
gery, rates of hemorrhage are reported to be
between 8.8 and 32%. However, after this time
period, hemorrhage rates appear to drop to 1.1 to
4.5%. Rates of morbidity including neurological
deficit following radiosurgery have been reported
to be between 13 and 26%.65,66,67,68 Overall, it
remains to be determined whether hemorrhage
rates following radiosurgery di er significantly
from the natural history of these lesions in the
pediatric population. For children, first-line ther-
apy should be surgery for symptomatic lesions,
while the role of radiosurgery as opposed to obser-
vation alone for inaccessible lesions or poor surgi-
cal candidates requires further elucidation.
26.8 Common Clinical
Questions
1. In what locations do CMs occur in the pediatric
population and what are some risk factors
associated with hem orrhage?
2. What are the common presenting symptoms for
children with CMs?
3. What is the recommended treatment strategy
for symptomatic supratentorial and
infratentorial CMs?
26.9 Answers to Common
Clinical Questions
1. In children, the most common location for CMs
is in the supratentorial compartment. As many
as 80% of lesions are found in the cerebrum.
Other areas where one may find these lesions
are in the infratentorial compartment, which
can be subdivided into cerebellar CMs and
brainstem CMs. Intraspinal CMs are rare but,
when encountered, are typically intramedullary
in location. Suggested risk factors for
hemorrhage include prior hemorrhage, an
infratentorial location, and the presence of a
DVA.
2. The most common presenting symptom for CMs
in children is seizures. Other symptoms depend
on lesion location and the temporal acuity of
hemorrhage. With chronic, repeated
hemorrhages, seizures and headaches are
possible, and if hemorrhage is acute, symptoms
from elevated intracranial pressure or mass
e ect can occur, including focal neurological
deficits. Cerebellar dysfunction, cranial nerve
palsies, and hydrocephalus are possible with
infratentorial lesions. Intraspinal lesions can
present with motor weakness, sensory
disturbances, or chronic myelopathy due to
hemosiderin irritation and gliosis surrounding
the lesion.
3. Observation with serial imaging is often
employed for asymptomatic lesions found in
children. Overall, however, an aggressive
treatment approach is used in children with
CMs to prevent morbidity later in life. Surgical
treatment is the therapeutic mainstay for
symptomatic lesions that are surgically
accessible and demonstrate evidence of current
or prior hemorrhage. Resection of the
hemosiderin rim for cases of medically
refractory epilepsy can help decrease the
likelihood of postoperative seizures, but this
method should be limited to noneloquent
cortical areas. Symptomatic cerebellar lesions
can be surgically removed with good results.
Brainstem lesions that are exophytic or lie in
close proximity to a pial surface are better
suited for surgical intervention. Repeated
Pediatric Cavernous Malformations
217

hemorrhages and progressive neurological
deficit are reasons to consider surgical
intervention for brainstem CMs.
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Pediatric Cavernous Malformations
219

(Trang không có chữ)

VI
Section VI
Developmental and
Congenital Cranial Disorders
27 Chiari Malformations

222
28 Encephaloceles

229
29 Congenital Arachnoid Cysts

242
30 Neuroenteric Cysts

253
31 Intracranial Lipomas

256
32 The Dandy–Walker
Malformation: Disorders of
Cerebellar Development and
Their Management

261
33 Craniosynostosis

264
34 Management of Craniofacial
Syndromes

276
35 Germinal Matrix Hemorrhage
in Premature Infants

288
36 Surgical Management of
Hydrocephalus

297
37 Treatment of Hydrocephalus
in the Developing World

305

27 Chiari Malformations
Karl F. Kothbauer
27.1 Introduction
What is today called Chiari I malformation was
originally described in 1891.1 It is a developmental
anomaly of the hindbrain. Herniation of the cere-
bellar tonsils through the foramen magnum into
the cervical spinal canal is its primary feature.
Four types of Chiari malformation are described2:
1. Chiari I (also known as cerebellar ectopia) is
defined as the caudal displacement of the
cerebellar tonsils below the level of the
foramen magnum with obliteration of the
cisterna.
2. Chiari II (also known as Arnold–Chiari
malformation)3 is a more severe and extensive
hindbrain anomaly with caudal displacement of
brainstem, cerebellar tonsils, vermis, posterior
inferior cerebellar arteries (PICAs), and the
fourth ventricle. It often includes a
cervicomedullary kink and cranially directed
cranial nerve roots. Brainstem dysfunction is a
typical finding. Chiari II occurs with
myelomeningocele and hydrocephalus,
and frequently is associated with
syringomyelia.4
3. Chiari III consists of herniation of the posterior
fossa contents into an occipitocervical
encephalomeningocele. It also includes a
cervical spina bifida. Chiari III is the severest
form of the Chiari complex5 and is considered
incompatible with survival.
4. Chiari IV is the rarest and mildest form. It is
characterized by cerebellar hypoplasia, but no
herniation.5
Sometimes a transitional form of Chiari I malfor-
mation with morphological signs of brainstem
dysplasia but without spina bifida is referred to as
Chiari 1.5.5 This transitional form is regarded as
Chiari I malformation in the present context.
Syringomyelia (also known as hydromyelia), the
formation of a longitudinal cavity within the spinal
cord, is present in about 50 to 70% of the patients
with Chiari I malformation 6,7 and in up to 95% of
patients with Chiari II.4,8,9
Many attempts to explain the syrinx formation
have been made. Gardner and Angel postulated a
delayed and incomplete embryonic closing of the
central canal with an (at least potentially) open
communication from the fourth ventricle into the
central canal of the spinal cord. In his hydrody-
namic theory, he suggested that the extension of
the syrinx cavity is caused by a “water hammer”
e ect, i.e., a pulsatile transmission of the cerebro-
spinal fluid (CSF) from the fourth ventricle into the
central canal.10
Later, Williams modified this theory to the “cra-
niospinal pressure dissociation hypothesis,”11
where the craniospinal pressure di erences due to
venous pulsations, rather than Gardner arterial
pulse waves, were put forward as the primary
mechanism responsible for the syrinx formation.
In 1994, Oldfield et al12 used dynamic magnetic
resonance imaging (MRI) to study the pulsatile
movement of the CSF in the posterior fossa and
the cervical spinal canal before and after decom-
pressive surgery. This newer concept suggests that
the obstruction at the foramen magnum caused by
crowding of the tonsils results in a block of the CSF
flow during systole. This causes a systolic wave in
the spinal CSF that acts on the surface of the spinal
cord. This results in progression of syringomyelia
by repeated compression of the cord, probably by
mechanical disruption of the cord tissue with
every pressure wave, and by forcing fluid into the
cord from the outside in. It has been suggested
that the pulsatile pressure waves force CSF into the
cord through the perivascular and interstitial
spaces. In addition, the syrinx fluid is propelled
longitudinally within the syrinx during each car-
diac cycle. This together may be responsible for the
origin and persistence of syringomyelia. Armonda
et al13 showed the changes in pulsatile CSF flow
before and after posterior fossa decompression.
Based on these pathophysiological concepts, a
full array of surgical strategies has been advo-
cated in the treatment of Chiari I m alformation
and syringomyelia. The comm on denom inator of
all these strategies is posterior craniovertebral
decompression. There is little controversy about this
principle. However, the details of the procedure, its
extent and invasiveness, and the technique of dural
closure are subject to considerable debate.
27.2 Anatomy
As a group of developmental disorders, Chiari
malformations are characterized by an abnormal
anatomy of the structures of the craniocervical
222

junction. Usually, this involves only the intradural
structures, but it may also be associated with a
degree of abnorm ality of the osteoarticular appa-
ratus of the craniocervical junction.
Intradural anatomy. The normal location of the
cerebellar tonsils and the presence and size of the
cisterna magna are the primary anatomical struc-
tures changed in Chiari. The cerebellar tonsils are
dislocated caudally into the cervical spinal canal to
a varying degree. Usually, displacement of at least
a few millimeters (>3 mm) below the level of the
foramen magnum is required to call the finding
“Chiari.” Absence or very small size of the cisterna
magna appears more physiologically relevant.
Descent of the tonsils below the level of the C2
vertebral arch is not infrequent.
Anatomical changes in Chiari II malformation
are more extensive, with more structures to be
caudally dislocated, such as the vermis and the
lower brainstem. In addition, a medullary kink
may be present and the caudal cranial nerves may
have an upward course.
Chiari II is more often associated with bony
abnormalities than Chiari I. These abnormalities
include primarily an elevation of the dens with a
ventral indentation of the brainstem. Occipitaliza-
tion of the atlas, a bifid posterior atlas arch, and an
occipital bony keel with far ventral indentation
may occur.
27.3 Clinical Findings
Not infrequently in the era of MRI, Chiari I malfor-
mation is an incidental finding, discovered, for
instance, in the course of evaluation after trauma.
A correlation between general symptoms such as
headache and the presence of Chiari must be care-
fully evaluated.
The variety of presenting symptoms of Chiari I
malformation is shown in Box 27.1 and does
include headaches. Clinical findings upon exami-
nation are equally diverse, as they include poten-
tial dysfunction of all systems located in and
traversing the craniocervical junction (Box 27.2).
Characteristically, if neurological dysfunction is
found, three syndromes are defined in Chiari mal-
formation.14
1. Foramen magnum syndrome (20%): headaches
in about one-third of patients, ataxia,
corticospinal and sensory deficits, cerebellar
signs, and lower cranial nerve dysfunction, such
as swallowing di culties or nasal speech.
2. Central cord syndrom e (60%):
characteristically associated with
syringomyelia. Dissociated sensory loss, lower
m otor neuron syndrom e with m uscle
atrophy, and pyram idal signs.
3. Cerebellar syndrome (10%): ataxia, nystagmus,
dysarthria.
Box 27.1 Symptoms of Chiari I
malformation
● Pain
● Headache
● Neck pain
● Shoulder pain
● Arm pain
● Facial pain
● Diplopia
● Numbness
● Weakness
● Tinnitus
● Nasal speech
● Dizziness
● Hearing loss
● Hiccup
Box 27.2 Clinical findings of Chiari I
malformation
● Hyperreflexia
● Nystagmus
● Gait disturbance
● Hand muscle atrophy
● Cape sensory loss
● Ataxia
● Oculomotor disturbance
● Lower cranial nerve dysfunction
● Babinski’s sign
27.4 Diagnostic Evaluation
Imaging with MRI is the hallmark of modern diag-
nosis in this condition. All other imaging modal-
ities may be required here and there under certain
conditions, but not regularly. MRI shows all neces-
sary anatomical changes which constitute the
diagnosis of Chiari malformations and those that
are required to make therapeutic decisions, as well
Chiari Malformations
223

as those that are needed for surgical planning. This
includes particularly syringomyelia (Fig. 27.1).
Computed tomography (CT) may sometimes be
necessary to assess the bone situation at the cra-
niovertebral junction. The MRI findings for Chiari
malformation are defined in the anatomical
description. The specific findings on imaging for
Chiari II malformation are listed in Box 27.3.2
Box 27.3 Anatomic imaging findings
in Chiari II malformation
● Bend deformity of medulla
● Tectal fusion (tectal beaking)
● Enlarged interthalamic adhesion
● Elongation of medulla
● Low attachment of tentorium
● Steep sinus rectus
● Hydrocephalus
● Syringomyelia
● Trapped fourth ventricle
● Cerebellomedullary compression
● Agenesis of corpus callosum
● Microgyria
● Platybasia
27.5 Nonsurgical Management
There is no nonsurgical treatment for this condi-
tion. The decision whether or not to perform sur-
gery depends on the symptoms, the extent of the
anatomical abnormality, and, in particular, the
presence of significant structural damage such as
syringomyelia.
The natural history of untreated Chiari I malforma-
tion is not well known, but in a larger series ofobserved
cases a relatively benign evolution is suggested.15
27.6 Surgical Indications
The decision for or against surgery must be strictly
viewed from the best interest of the patient. Symp-
toms such as pain that can be reasonably associ-
ated with the pathology should warrant surgery.
“Reasonably associated” may not be so easily
defined, but neck pain and shoulder pain (due to
indentation of cervical nerve roots or compression
of the spinal trigeminal nerve complex) fall in this
category. Neurological dysfunction as in one of the
three syndromes will constitute a surgical indica-
tion. In asymptomatic patients, the presence of
structural tissue damage in the form of syringo-
myelia, even if (yet) asymptomatic, is considered
an indication for surgery. Certainly, a previously
observed patient with newly developed syrinx or
symptoms would also qualify for surgery.
Chiari II malformations are much less frequently
significant for craniocervical crowding, but if they
are, maybe due to cyst formation or bony narrow-
ing, decompression may be indicated as well. Since
most patients with Chiari II are patients with spina
bifida, and the majority of them still have shunted
hydrocephalus, it is imperative to ensure proper
shunt function or patent third ventriculostomy
prior to posterior decompression.
27.7 Surgical Technique
Penfield and Coburn first performed a posterior
fossa decompression in the late 1930s (their first
patient died in the first night after surgery).16
In 1941, Adams et al17 suggested to treat Chiari
malformation with a decompression of the cervical
spinal cord and the cerebellum. Gustafson and
Oldberg already suggested that syringomyelia
might respond to unblocking of the craniospinal
CSF pathways,18 even before Gardner and Angel.10
Fig. 27.1 Significant caudal displace-
ment of the (a) cerebellar tonsils and
(b) cervicothoracic syringomyelia in a
16-year-old girl with Chiari I malfor-
mation who presented with bilateral
fifth nerve palsy.
Developmental and Congenital Cranial Disorders
224

Surgery for Chiari malformation is closely inter-
twined with surgical treatment of the frequently
associated syringomyelia.
The “correct” way to treat Chiari malformations
is one of the most disputed issues in pediatric neu-
rosurgery. The common ground is that a posterior
fossa decompression should be made. Some sug-
gest that this craniectomy must be of considerable
size19; some even combine this with some form of
cranioplasty.20
This author prefers small craniectomies, aimed
at significantly enlarging the foramen magnum.
Some authors advocate that the craniectomy alone
may be su cient,21 while some argue that the
dura must be opened.22 Some try to only open the
dura, but not the arachnoid.23 Interestingly, while
there appear to be a large number of centers
where it is custom practice to microsurgically
shrink the cerebellar tonsils upward, there are
comparatively few reports about this practice.22,24,
25,26
Closure of the dura again is disputed. In the
older literature, the dura was just left open.27
Today, mostly the dura is closed with some form of
graft. Autografts from the fascia lata, pericranium,
or the nuchal ligament were proposed.20,28 Most
report dural closure with an artificial dural substi-
tute,12,28,29 which is also the preference of this
author. The use of fascia lata requires a second
incision at the thigh, which is uncomfortable, and
all autografts carry a significant risk of strong scar
tissue formation, which may in fact obliterate the
CSF spaces at the craniovertebral junction rather
than keep them open.
Many of these technical questions are handled
according to the experience and reflected choice of
the individual surgeon rather than being based on
a scientific consensus or even scientific evidence.
Since di erent choices of surgical technique
nonetheless mostly lead to comparable and favor-
able surgical results and all appear to have a more
or less low complication rate, it may also be argued
that individual patients with individual circum-
stances and anatomical context may benefit from
individual surgical technique choices.
Syringomyelia associated with Chiari malforma-
tion is treated only with craniovertebral decom-
pression. Contrary to prior practice, myelotomy
and placement of a syringosubarachnoid drainage
are considered only in cases with persistent or
progressive syrinx after primary posterior cranio-
vertebral decompression.30
27.8 Complications
Complications after craniovertebral decompres-
sion are rare but do occur, and their prevention
requires adherence to meticulous surgical techni-
que and proper postoperative monitoring. The first
patient reported to have undergone decompres-
sive surgery died from respiratory depression in
the first night after surgery.16
Postoperative respiratory problems may occur
also in modern neurosurgical practice and thus
require proper monitoring at an intensive care unit
(ICU) overnight after surgery. Wound-healing di -
culties, CSF leakage, or subcutaneous collection
may occur. This must be avoided by employing
meticulous surgical technique with duroplasty,
watertight muscle and fascial closure using size 1
absorbable sutures, subcutaneous sutures, and a
running locked skin suture with meticulous adap-
tation of the skin edges. Even a seemingly minor
skin scab after less-than-optimal suture may result
in CSF leakage and a host of subsequent problems
including revision, infection, intracranial hypoten-
sion, and an unhappy family.
Neurological dysfunction after craniovertebral
decompression is very infrequent. Vascular dam-
age to the PICA has been implied and may play a
role, but usually the PICA is well visible and dam-
age to it or excessive manipulation which may
result in local vasospasm must be avoided. This
author has once experienced the development of
significant swelling of the protruding cerebellar
tonsils, which was reflected in significant changes
in intraoperative motor evoked potential (MEP)
monitoring. MEP loss indicated a severe unilateral
damage to the corticospinal system. This was
addressed by rapid decompressive resection of the
cerebellar tonsils until CSF drainage and gained
space by resection provided su cient decompres-
sion. A hemiparesis was seen postoperatively,
which fortunately, and in accordance with the
neurophysiological profile, was only transient.31
The routine use of intraoperative monitoring
for avoidance of neurological complications is
debated32 but not generally accepted.
Surgical decompression for Chiari II malforma-
tion is less frequently indicated. If it is performed,
the anatomy of the venous sinuses in the posterior
fossa must be appreciated. As the posterior fossa is
small and the sinus rectus steep, the torcula may
be quite close to the foramen magnum, and partic-
ularly in younger children an occipital sinus may
Chiari Malformations
225

be present, both of which pose a risk for serious
hemorrhage if opened.
27.9 Postoperative Care
Patients must be monitoring in an ICU setting
overnight after surgery. Postoperative pain ma-
nagement must be aggressive using acetamino-
phen, NSAID, and opioids to largely suppress
immediate pain from the rather large incision,
which involves—painfully—the neck muscles. Res-
piratory and circulatory monitoring is essential,
even though in this day and age respiratory
depression may indeed be a rare occurrence.
An MRI scan is recommended on postoperative
day 1 to document adequate decompression, rule
out hematoma, and provide an early comparison
of a syrinx to postoperative syrinx size as well as a
baseline for later assessment of syrinx evolution.
The patient must be mobilized out of bed on
postoperative day 1, and remains hospitalized for
a few days. External support with collars is
unnecessary and should not be considered; rather,
rapid norm alization of neck movement in spite of
initial pain should be encouraged. Skin sutures
must be removed after 2 weeks, to ensure healing
without CSF leakage. Patients should remain on
light activities after discharge. A postoperative sur-
gical visit should be scheduled after 4 to 6 weeks,
following which full activities can be resumed.
MRI follow-up is unnecessary if no syrinx was
present. In the presence of syrinx, a first follow-up
is recommended 3 to 6 months postoperative.
Later MRI follow-up depends on the evolution of a
syrinx.
27.10 Outcomes
Decompression of Chiari I malformation is usually
e ective in alleviating pain but not as much in
reversing already present neurologic dysfunction.6
Cerebellar symptoms apparently also respond
well to decompression.2 The results from decom-
pression in Chiari II patients appear to be less
favorable, a finding attributed to the underlying
developmental anomaly not treatable with
mechanical decompression alone. In Chiari II
patients, the underlying disability strongly defines
the clinical situation and this may be less due to
Chiari and more due to paraplegia. Syringomyelia
must be followed and the expectation is that a
syrinx will decrease in size or nearly obliterate
(Fig. 27.2).
27.11 Surgical Pearls
● Bony decompression aims at enlargement of the
foramen magnum.
● Lateral decompression at the foramen magnum
is essential.
● Removal of the posterior arch of the atlas must
be as wide laterally as the foramen magnum
decompression.
● Dural opening should be Y-shaped.
● The pia of the cerebellar tonsils is
microsurgically shrunk by carefully
applying bipolar coagulation, which is very
e ective in “pulling” the dislocated tissue
upward.
● Arachnoid strands become visible and may be
stretched upon shrinking of the tonsils and must
Fig. 27.2 MRI 10 years after surgery in
the same patient who has fully recov-
ered in 3 months after surgery with
normalization of the (a) posterior fossa
and no evidence for (b) syringomyelia.
Developmental and Congenital Cranial Disorders
226

be carefully divided to avoid ripping on the pia
of the brainstem or vessels that may be attached
in them.
● The dura is closed with an inverted triangular
piece of artificial dural graft which fits well into
the Y-shaped opening. Dural closure should be
with a running locked suture, as watertight as
possible.
● The muscular and fascial layers are tightly
sutured with individual size 1 resorbable
sutures. The fascial layer sutures are optimally
watertight when inverted and placed very close.
The skin should be closed with a watertight
running locked monofilic suture of size 3–0 or,
in smaller children, 4–0.
27.12 Common Clinical
Questions
1. Describe the primary pathology of Chiari I
malformation.
2. What are the most frequent signs and
symptoms of Chiari II malformation?
3. What would be a plausible indication for
surgery in a patient with an incidental finding
of Chiari I malformation?
4. Why is an artificial dural graft preferable to
an autograft such as fascia lata or
pericranium?
5. What is the treatment of syringomyelia
associated with Chiari malformation?
6. What is the co-prevalence of Chiari II
malformation and spina bifida?
27.13 Answers to Common
Clinical Questions
1. Displacement of the cerebellar tonsils below the
level of the foramen magnum and obliteration
of the cisterna magna.
2. Pain (Headache, Neck- and shoulder pain),
foramen syndrome, central cord syndrome,
cerebellar syndrome.
3. Presence of syringomyelia.
4. Because autografts tend to shrink with healing
and scar formation.
5. Craniovertebral decompression.
6. Chiari II only occurs in patients with spina
bifida.
References
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Hydrocephalie des Grosshirns. Dtsch Med Wochenschr.
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Developmental and Congenital Cranial Disorders
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28 Encephaloceles
Elizabeth J. Le, Rafael U. Cardenas, Mari L. Groves
28.1 Introduction
An encephalocele is a protrusion of cerebral tissue,
leptomeninges, and cerebrospinal fluid (CSF)
through calvarial and dural defects beyond the
confines of the skull, while a cephalocele refers to
the herniation of any combination of these compo-
nents.1 Encephaloceles may be rare neurodevelop-
mental lesions present at birth (primary) or
acquired due to traumatic, postsurgical, inflamma-
tory, or neoplastic causes (secondary).2
28.2 Classification
While several classification schemes have been
proposed in the past, current encephalocele classi-
fication is based on the anatomic location of the
skull defect (Fig. 28.1). These lesions are initially
divided into anterior and posterior groups. Within
the anterior division, encephaloceles may be sinci-
pital (extending between the frontal or facial
bones) or basal (protruding inferiorly through the
skull base), Posterior encephaloceles may be occi-
pital, occipitocervical, temporal, or parietal.3 Fur-
ther subclassification may be performed through
assessment of detailed computed tomography (CT)
or magnetic resonance imaging (MRI) for the
precise location of the lesion and its anatomic
contents.
28.3 Pathogenesis
Although the pathogenesis underlying the devel-
opment of encephaloceles is not fully understood,
these lesions are thought to develop from an error
in neural development occurring after primary
and secondary neurulation with incomplete ecto-
dermal dysjunction. During primary neurulation,
which occurs between the third and fourth gesta-
tional weeks, the future brain and majority of the
spinal cord form through a progression of embry-
onic folding and midline fusion. Abnormalities
arising during the initial closure of the neural tube,
at the rostral (cranial) neuropore, may result in
disorders such as anencephaly, in which the
involved neural tissue is exposed and disorgan-
ized. After primary neurulation, di erentiation of
the ectoderm (future epidermis) and neuroepithe-
lium (future brain and spinal cord) takes place.
Because encephaloceles typically contain well-
developed neural and mesenchymal tissues
encompassed by normal skin, their development
must ensue after primary neurulation.4 The char-
acteristic protrusion of neural tissue is thought to
arise during mesodermal di erentiation. Meso-
derm, which forms the meninges and skull,
normally migrates between the ectoderm and
neuroepithelial layers. However, scarring and
subsequent adhesion of these ectodermal layers
may prevent mesodermal intercalation. During the
Fig. 28.1 Classification of encephaloceles.
229

rapid growth of the telencephalon, even a small re-
gion of mesenchymal insu ciency or weakness
may allow for herniation of cerebral tissue extrac-
ranially5 (Fig. 28.2).
Both environmental and genetic factors may
promote the development of primary encephalo-
celes. For instance, the development of the poste-
rior variety has been associated with low maternal
fibrate levels, vitamin A usage, and exposure to
sodium arsenate, while the risk of developing ante-
rior encephaloceles has been correlated with
exposure to fungal molds and pesticides.6,7 Other
external causes of encephaloceles, such as warfarin
exposure and amniotic band syndrome, may
present with other associated findings.
28.3.1 Warfarin Syndrome
Low birth weight, mental retardation, hydroce-
phaly, seizures, nasal hypoplasia, bone stippling,
limb shortening, and optic atrophy.
28.3.2 Amniotic Band Syndrome
Tissue bands, ring constrictions and amputations
of digits or limbs, distal syndactyly, microcephaly,
irregular or asymmetric encephaloceles, micro-
phthalmia, bizarre orofacial clefts.
Though the vast majority of congenital encepha-
loceles are sporadic, there are rare cases of lesions
with genetic etiologies. While the molecular patho-
genesis underlying encephaloceles development
remains largely unknown, encephaloceles may be
found as a component of certain rare autosomal
recessive syndromes (Table 28.1).8,9,10,11,12,13
28.4 Epidemiology
The overall incidence of encephalocele is unknown
as the majority of congenital encephaloceles lead
to spontaneous abortion. Furthermore, epidemio-
logic data collection is di cult in developing
nations, where a significant number of these
lesions are found. Similarly, the true incidence of
secondary encephaloceles is also unknown. For
primary encephaloceles, the frequency varies
according to type and geographic location. The
overall incidence is reported as 0.8 to 3.0 per
10,000 live births, which accounts for approxi-
mately 10 to 20% of all cases of craniospinal dysra-
phism. Occipital encephaloceles account for 85% of
all encephaloceles and occur at a rate of 0.8 to 4.0
per 10,000 live births in North America, Europe,
and northern Asia, while sincipital encephaloceles
are significantly less frequent in these geographic
locations. Conversely, sincipital encephaloceles are
the most common type in Southeast Asia, areas of
Russia, and central Africa, where they may be
found in 1 in 5,000 live births, while occipital
encephaloceles occur at a lower rate. In most series
Fig. 28.2 Cross section of a chick embryo demonstrating features of the three embryonic germ layers. (Reproduced
with permission from Albright AL, Pollack IF, Adelson PD. Principles and Practice of Pediatric Neurosurgery. 3rd ed. New
York, NY: Thieme; 2015, Fig. 2.3.B.)
Developmental and Congenital Cranial Disorders
230

of congenital encephaloceles, the basal variety is
very rare in Western countries and represents only
5% of all cases.14,15,16
28.5 Clinical Findings and
Diagnosis
Encephaloceles may be diagnosed during the pre-
natal period through routine fetal ultrasound or
MRI, which may also provide detailed character-
ization regarding the location and type of lesion.
Amniocentesis may reveal normal to elevated
α-fetoprotein and acetylcholinesterase levels
depending on epithelialization of the encephalocele.
This inform ation m ay aid in prenatal counseling
regarding prognosis, as well as planning of deliv-
ery, postnatal surgery, and m anagem ent. A vagi-
nal delivery m ay be possible with relatively sm all
lesions, but larger encephaloceles m ay necessi-
tate a C-section.17,18,19
Although encephaloceles are usually obvious at
birth, subtle herniations may require a high level of
suspicion for detection, particularly in the setting of
other congenital abnormalities. MRI is utilized to
identify such occult lesions. During the postnatal
period, MRI is also used to classify encephaloceles,
demonstrate the extent of neural herniation, predict
the amount of functional cerebral tissue within the
sac, evaluate for the presence and degree of hydro-
Table 28.1 Congenital syndromes associated with encephaloceles
Syndrome

Description

Features
Walker–Warburg syndrome

The most severe congenital muscular
dystrophy, which affects development of
muscles, brain, and eyes
Caused by mutations of one of several
genes that produce proteins that
glycosylate α-dystroglycan
Hypotonia, muscle weakness/atrophy, lis-
sencephaly, hydrocephalus, cerebellar and
brainstem abnormalities, microphthalmia,
buphthalmos, corneal opacities, cataracts,
optic nerve abnormalities, retinal dysplasia,
occipital encephaloceles
Meckel’s syndrome

Characterized by polycystic kidneys,
encephaloceles, and polydactyly, as well
as a variety of neural tube, facial, cardiac,
bone, and genitourinary system
abnormalities
Caused by mutations in at least one of
eight genes that produce proteins in-
volved in cilia structure and function
Polycystic kidneys, polydactyly, occipital
encephaloceles, hepatic fibrosis, holopro-
sencephaly, microphthalmia, retinal dys-
plasia, orofacial clefts, ambiguous external
genitalia, other neural tube defects,
cardiac anomalies
Knobloch’s syndrome

Characterized by severe vision problems
and a skull defect
Caused by mutations in the COL18A1
gene that produces proteins that form
collagen XVIII
High myopia, vitreoretinal degeneration,
retinal detachment, macular degeneration,
normal intelligence, occipital encephalo-
celes
Roberts’ syndrome

Characterized by limb and facial abnor-
malities as well as intellectual impairment
Caused by mutations in the ESCO2 gene,
which makes a protein involved in
chromatid adhesion during cell division
Hypomelia, phocomelia, abnormal/missing
digits, joint contractures, orofacial clefts,
micrognathia, ear abnormalities, hyperte-
lorism, down-slanting palpebral fissures,
beaked nose, microcephaly, frontal
encephaloceles, heart, kidney, genital
abnormalities
Von Voss–Cherstvoy
syndrome
May represent a group of syndromes
with radial and hematologic
abnormalities
Unknown pathogenesis
Phocomelia of upper limbs, variable brain
abnormalities, urogenital anomalies,
thrombocytopenia, occipital
encephaloceles
Frontonasal dysplasia

Abnormal development of head and face
prenatally
Mutations in the ALX1 or ALX3 genes
(autosomal dominant inheritance with
ALX4 mutation) which make homeobox
proteins
Ocular hypertelorism, broad nose, no nasal
tip, orofacial clefts, frontal encephaloceles,
widow’s peak hairline, corpus callosal
abnormalities, intellectual disability
Encephaloceles
231

cephalus, and determine the presence of other
abnormalities of the craniocervical axis. Magnetic
resonance angiography/venography (MRA/MRV)
may be performed to assess for the presence of neu-
rovascular structures within the herniation sac and
characterize the relationship of the encephaloceles
to the surrounding vasculature. Further information
may be obtained from volumetric (three-dimen-
sional) CT imaging, which can aid in craniofacial
reconstruction planning.20,21
28.6 Surgical Management
While encephaloceles vary widely in location and
outcomes, the basic principles of management are
constant:
● Removal of the herniation sac.
● Preservation of functional neurovascular
elements.
● Prevention of CSF leakage through careful
closure of meninges and nondysplastic skin.
● Correction of cosmetic deformity.
Ongoing advances in neurosurgical technique, cra-
nial imaging, surgical equipment, and minimally
invasive approaches have made encephalocele
repair safer and more accessible.2,22,23
28.7 Posterior Encephaloceles
28.7.1 Clinical Findings
Posterior encephaloceles include lesions arising in
the occipital, occipitocervical, parietal, and temporal
regions. Herniation of cerebral tissue in each loca-
tion results in a variety of clinical findings.
Occipital Encephaloceles
Occipital encephaloceles typically occur in the
midline within the area between the lambda and
foramen magnum and may be supratorcular or
infratorcular, relative to their relationship with the
confluence of the sinuses. These lesions are nearly
always fully covered with skin and vary in appear-
ance, size, and content, ranging from small out-
pouchings containing only CSF and nonfunctional
gliotic tissue to large herniations sacs that may
include portions of functional cortex, brainstem,
and cerebellum involving the entire occiput. Fur-
thermore, the remaining intracranial contents tend
to move posterocaudally, resulting in the frontal
lobes being partially displaced into the middle fossa
and the posterior temporal lobes shifted into the
posterior fossa. Herniation of cerebral contents pos-
teriorly also results in displacement of the torcula,
transverse sinuses, and tentorium as well as brain-
stem distortion and kinking (Fig. 28.3).
Clinical presentation varies depending on the size
and contents of the encephalocele. Normal respira-
tions and neurologic function may be observed in
patients with only a small amount of cerebral her-
niation, while cranial nerve deficits, poor sucking
and feeding, spasticity, blindness, and developmen-
tal delay may be associated with larger masses.
In 15 to 20% of patients with occipital encepha-
loceles, other central nervous system anomalies or
neural tube defects may be found, such as cortical
Fig. 28.3 (a) T1 contrast-enhanced sagittal MRI demonstrates large occipital encephalocele with prominent vessels
within the defect. (b) T2 FLAIR (fluid-attenuated inversion recovery) axial MRI shows the extent of brain tissue contained
within the herniated sac. (c) T2 HASTE (half-Fourier acquisition single-shot turbo spin echo) axial MRI shows adequate
resection of the defect and reconstruction.
Developmental and Congenital Cranial Disorders
232

dysplasia, thalamic fusion, callosal agenesis or dys-
plasia, dysgenesis of the cecum and vermis, poste-
rior fossa cysts, an absent, rudimentary or inverted
cerebellum (ventral displacement of the cerebellar
hemispheres around the anterolateral aspect of the
brainstem), a small posterior fossa, and hydromye-
lia. In addition, hydrocephalus is present in 16 to
65% of cases. Hydrocephalus is important to identify
as it significantly a ects prognosis and outcome for
these patients (Fig. 28.4). Occipital encephaloceles
are also associated with cranial abnormalities such
as microcephaly, microphthalmia, facial clefts, skull
base deformity, and sloping forehead due to caudal
displacement of the frontal, temporal, and occipital
lobes. Other systemic anomalies in the cardiac,
renal, limb, and genital areas also frequently accom-
pany occipital encephaloceles and indicate a global
dysfunction of development.
Occipitocervical Encephaloceles
Occipitocervical encephaloceles include both a
cranial and cervical spinal defect. Again, clinical
presentation varies depending on the size and con-
tents of the encephalocele. However, hydrocepha-
lus is often a significant component of the clinical
presentation, with focal neurologic findings being
a less prominent feature. Associated congenital
anomalies may be found in 50% of children, similar
to those found with occipital encephaloceles.24
Parietal Encephaloceles
Parietal encephaloceles extend through defects
between the lambda and bregma. These lesions
also vary in configuration, from large lesions to
small subscalp lesions consisting only of dura,
fibrous tissue, and dysplastic brain tissue (atretic
parietal cephaloceles), which are thought to be an
involuted true encephaloceles.25 These lesions are
often accompanied by a variety of abnormalities
including Chiari II malformations, diencephalic
cysts, vermis agenesis, midline porencephaly, agen-
esis of the corpus callosum, holoprosencephaly,
communication with the lateral ventricles, and
Dandy–Walker cysts. In comparison to patients with
occipital lesions, parietal encephaloceles are associ-
ated with a highly unfavorable prognosis. The poor
functional outcomes are mainly due to the associ-
ated cerebral malformations, which are often more
frequent and severe than those found with the more
common types of encephaloceles.
Temporal Encephaloceles
Temporal encephaloceles arise at the pterion or
asterion and are often apparent during early
infancy, though some lesions may be an occult
cause of temporal lobe seizures.26 The clinical pre-
sentation may vary based on the particular loca-
tion of the herniation.
● Anterior temporal defects occur within the
sphenoid wing, resulting in herniation of brain
tissue into the posterior orbital area, causing
unilateral pulsating exophthalmos.
● Anterior medial defects occur in the anterior wall
of middle fossa and sphenoid sinus, often found
incidentally or due to CSF rhinorrhea
(Fig. 28.5).
● Posterior temporal defects project through the
tegmen tympani and extend into the tympanic
antrum or epitympanic recess. These lesions
Fig. 28.4 (a) Preoperative lateral view of the defect. (b) Axial non-contrast-enhanced CT shows large occipital
meningoencephalocele. Note the presence of significant ventricular dilatation (star). (c) 3D CT reconstruction
demonstrates large posterior calvarial bone defect. (d) Axial non-contrast-enhanced CTshows adequate reconstruction
of the defect with decrease in ventricular size after shunt insertion (shunt catheter not shown).
Encephaloceles
233

present with rhinorrhea, otorrhea, or CSF within
the middle ear, resulting in decreased hearing or
meningitis.
● Anterior-inferior temporal defects herniate
through the anterior floor of the infratemporal
fossa and most commonly present with simple
or complex partial seizures.
28.7.2 Surgical Management
For any encephalocele, the timing of surgery
should be based on the integrity of the skin
overlying the lesion, presence of other systemic
anomalies, and overall prognosis. When the skin
overlying the lesion is intact, surgery may be per-
formed electively. In the meantime, a thorough
evaluation by a pediatrician and geneticist should
be performed as well as complete examination of
the cranial vault and cervical spine with MRI and
possibly volumetric CT in order to aid in surgical
planning.
The outcomes of encephalocele repair are partic-
ularly reliant upon the proficiency of the surgical
team with treatment of such lesions as well as
pediatric patients in general. Given the rarity of
these anomalies, particularly in North America,
neurosurgeons or plastic surgeons m ay encoun-
ter only a few cases during their career. Most
would encourage such patients to be referred to
craniofacial centers with expertise in treating
encephaloceles. Sim ilarly, experienced pediatric
neuroanesthesiologists who can m eticulously
m aintain norm otherm ia and adequate blood vol-
um e in these patients are integral m em bers of
the surgical team in order to lim it the risk of
m orbidity and m ortality.
For occipital and occipitocervical lesions, the pa-
tient is positioned prone on a padded horseshoe
headrest overlying two well-padded chest rolls
with thorough cushioning of the face and pressure
points of the body, including the forehead, maxil-
lary eminences, chest, iliac crests, and knees.
Extreme care should be taken to prevent pressure
on the eyes. The neck may be flexed as needed
for adequate exposure, particularly in cases of
occipitocervical lesions. The encephalocele sac
should be secured to prevent inadvertent move-
ment that may cause torsion of the contents. The
occipital and upper cervical regions are then ster-
ilely prepared and draped. A horizontal or vertical
(for cervical or low-lying occipital encephaloceles)
elliptical skin incision extending circumferentially
around the lesion is made. Utilizing monopolar
cautery at a low setting, a dissection plane is cre-
ated between the skin and abnormal epithelium
to the pericranium. Violation of the galea should
be avoided in order to prevent significant blood
loss from the highly vascular scalp. This dissection
should extend from normal skin and skull to the
skull defect and neck of the herniation sac. With
cervical lesions, the normal cervical spine levels
caudal to the defect should be exposed with a
limited laminectomy. Subsequently, the plane
between the dura and the bone defect should be
carefully delineated. At this time, decompression
of the sac may be accomplished by CSF drainage
and the contents of the herniation sac may be
explored. Both gliotic tissue and abnormal neural
elements should be amputated, though any
normal neurovascular structures should be metic-
ulously preserved. A specimen may be sent for
culture. If possible, the dura may be closed pri-
marily, or with a dural graft (pericranium or colla-
gen-based dural substitutes) in order to achieve a
watertight closure. Frequently, the skull defect is
small enough that no graft is necessary. In some
larger defects, closure may be performed in a
delayed fashion once calvarial development is suf-
ficient to perform a split-thickness graft. If the
defect is large and early repair is necessary, an
autologous graft may be harvested from a rib or
Fig. 28.5 (a) Preoperative T2 coronal
MRI demonstrating a focal bony defect
in the greater wing of the sphenoid
with protrusion of temporal cortex and
CSF. (b) Bony defect is again demon-
strated in a coronal non-contrast-en-
hanced CT.
Developmental and Congenital Cranial Disorders
234

normal calvarial region. Other materials, such as
methyl methacrylate, hydroxyapatite bone cement,
and demineralized bone matrix may also be
utilized.27,28,29 In patients with large amounts of
herniated functional neural tissue and vascular
structures, “expansion cranioplasties” have been
described to aid in preservation of cerebral mate-
rial. In young infants capable of regenerating new
calvarial bone at the donor site, outward-expand-
ing barrel stave osteotomies are performed and
the skin opening is extended to adjacent parietal
regions with subsequent harvesting of full-
thickness craniotomy fitting the shape of the skull
defect. The donor site contains osteogenic dura
that will ossify and create new bone within 2 to
6 months.30 In addition, a variety of strategies
have been described to expand the intracranial
cavity in order to accommodate the herniated
neural elements. One method involves the use of
tantalum mesh to expand the cranium and incor-
porate the herniated brain tissue into the cranial
cavity. Daily digital compression of the tantalum
mesh is then used to slowly invaginate the resid-
ual encephalocele into the compliant cranial cav-
ity, obliterating it over a course of 3 to 4
months.31 A similar approach is the ventricular
volume reduction technique, which involves first
closing the encephalocele with a dural patch graft,
which then allows the intraventricular pulse pres-
sure to produce a hydrocephalic state. The herni-
ated neural elements are then transposed into the
enlarged intracranial cavity during ventriculoperi-
toneal shunting.32 After repair of the calvarial
defect or closure of dura, if cranioplasty is
deferred, redundant skin is resected and the skin
edges are approximated in order to achieve a
tension-free, cosmetic closure.
Parietal encephaloceles may be repaired simi-
larly to those of the occipital region. For temporal
encephaloceles, the location and size of the defect
dictates the approach. For encephaloceles of the
middle fossa, both the transmastoid approach and
middle cranial fossa approach, as well as a combi-
nation of both, have been used for repair. Larger
lesions may be approached more e ectively
through the middle fossa, while those impinging
on the ossicular chain may be better suited from a
combined procedure.33 Anterior temporal lesions
may be repaired through a standard pterional cra-
niotomy, while posterior encephaloceles may be
addressed with a subtemporal craniotomy.3 The
same principles regarding surgical management of
the herniation sac and closure apply regardless of
the approach.
Postoperatively, it is of utmost importance to
monitor for hydrocephalus in order to avoid CSF
leakage, which tends to occur more frequently
with posterior encephaloceles. The wound should
undergo frequent examination for evidence of leak-
age of CSF or the development of pseudomeningo-
cele. Head circumference should be measured daily,
while ventricular size should be monitored with
serial ultrasounds. A ventriculoperitoneal shunt
should be inserted if hydrocephalus becomes clini-
cally significant in order to prevent CSF leakage and
wound compromise.
28.7.3 Outcome
For all children with encephaloceles, approxi-
mately 40% can be expected to have a normal neu-
rologic and functional outcome, while 60% can be
expected to be significantly mentally and physi-
cally impaired. Historically, children with posterior
encephaloceles were thought to have worse func-
tional outcomes than those with anterior lesions,
with less than half of patients able to live inde-
pendently and function in society. Over time, inde-
pendent factors associated with neurologic status
have been determined, including the presence of
hydrocephalus, other brain abnormalities, seizure
disorders, and functional brain tissue within the
herniation sac.34 In fact, recent series of children
with treated encephaloceles demonstrated that the
location of the lesion was not a significant predictor
of outcome, while hydrocephalus and associated
intracranial anomalies were predictive of develop-
mental delay.35 Thus, children with occipital ence-
phaloceles may seem to exhibit worse physical, emo-
tional, cognitive, and overall health outcomes due to
the fact that hydrocephalus and seizure disorders
occur more frequently in children with occipital
encephaloceles compared to those with anterior
encephaloceles. The treatment of hydrocephalus and
seizure disorders can improve the long-term out-
come of these patients.36
28.8 Anterior Encephaloceles
Anterior encephaloceles may be either sincipital or
basal lesions.
28.8.1 Sincipital Encephaloceles
Sincipital encephaloceles are located within the region
of the foramen cecum, anterior to the cribriform
plate, and often present as a forehead or nasal/
Encephaloceles
235

nasional mass (Fig. 28.6). Further subclassification
occurs according to the location of the bone defect as
well the course of the encephalocele sac.
● Frontoethmoidal (interfrontal) encephaloceles
are relatively uncommon and produce a midline
forehead mass between the nasion and bregma.
They may be found in conjunction with large
lipomas of the subcutaneous tissues of the
forehead and corpus callosum.
● Nasofrontal encephaloceles extend through a
midline defect in the junction between the
frontal nasal bones. When small, they appear as
a small protuberance at the nasion, while
displacement of the nasal bones inferiorly and
the medial walls laterally occurs when they are
large. Furthermore, obstruction may result with
extension to the nasal passages.
● Nasoethmoidal encephaloceles occur at the level
of the foramen cecum with extension of the
herniation sac anteroinferiorly as it passes
between the nasal bones and nasal cartilage.
● Naso-orbital encephaloceles extend through the
frontal ethmoidal junction inferolaterally and
into the nasion and orbit at the level of the
middle third of the frontal process of the
maxilla. As a result, globe displacement,
telecanthus, and nasolacrimal duct dysfunction
causing epiphora and dacryocystitis may occur.
Severity of ocular deformity may range from
decreased global motility to anophthalmia.
Depending on the subtype, sincipital encephalo-
celes may present at birth as a visible mass causing
marked craniofacial abnormality or they may not
be detected until childhood or adulthood. While
nasoethmoidal lesions may be occult, all other sin-
cipital encephaloceles present at birth as a facial
swelling that enlarges with crying or Valsalva’s
maneuver. Furthermore, sincipital encephaloceles
are frequently accompanied by widening of the
nasion due to displacement of the medial orbital
walls (telecanthus), increased interpupillary distance
Fig. 28.6 (a) Preoperative image
demonstrating a frontoethmoidal
(sincipital) encephalocele. (b) Intra-
operative photo demonstrating repair
of the dural defect using a dural
substitute graft following excision of
the herniated glial tissue. (c) Sagittal
T2-weighted MRI and (d) Axial
T2-weighted MRI demonstrating the
frontoethmoidal encephalocele.
Developmental and Congenital Cranial Disorders
236

(hypertelorism), cleft lip and palate, craniosynostosis,
orbital dystopia, unilateral microphthalmos or
anophthalmos, and epiphora.
Sincipital encephaloceles should be di erentiated
from other growths that may also originate in the
naso-orbital or nasofrontal region, such as dermoid
cysts or teratomas with or without a dermal sinus
tract. Encephaloceles tend to be eccentric, pulsatile,
and enlarge with crying, while other masses typi-
cally occur in the midline, lack pulsation, and are
una ected by crying. Similarly, nasoethmoidal
encephaloceles, often detected in late childhood or
adulthood, may need to be distinguished from
nasal polyps. Encephaloceles occur more frequently
in children and tend to be located in the midline,
medial to the middle concha and attached firmly to
the medial surface of the septum. They may cause
nasal bridge widening and display a positive Fur-
stenberg’s sign, pulsation, and enlargement with
jugular venous compression. Nasal polyps, how-
ever, are rare in the pediatric patients and tend to
present as pedunculated masses arising from the
turbinates rather than the midline. They are not
associated with nasal bridge widening and have a
negative Furstenberg’s sign.3,37,38
28.8.2 Basal Encephaloceles
Basal encephaloceles present as mucosal-covered
masses protruding through the posterior aspect of
the anterior cranial fossa floor in the region of the
cribriform plate and planum sphenoidale. These
lesions may extend into the ethmoid sinus and
nasal cavity or through the sphenoethmoid junc-
tion or sphenoid sinus and into the epipharynx.
Because they are in close proximity to the supra-
sellar cisterns, they may contain important neural
structures such as the hypothalamus, pituitary
gland and stalk, optic chiasm, and vessels of the
anterior circle of Willis. Additionally, these lesions
may be occult and only detected during workup
for other neurologic deficits. Further subclassifica-
tion occurs based on the location of the herniated
encephalocele sac.
● Transethmoidal encephaloceles occur through a
defect within the cribriform plate that extends
through the ethmoid sinuses into the anterior
aspect of the nasal cavity.
● Transsphenoidal encephaloceles extend into the
epipharynx or sphenoid sinus.
● Sphenoethmoidal encephaloceles occur in the
posterior aspect of the junction between the
cribriform plate and sphenoid bone, extending
into the posterior nasal cavity.
● Sphenomaxillary encephaloceles extend into the
maxillary sinus.
● Spheno-orbital encephaloceles herniate into the
orbit via the superior orbital fissure and present
with proptosis and exophthalmos. Other
symptoms may include progressive visual loss,
microphthalmos, coloboma, hydrophthalmos,
anophthalmos, and microcornea. Other masses,
such as teratomas, may also occur in this area,
but encephaloceles can be distinguished by the
presence of nasal obstruction, CSF rhinorrhea,
and repeated bouts of meningitis.
While posterior encephaloceles are often associated
with multiple systemic anomalies, the associated
abnormalities of anterior encephaloceles tend to be
limited to the cranial region.2,39
28.8.3 Surgical Management
Similar to their posterior counterparts, anterior
encephaloceles are often covered by skin and, in
the absence of CSF leakage or airway obstruction,
these lesions may be treated electively. Again, a
thorough evaluation by a pediatrician and geneti-
cist should be performed as well as complete
examination of the cranial vault with MRI and
volumetric CT in order to aid in surgical planning.
Both the neurologic and cosmetic outcomes of
anterior encephalocele repair are particularly reli-
ant upon the proficiency of the surgical team with
treatment of such lesions as well as pediatric
patients in general. Treatment of anterior encepha-
loceles entails consideration of significant aes-
thetic and naso-orbital factors, such as correction
of telecanthus, maintenance of the horizontal ocu-
lar axis, correction of hypertelorism, preservation
of patent nasolacrimal ducts, and reconstruction
of nasal abnormalities, and many would advocate
that such patients be referred to craniofacial cen-
ters with expertise in treating complex craniofacial
abnormalities. Surgery often occurs through a col-
laboration of services. While the neurosurgical
team proceeds with encephalocele resection and
dural closure, the plastic surgery team takes
charge of cranial and craniofacial defect repair,
ocular and nasal reconstruction, and dermal
closure.
Anterior encephalocele repair should be per-
formed during early infancy in order to prevent
progressive craniofacial deformity due to an
enlarging, pulsatile herniation sac. Surgery may be
performed in a single operation or staged fashion.
Single operations tend to be the procedure of
Encephaloceles
237

choice. Similar to correction of single-suture syn-
ostosis in early infancy, early single operations to
repair anterior encephaloceles rely upon subse-
quent neurological and craniofacial development
to form the cranium for optimal aesthetic results.
Staged procedures occurring in later infancy and
childhood provide the benefit of avoiding signifi-
cant blood loss in an infant, interference with
anterior facial development, and telecanthus
recurrence after early reconstruction.
Both intracranial and extracranial approaches
have been described for anterior encephalocele
treatment. Intracranial approaches had been
favored as safer due to the ability to expose dural
defects and their contents as well as achieve a
watertight closure free of contamination within the
nasal cavity. The craniotomy utilized for an intra-
cranial approach can range from a large bifrontal
craniotomy to a small nasional craniotomy, with
the less invasive procedures being favored in appro-
priate cases. However, as surgical instruments and
techniques improve, minimally invasive endoscopic
approaches continue to increase in feasibility, safety,
and popularity. As with posterior encephaloceles,
the main goals of surgery are correction of the
deformity, prevention of CSF leakage, and preserva-
tion of functional neurovascular elements.
28.8.4 Sincipital and Basal
Encephaloceles—Intracranial
Approach
Prior to positioning, a lumbar drain may be placed
if a complex dural repair is anticipated, in the set-
ting of a large or relatively posterior defect, to aid
in brain relaxation, and to minimize retraction on
the developing brain. The patient is then posi-
tioned supine with the head on a padded horse-
shoe headrest. Thorough cushioning of the
pressure points of the body should be performed.
The encephalocele sac should be secured to pre-
vent inadvertent movement that may cause tor-
sion of the contents. The surgical field should then
be sterilely prepared and draped. Next, a bicoronal
incision is performed with meticulous hemostasis
with preservation of a large, vascularized pericra-
nial flap, which is reflected anteriorly. A bifrontal
craniotomy may then be performed just superior
to the floor of the anterior cranial fossa. For lesions
located within the ethmoid or planum sphenoi-
dale, such access will be su cient, though exten-
sion laterally through a pterional craniotomy or
temporally through a subtemporal craniotomy
may be required for lesions protruding into
the orbit or infratemporal fossa. Alternatively, a
smaller nasional craniotomy may be performed
below the bregma when appropriate for some sin-
cipital encephaloceles by removing a small rectan-
gular piece of bone extending from eyebrow level
to the tip of the nasal bone. The dura and base of
the encephalocele are subsequently mobilized
with inspection of its contents. If the contents do
not require preservation, ligation of gliotic and
nonfunctional tissue may be performed with care
taken to resect the herniated mass flush with the
floor of the anterior cranial fossa. With the
nasional craniotomy, transection of nonfunctional
tissue is performed parallel to the cribriform plate
with subsequent removal of herniated matter from
the orbits, maxillary, and nasal cavities. For basal
encephaloceles, volume reduction of the sac may
be more di cult as vital structures, such as the
hypothalamus, anterior cerebral arteries, optic
nerves, and optic chiasm, have a propensity to
herniate in this location. Every attempt should be
made to relocate vital structures into the cranial
cavity. When possible, the dura is repaired primar-
ily. The vascularized pericranial flap or collagen-
based dural substitutes may be used to achieve a
watertight closure when necessary. If needed, the
vascularized pericranial flap may also be used to
obliterate dead space and separate empty cavities
from the intracranial cavity. The skull base, nasal,
facial, and orbital deformities may be recon-
structed using autologous bone graft from the
infant’s calvaria or a split-thickness graft in an
older child.3,40
Following treatment of the encephalocele, facial
anomalies should be addressed. The nasolacrimal
ducts should be evaluated and preserved. If they
appear obstructed, cannulation or dacryocystorhi-
nostomy should be considered in order to prevent
the development of dacryocystitis. Orbital appear-
ance may be corrected through medial canthopexy
to align the horizontal ocular axis and orbital
translocation to reduce hypertelorism. Contouring
of the frontal and nasal bones may be performed
in order to create a normal nasofrontal angle. Fol-
lowing craniofacial repair, the skin edges of the
bicoronal incision are approximated in order to
achieve a tension-free, cosmetic closure.2,3
28.8.5 Endoscopic Repair—
Extracranial Approach
Historically, intracranial approaches have been
the preferred method for treating anterior
Developmental and Congenital Cranial Disorders
238

encephaloceles, particularly those of the basal
variety due to a tendency toward incomplete resec-
tion and postoperative CSF leaks with endoscopic
approaches. Though traditional open craniotomy
approaches allow for improved visualization and
require less technical expertise, disadvantages
include possible cosmetic deformity, disruption of
bony growth centers in children, and increased
morbidity. As surgical techniques and instruments
have evolved, safety, e cacy, and versatility of
endoscopic approaches have improved dramatically.
Recent series have demonstrated success rates of
88 to 100%, complication rates of 12 to 23%, and
failure rates of 15% for encephalocele repair using
endoscopic approaches, which is comparable to that
of transcranial approaches.41,42,43 It is now generally
accepted that minimally invasive approaches may
e ectively treat sincipital and basal encephaloceles
in the absence of significant craniofacial deformity
while avoiding a large coronal incision and craniot-
omy.44 Factors that may limit use of an endoscopic
approach include anatomic locations with limited
access (lateral frontal region), chronic sinusitis, prior
endoscopic sinus surgery, and unavailability of nasal
tissue for repair.41
In preparation for an endoscopic approach,
detailed preoperative imaging, frameless stereo-
taxis, and adequate endoscopic equipment (optics,
irrigation, instruments, and cautery) are essential.
The anterior skull base is typically accessed
through an endonasal approach through one or a
combination of four corridors, transnasal, trans-
sphenoidal, transethmoidal, and transmaxillary,
based on the location of the encephalocele. Once
accessed, the defect must be circumferentially
visualized with reduction of the herniation sac
until it is flush with the skull base. At the defect
site, the skull base should then be circumferen-
tially demucosalized. The mucosal graft should be
flush with the skull base and no overlap should
occur between the in situ skull base mucosa and
mucosal graft. Any overlap may result in mucocele
development. Grafting may be performed using
underlay, overlay, or combination of techniques
with a variety of potential graft materials including
septal mucoperiosteum, temporalis fascia, Dura-
Gen, cadaveric fascia, free mucosal graft, or vascu-
larized pedicled mucosal flap. Nasal packing is
then placed in both nares to minimize postoperati-
ve nasal bleeding and to bolster the closure. It is
typically removed within the first 24 hours post-
operatively. Postoperative antibiotic use is contro-
versial. Some advocate for antibiotics while nasal
packing is in place for 24 hours or during the first
72 hours after surgery.45
Preoperative lumbar
drain placement is also a nonuniform practice as
multiple series have shown a general decrease in
use over time with no significant impact on mor-
bidity or postoperative CSF leakage.41,45
Regardless of the approach, careful monitoring
and prevention of postoperative CSF leak should
be performed. The wound should undergo fre-
quent examination for evidence of leakage of CSF
or the development of pseudomeningocele. Head
circumference should be measured daily, while
ventricular size should be monitored with serial
ultrasounds. A ventriculoperitoneal shunt should
be inserted if hydrocephalus becomes clinically
significant in order to prevent CSF leakage and
wound compromise. Potential postoperative mor-
bidities include dacryocystitis, wound infection,
CSF leak, visual abnormalities, and anosmia.
28.8.6 Outcome
Historically, children with anterior encephaloceles
were thought to have better predicted outcomes
than children with posterior lesions. However,
this is more likely due to the fact that hydroce-
phalus and seizure disorders are less frequently
associated with sincipital and basal encephalo-
celes than occipital and parietal lesions. Further-
more, functional and neurologic outcomes for all
children with encephaloceles tend to worsen in
the presence of associated cranial, neuroanatomic,
and systemic abnormalities. Cognitive function
inversely correlates with the type and amount of
functional cerebral tissue within the herniation
sac. For patients with anteriorly located ence-
phaloceles, prognosis tends to be excellent, with
the exception of basal encephaloceles with her-
niation of vital structures. The m ajority of
patients with nasofrontal encephaloceles tend to
have norm al or nearly norm al intelligence and
ultim ately do well following repair of their con-
genital deform ity.34,35
28.9 Surgical Pearls
● Ensure adequate preoperative evaluation—all
medical abnormalities should be corrected prior
to surgical treatment in order to minimize
postoperative morbidity and mortality.
● Ensure adequate exposure—for anterior
encephaloceles, the craniotomy should be placed
low enough that the herniation sac can be
adequately accessed and completely resected.
Encephaloceles
239

● Ensure complete resection—inadequate
exposure and resection may lead to a persistent
facial mass in anterior encephalocele surgery.
● Ensure monitoring for hydrocephalus—failure to
identify hydrocephalus may lead to
postoperative CSF leak, wound dehiscence, and
infection.
28.10 Common Clinical
Questions
1. What is the prognosis of patients with
encephaloceles?
2. What are potential complications of anterior
encephalocele repair?
28.11 Answers to Common
Clinical Questions
1. For all children with encephaloceles,
approximately 40% can be expected to have a
normal neurologic and functional outcome,
while 60% can be expected to be significantly
mentally and physically impaired. Historically,
children with anterior encephaloceles were
thought to have better predicted outcomes than
children with posterior lesions. However, this is
more likely due to the fact that hydrocephalus
and seizure disorders are less frequently
associated with sincipital and basal
encephaloceles than occipital and parietal lesions.
Furthermore, functional and neurologic outcomes
for all children with encephaloceles tend to
worsen in the presence of associated cranial,
neuroanatomic, and systemic abnormalities.
Cognitive function inversely correlates with the
type and amount of functional cerebral tissue
within the herniation sac.
2. Potential complications include dacryocystitis,
wound infection, CSF leak, visual abnormalities,
and anosmia.
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Encephaloceles
241

29 Congenital Arachnoid Cysts
Gianpiero Tamburrini
29.1 Introduction
Congenital arachnoid cysts (ACs) are also called
leptomeningeal cysts. This term excludes secon-
dary “arachnoid” cysts (i.e., posttraumatic, postin-
fectious, etc.), lined with diseased or inflammatory
arachnoidal membranes, and glioependymal cysts,
lined with glial tissue and epithelial cells. True
arachnoid cysta tend to involve more frequently
the supratentorial compartment, sylvian fissure
cysts representing the most common location.1,2
Controversial issues do actually still exist concern-
ing both the indications to surgical treatment and
the type of surgery, the role of endoscopy having
reached an increasingly relevant role in this con-
text.3,4,5
29.2 Pathogenesis
True ACs are developmental lesions that arise from
the splitting or duplication of the arachnoid mem-
brane (thus they are in fact intra-arachnoid cysts).
The etiology of these lesions has long been the
subject of debate.
● The most accepted theory is that they develop
from a minor aberration in the development of
the arachnoid mater from around week 15 of
gestation onward, when the cerebrospinal fluid
(CSF) is generated to gradually replace the
extracellular ground substance between the
external and the internal arachnoid membrane
(endomeninx).1 The malformative hypothesis is
supported by the common location of ACs at the
level of normal arachnoid cisterns, their
occasional occurrence in siblings, the presence of
accompanying anomalies of the venous
architecture (i.e., the absence of the sylvian
vein), and the association with other congenital
anomalies (agenesis of the corpus callosum and
Marfan’s syndrome).
● Specific problems in the definition of the
pathogenesis concern intraventricular ACs. For
some authors, they represent a kind of “internal”
meningocele; for others, they derive from the
arachnoid layer and are transported along with
the vascular mesenchyme when they invaginate
through the choroidal fissure.1,6
29.3 Epidemiology
Congenital ACs have been reported to account for
roughly 1% of atraumatic intracranial mass lesions.
This relatively old figure is the result of a correla-
tion between data obtained from the clinical expe-
rience in the era before computed tomography
(CT)/magnetic resonance imaging (MRI) (0.7–2% of
space-occupying lesions) and those obtained from
autopsy observations (0.1–0.5% of incidental
autoptic findings)7; relatively recent MR studies in
healthy participants suggest that this rate is
higher, approximating 1.5 to 2.0%.8 Intracranial
ACs are nearly always sporadic and single. They
occur two or three times more often in males than
in females and three to four times more often on
the left side of the brain than on the right. The
bilateral occurrence of more or less symmetrical
cysts has been reported, although rarely, in normal
as well as in neurologically impaired children. In
the latter instance, especially in patients with
bitemporal cysts, the di erential diagnosis should
be made with lesions resulting from perinatal
hypoxia or metabolic diseases.
According to the information provided by large
mixed series (i.e., including both children and
adults), 6 to 90% of patients belong to the pediatric
age group; it is recognized that the largest propor-
tion of infantile cases occur during the first 2 years
of life.9
The most common location for ACs is within the
middle cranial fossa, 30 to 50% of lesions being
found there. Another 10% occur over the cerebral
convexity, 9 to 15% in the suprasellar region, 5 to
10% in the quadrigeminal plate cistern, 10% in the
cerebellopontine angle (CPA), and 10% in the mid-
line posterior fossa.1,2 The anatomical classification
and topographic distribution of the di erent types
of ACs are summarized in Table 29.1.
29.4 Sylvian Fissure Cysts
29.4.1 Epidemiology
Sylvian fissure cysts alone account for about half of
adult and one-third of pediatric cases. Their most
accepted classification is the one of Galassi and
242

colleagues who divided sylvian fissure cysts into
three types, depending on their size and apparent
communication (metrizamide CT study) with the
normal CSF spaces10 (Fig. 29.1).
29.4.2 Clinical Manifestations
Sylvian fissure cysts may manifest clinically at any
age, but they become symptomatic more fre-
quently in children and adolescents than in adults,
and in most series, infants and toddlers account
for about a quarter of the cases.
● The diagnosis is frequently incidental.
● In symptomatic patients, the symptoms are
often nonspecific, headache being the most
common complaint.
Controversies exist concerning the management of
asymptomatic children and children with aspecific
clinical symptoms. Preventive surgery has been
proposed with the objective of reducing the risk of
spontaneous/posttraumatic cyst rupture, with
consequent subdural hematomas, hygromas, and
intracystic bleedings. From a review of the most
recent literature, this risk is overall approximately
4.3% (relatively low), with the most frequent
occurrences being the one of subdural hematomas
(overall risk of 3.5%) and subdural hygromas (over-
all risk of 2.4%); intracystic bleedings have been
only rarely reported.11,12,13 The only risk factor
almost uniformly considered for cyst rupture is a
history of head injury, with 80 to 90% of the
reported cases being posttraumatic.11,12,13
● Cyst rupture might mean spontaneous
resolution of the cyst.14,15
● When symptomatic, rupture of the cyst in the
subdural space is usually related to mild and
gradually occurring clinical manifestations, so
leaving the time for an adequate management;
acute clinical symptoms are the object of
sporadic reports, mostly in adult patients.16,17
● Surgical treatment itself has a related risk of
postoperative subdural hygroma/hematoma,
which is similar to the one reported for
spontaneous/posttraumatic cases.18
● Surgery might not be able to prevent the rupture
of the cyst. From a recent endoscopic series of 40
patients, 10% had a subdural hematoma/
hygroma in the follow-up, in spite of the MR
evidence of a reduction of the cyst volume in
50% of them.19
Fig. 29.1 MR example images of arachnoid cysts of the sylvian fissure. (a) Type I: the cyst is confined to the temporal
pole. (b) Type II: the cyst extends to the middle third of the sylvian fissure. (c) Type III: the cyst extends to the whole
temporal fossa and presents suprasylvian extension.
Table 29.1 Anatomical classification and topographical
distribution of intracranial arachnoid cysts
Location

Percentage distribution
Supratentorial
● Sylvian fissure

30–50
● Sellar region

9–15
● Cerebral convexity

4–15
● Interhemispheric fissure 5–8
● Quadrigeminal plate

5–10
Infratentorial
● Median

9–17
● Cerebellar hemisphere

5–11
● Cerebellopontine angle
4–10
● Retroclival

0.5–3
Congenital Arachnoid Cysts
243

Among focal signs, mild proptosis and contrala-
teral motor weakness may be noted in advanced
cases.
● Seizures and signs of increased intracranial
pressure (IICP) represent the clinical onset in
about 20 to 35% of patients. When signs of IICP
appear acutely, they are usually the consequence
of an abrupt increase in the cyst volume,
because of subdural or intracystic bleeding.1,18
● Mental impairment is found in only 10% of the
cases; however, developmental delay and
behavioral abnormalities are common in
children with large lesions and are nearly
constant and severe in patients with bilateral
cysts.20,21,22,23,24
29.4.3 Radiological Findings
A localized bulging of the skull and/or asymmetri-
cal macrocrania are characteristic features in half
of the patients. CT in these cases reveals an out-
ward bulging and thinning of the temporal squama
and anterior displacement of the lesser and greater
wings of the sphenoid bone. Cysts appear as well-
defined lesions between the dura and the dis-
torted brain, with the same density of CSF and
without contrast enhancement. Cerebral ventricles
are usually of normal size or minimally dilated.6,10
MRI shows lesions to have hypointensity on T1-
weighted and hyperintensity on T2-weighted
images. Scanning of the vascular structures is use-
ful in order to define the arteries and veins in rela-
tion to the cyst wall. Cine-flow sequences have
been employed in the last 15 years as substitutes
for metrizamide CT in order to define the presence
or absence of communication between the cysts
and the subarachnoid spaces.25,26,27 This may be
particularly important in asymptomatic patients,
just as in patients with nonspecific clinical symp-
toms. In this context, further information that
might indicate the need for surgery may be pro-
vided by ICP monitoring.7,28,29,30 Perfusion MRI
sequences and SPECT (single-photon emission
computed tomography) studies have also been
proposed; the latter may help to evaluate brain
perfusion around the cyst walls.31,32,33,34,35
29.4.4 Surgical Management
There are essentially three surgical options, even
in combination:
● Cyst marsupialization through open craniotomy.
● Endoscopic cyst marsupialization.
● Cyst shunting.
Open cyst marsupialization is considered the pref-
erable surgical procedure. Successful open fenes-
tration rates vary from 75 to 100%; moreover, a
substantial reduction in the earlier morbidity rates
has been reported in recent series and surgical
mortality has been reduced to almost nil. Two
issues concerning open surgery should be pointed
out.
Total excision of the AC membranes is no longer
considered worthwhile; large windows in a bipo-
lar fashion are su cient to allow CSF pulsations
through the cyst cavity and reduce the risk of
harming the adjacent cortex. A more focal cyst
opening might also prevent CSF escape into the
subdural space and the development of postopera-
tive subdural hygromas.36
All vessels either traversing the cyst cavity or
lying in the cyst membrane represent the normal
vasculature and are therefore to be preserved.3
Pure endoscopic cyst marsupialization has been
proposed as an alternative to open fenestration in
recent years and has rapidly gained favor among
physicians.19,4 Endoscopy has also been used to
assist open surgery in order to reduce the exten-
sion of the surgical approach. Alternating results
of pure endoscopic techniques have been
reported, with success rates ranging between 45
and 100%.36
Cyst diversions are obviously safer, but are
accompanied by a high incidence of additional sur-
gical procedures (around 30%) and the stigma of
lifelong shunt dependency.31,3
29.5 Sellar Region Cysts
Sellar region cysts represent the second most com-
mon among supratentorial intracranial ACs.
A ected males slightly outnumber females, with a
male-to-female ratio of about 1.5:1. The cysts can
be subdivided in two groups:
● Suprasellar cysts that develop above the
diaphragma sellae.
● Intrasellar cysts that are found within the sellar
cavity.
The latter are far less common than the former and
are exceptional in children.
The term sellar region cysts includes neither the
“empty sella” syndrome, nor intrasellar and/or
suprasellar arachnoid diverticula. Metrizamide CT
or cine-MRI studies are helpful in the di erential
diagnosis, showing neither contrast entering nor
relevant CSF flow inside true cysts.5
Developmental and Congenital Cranial Disorders
244

It is largely accepted that sellar and suprasellar
ACs can be considered a consequence of a lobula-
tion of the prechiasmatic and interpeduncular
arachnoid complex, physiologically composed of
two distinct arachnoid sheets named as the
diencephalic membrane and the mesencephalic
membrane.
Intrasellar ACs are asymptomatic in about half
of the cases. Headache is the most frequent
complaint in symptomatic patients, and endocri-
nological disturbances are frequently associated.
Suprasellar cysts have been reported to be symp-
tomatic in more than 90% of cases. Most supra-
sellar cysts cause obstructive hydrocephalus since
a superior part of the cyst wall protrudes into
the third ventricle and thus obstructs the fora-
men or foramina of Monro. Obstructive hydroce-
phalus is the most common cause of the initial
signs and is reported in nearly 90% of the
patients. Ventriculomegaly may also be asymmet-
rical. Cases without any ventricular dilatation are
very rare. Visual field defect and/or decreased
visual acuity may occur due to compression of
the chiasm. Endocrine function may be a ected
due to deflection of the stalk, protrusion of the
cyst wall into the third ventricle, and very close
proximity of the cyst to the hypothalamic–pitui-
tary area. Growth hormone and corticotrophin
production are the most frequently compromised
hormonal activities Delayed menarche in women
may also be noted.5,37,38
Suprasellar ACs have been shown to compro-
mise neurocognitive function and psychological
profiles in the pediatric age group. A typical mani-
festation of a suprasellar cyst is the “bobble-
headed doll” syndrome, characterized by slow,
rhythmic movements of the head in an anteropos-
terior direction; it has been reported in approxi-
mately 10% of children with suprasellar cysts.5
During prenatal life, in the neonatal period, and
in infancy, echoencephalography is a useful diag-
nostic tool, allowing the evolution of this kind of
lesion to be followed during the first months of
life. An MRI examination should be performed
whenever technically feasible. There are three
characteristic diagnostic MRI features regarding
suprasellar cysts: (1) vertical deflection of the
optic chiasm/tracts, (2) upward displacement of
the anterior mesencephalon and mammillary
bodies, and (3) e acement of the ventral surface of
the upper brainstem (e.g., pons). MRI studies are
also important for the di erential diagnosis
between suprasellar ACs and other possible cystic
lesions of the sellar region (i.e., Rathke’s cleft cyst,
cystic craniopharyngiomas, epidermoid cysts, etc.)
(Fig. 29.2).5,37,38
The rapid advances in endoscopic technologies
have significantly changed the management of
sellar region cysts. The endoscopic transnasal
approach is ideally suited for pure intrasellar cysts
and has substituted the traditional microsurgical
approach to these lesions. Suprasellar cysts have
been managed by only opening the cyst roof
(endoscopic transventricular ventriculocystos-
tomy) compared with opening both the cyst roof
and the cyst floor (ventriculocystocisternostomy);
the latter technique is actually considered safe
and, if compared with ventriculocystostomy, is
associated with a lower recurrence rate (5–10% vs.
25–40%). In fact, chronic mesencephalic compres-
sion by the cyst may lead to secondary aqueductal
occlusion. In this scenario, apical membrane fenes-
tration alone, although allowing for adequate cyst
decompression, may not result in extraventricular
Fig. 29.2 Suprasellar arachnoid cyst.
(a) Axial T1 MR image showing the
extension of the cyst inside the third
ventricle and the posterior displace-
ment of the cerebral peduncles.
(b) Coronal T1 image showing the
extension of the cyst from the
interpeduncular cistern to the right
lateral ventricle.
Congenital Arachnoid Cysts
245

CSF flow. The basal membrane fenestration, on the
other hand, serves the purpose of allowing
trapped fluid to pass into the basal cisterns and
bypass the occluded aqueduct altogether. Shunting
procedures have been practically abandoned.
Although relatively safe, they are associated with a
surprisingly high percentage of reoperations.
Microsurgical excision, fenestration, or marsupiali-
zation has to be reserved for patients in whom the
endoscopic management has failed or for patients
with main extraventricular extension of the cyst
walls (i.e., suprasellar ACs involving the medial
aspect of the temporal lobe).5,38
It is important to remember that whatever the
surgical treatment, endocrinological problems, if
present, rarely resolve, with medical substitution
therapy being required in most cases; similarly
neurocognitive disturbances, when present, do not
tend to improve with surgery. Visual symptoms
and symptoms of intracranial hypertension, on the
other hand, improve remarkably after surgery.
Flow-sensitive MRI is needed to confirm a pulsa-
tion artifact in the follow-up period in order to
confirm the presence of stable communication
between the cyst and the CSF spaces.5
29.6 Cerebral Convexity Cysts
They are relatively uncommon (4–15% of all intra-
cranial ACs); females are more frequently a ected
than males. We distinguish between two main
varieties:
● Hemispherical cysts, huge fluid collections
extending over most or all of the surface of one
cerebral hemisphere.
● Focal cysts, small lesions generally involving the
cerebral convexity.
Hemispheric cysts have been considered to be
extreme extensions of sylvian fissure cysts, di ering
because of a compressed rather than an enlarged
sylvian fissure and the absence of temporal lobe
aplasia. They are most commonly discovered in
infants presenting with macrocrania, bulging ante-
rior fontanel, and cranial asymmetry. CT and MRI
allow the di erential diagnosis with chronic sub-
dural fluid collections (subdural hygroma and hem-
atoma) in most cases.39
Localized bulging of the skull usually suggests a
focal cyst. In children, typically, neurological signs
are lacking, whereas adults frequently exhibit focal
neurological deficits and/or seizure disorders. The
di erential diagnosis with low-grade neuroglial
tumors is usually made using MRI.1
Microsurgical cyst marsupialization is the treat-
ment of choice. It is not necessary to remove the
medial cystic wall, which is intimately connected
with the underlying cerebral cortex. Shunt implan-
tation is advised only in case of recurrences,
although it has also been proposed as a primary
procedure in infants with hemispheric cysts
because of their immature absorptive ability and
because of the related high risk of failure of open
surgical procedures. In such cases, programmable
valves are useful for better control of the intracys-
tic pressure and for favoring the development of
natural CSF pathways.1,31
29.7 Interhemispheric
Fissure Cysts
Interhemispheric fissure cysts are rare, accounting
for 5 to 8% of intracranial ACs in all age groups.
According to the classification by Mori,40 two main
types of interhemispheric cysts are recognized:
● Intra-axial interhemispheric cysts.
● Extra-axial interhemispheric cysts.
Intra-axial cysts are associated with more compli-
cated brain malformation, such as the dorsal cyst
of holoprosencephaly, diencephalic cyst with
upward extension of the third ventricle, and por-
encephalic cyst. In these cases, the cystic lesions
are in communication with the ventricular system.
Mori used the term dorsal cyst malformations to
indicate these lesions. On the contrary, extra-axial
cysts have no communication with the ventricles
or with the subarachnoid space and may exert mass
e ect on the surrounding brain.40
Distinction
between communicating and noncommunicating
cysts is usually easy on MRI. Noncommunicating
cysts show a typical wedge-shaped appearance in
coronal sections; di erently from communicating
cysts, the occipital horns of the lateral ventricles
can be easily identified, even though they are dis-
placed by the cystic lesion, and the basal ganglia are
normally separated.
Mori distinguished two types of extra-axial
cysts:
● Unilateral parasagittal cysts, with intact corpus
callosum.
● Midline cysts, associated with (partial or total)
agenesis of the corpus callosum and unilateral or
bilateral extension ( Fig. 29.3).
Usually extra-axial midline interhemispheric cysts
are associated with ventricular enlargement, often
Developmental and Congenital Cranial Disorders
246

asymmetrical: these cysts may distort the CSF
pathways, displacing downward one or both the
foramina of Monro, obstructing the aqueduct, or
impairing the resorption mechanism over the con-
vexity. Although interhemispheric cysts may be
sporadically discovered in adulthood and in eld-
erly patients, they are usually diagnosed in very
young children. Macrocrania is the presenting sign
in a large proportion of cases and symptoms of
intracranial hypertension develop in about two-
thirds of patients. Localized bulging of the skull is
the second most common finding. Neuroendo-
scopic management of interhemispheric cysts has
been proposed as first-line treatment in recent
years. Preoperative planning is essential through
careful evaluation of preoperative neuroradiologi-
cal investigations (in particular MRI with 3D TSE
techniques (DRIVE) sequences and CSF flow study)
to detect the thinner point of the cyst walls where
the stomy should be created with minimal brain
damage. Neuronavigation is extremely helpful in
placing a burr hole on the ideal trajectory and guid-
ing the endoscope through the target. Neuroendo-
scopic management is able to obtain a reduction of
the cyst volume and control of the hydrocephalus
in up to 85% of the cases.41,42
Postoperative imaging is essential to assess the
patency of the stomies and the patency of the sub-
arachnoid spaces in which the CSF is diverted after
the endoscopic procedure. They are also important
to detect possible complications related to the
rapid decrease of the cyst volume, such as sub-
dural hygromas. Long-term radiological follow-up
is mandatory to assess the decrease of the volume
of the cyst, which in most of the cases is very slow.
Craniotomy with excision of the cystic linings is
the treatm ent of choice. It allows the norm aliza-
tion of the ICP and brain expansion in the vast
m ajority of a ected patients. Because of the sig-
nificantly high rate of related complications,
shunting procedures should be considered only
in cases refractory to endoscopic or craniotom ic
approach.41
29.8 Quadrigeminal Plate
Region Cysts
Quadrigeminal plate cysts account for 5 to 10% of
intracranial ACs. Most are diagnosed in children,
with a slightly higher incidence in girls than in
boys.
Like interhemispheric cysts, although less fre-
quently, cysts originating in the quadrigeminal cis-
tern may be associated with other central nervous
system malformations such as holoprosencephaly,
Chiari type II malformation, and encephaloceles,
and tend to present in young children.41 Clinical
manifestations depend on the direction of expan-
sion of the cyst growth. The largest proportion of
these cysts develop upward into the posterior part
of the interhemispheric fissure or downward into
the cistern of the superior cerebellar vermis, with
the possibility, in selected cases, of both a supraten-
torial and infratentorial extension. Because of their
critical position along CSF pathways, these cases
are usually diagnosed in infancy because of the sec-
ondary obstructive hydrocephalus (Fig. 29.4).
Anomalies of pupillary reaction or eye move-
ments owing to compression of the quadrigeminal
Fig. 29.3 (a) Extra-axial interhemispheric arachnoid cyst with agenesis of the corpus callosum and (b, c) prevalent left
unilateral parafalcal extension.
Congenital Arachnoid Cysts
247

plate or stretching of the trochlear nerve may be
found; however, impairment of the upward conju-
gate gaze is relatively infrequent. When the direc-
tion of expansion is lateral in the cisterna ambiens,
hydrocephalus is usually absent and focal signs
can be found. Psychomotor retardation may be
related to delay in the treatment of intracranial
hypertension or to the rarely associated cerebral
malformations. Quadrigeminal cysts are not
homogeneous, but may have a di erent extension
toward surrounding regions. Sagittal median and
coronal MRI sequences clearly show the relation-
ship of the cysts with supratentorial and infraten-
torial ventricular and neural structures41,43
(Fig. 29.4).
As for sellar region cysts, modern neuroendo-
scopy has significantly changed the management
practice of this kind of lesion, once considered a
technical challenge. In the case of small lesions
(<1 cm) causing secondary triventricular hydroce-
phalus, third ventriculostomy should be considered
as the only surgical treatment needed. In larger
lesions, ventriculocystostomy should be performed,
possibly combined with third ventriculostomy in
patients with associated hydrocephalus. The
importance of third ventriculostomy associated
with the simple opening of the cyst wall has been
stressed by several authors.41,43 In fact, extrinsic
aqueductal stenosis arising from longstanding
compression by the cyst may persist despite cyst
opening. Approaching the ventricular system first
and hence the cyst (transventricular ventriculocys-
tostomy) appears to minimize the escape of CSF
into the subdural space, reducing the risk of post-
operative subdural collections. Although limited
series of patients appear in the literature, they uni-
vocally come to the conclusion that the endoscopic
management of quadrigeminal plate cysts is safe
and successful in almost all cases.41,43
29.9 Infratentorial Arachnoid
Cysts
Posterior fossa ACs are rather uncommon, repre-
senting approximately 15% of all intracranial cysts.
They should be distinguished from other cystic
malformations of the posterior fossa, namely the
Dandy–Walker malformation, the Dandy–Walker
variant, and the cystic evaginations of the tela cho-
roidea (i.e., the persistent Blake’s pouch). The main
di erentiating features of these di erent patholog-
ical conditions are summarized in Table 29.2.
Three varieties of posterior fossa ACs are recog-
nized:
● Midline cysts, which push the vermis anteriorly,
while separating the two cerebellar hemispheres
(Fig. 29.5).
● Hemispheric cysts, overlying and compressing
one cerebellar hemisphere.
● CPA cysts, displacing both the cerebellum and
the brain stem contralaterally44,45 (Fig. 29.6).
Clinical manifestations depend on the cyst location
and the age of the patient. In pediatric patients
with midline or hem ispheric cysts, macrocrania
Fig. 29.4 Quadrigeminal cistern
arachnoid cysts. (a, b) Interhemi-
spheric fissure extension of the cyst
and only partial obstruction of the
sylvian aqueduct not associated with
hydrocephalus. (c, d) Infratentorial
extension of the cysts and complete
obstruction of the aqueduct associ-
ated with secondary hydrocephalus.
Developmental and Congenital Cranial Disorders
248

Fig. 29.5 (a) Midline retrocerebellar
cyst, with anterior compression of the
vermis and (b) separation of the two
cerebellar hemispheres.
Table 29.2 Main di erentiating features of cystic malformations of the posterior cranial fossa and posterior fossa
arachnoid cysts
Dandy–Walker syndrome/
variant (DWS/DWV)
Blake’s pouch cyst

Posterior fossa arachnoid
cysts
Relationship with the fourth
ventricle
Cystic dilatation of the
fourth ventricle: borders of
the fourth ventricle not
recognizable in DWS; roof
and lateral borders present
in DWV
Fourth ventricle separated
in normal position or mod-
erately dislocated
Fourth ventricle separated,
compressed, and dislocated
Communication with the
subarachnoid spaces
Absent in DWS, present in
DWV
Present

Absent
Associated hydrocephalus

Present
(distinguishing feature)
Absent

Common
Associated cerebellar
anomalies
Partial or complete
agenesis of the vermis
Absent

Absent
Associated cerebral
anomalies
50–70% of the cases

Absent

Absent
Fig. 29.6 (a) Left cerebellopontine an-
gle arachnoid cyst, with clear com-
pression of the left cerebellar
hemisphere and (b) the presence of an
evagination of the arachnoid wall
(arrow) separating it from the cere-
bellopontine angle arachnoid cistern.
Congenital Arachnoid Cysts
249

and symptoms of intracranial hypertension are the
most frequent signs at presentation, in most
instances because of the common association with
hydrocephalus. Nystagmus and cerebellar signs
may be associated in patients with hemispheric
cysts. In adults, the clinical picture of a cerebellar
cyst is that of a slowly developing posterior fossa
mass, which usually has an intermittent course,
suggesting periodic volume fluctuations of the le-
sion. The secondary development of a Chiari I mal-
formation and syringomyelia has also been reported
as a picture disclosing the presence of the AC.44,45
Symptoms of CPA cysts include cochleovestibular
dysfunction, cerebellar signs, and, less frequently,
fifth and seventh cranial nerve deficits, as well as
pyramidal signs. Papilledema is often observed.45
MRI is the diagnostic investigation of choice for
posterior fossa cysts; flow-sensitive images have
increased its sensitivity allowing a more complete
preoperative diagnostic workup. CSF flow sequen-
ces are particularly important for patients who are
occasionally discovered to harbor a posterior fossa
AC or who present with aspecific clinical symptoms.
Communicating ACs have in fact been demon-
strated not to enlarge and hence to be considered
for a conservative approach and a follow-up that
might be limited in time.27
Direct microsurgical excision of the cyst walls is
currently considered the most appropriate type of
surgical management for patients with hemi-
spheric and CPA cysts. In patients with midline
cysts, relatively high rates of recurrence and per-
sistent postoperative hydrocephalus have been
reported, leading some authors to reconsider cyst
and/or ventricular shunting to be the preferable
surgical option/s. The main disadvantage of this
approach is the high rate of shunt malfunctions
that have been reported, with a frequency ranging
from 10 to 26% in this specific subset of patients.46
Neuroendoscopy has been recently introduced
into the management of posterior fossa cysts. Suc-
cessful endoscopic cyst marsupialization has been
reported in limited series of patients.46
29.10 Common Clinical
Questions
1. Does the risk of spontaneous/posttraumatic
rupture of sylvian AC justify a preventive
surgical treatment in asymptomatic children/
children with aspecific clinical symptoms?
2. What is the actually considered optimal surgical
management strategy for suprasellar ACs?
3. Is endoscopic cyst marsupialization of
quadrigeminal plate ACs considered su cient
for the control of both the volume of the cyst
and the associated hydrocephalus, when
present?
4. Which are the radiological anatomical features
which di erentiate a Dandy–Walker syndrome
from a posterior fossa retrocerebellar AC?
29.11 Answers to Common
Clinical Questions
1. No, the risk of spontaneous/posttraumatic
rupture of a sylvian AC is relatively low (3–5%);
it is controversial if surgery can prevent
following cyst rupture.
2. The optimal management strategy for
suprasellar ACs is endoscopic marsupialization
of the cyst to both the lateral ventricles and the
interpeduncular arachnoid cisterns.
3. No, it cannot help in controlling the
hydrocephalus in all cases; for this reason,
endoscopic third ventriculostomy should be
added to the endoscopic cyst marsupialization.
4. The main characteristic features of a
retrocerebellar AC which are not present in
Dandy–Walker syndrome are: (a) presence of
the fastigium; (b) compression of the vermis,
which is normally structured; (c) elevation of
the tentorium; (d) scalloping of the occipital
bone.
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third ventriculocystocisternostomy. Surg Innov. 2010; 17(3):
206–216
[39] Ulmer S, Engellandt K, Stiller U, Nabavi A, Jansen O, Mehdorn
MH. Chronic subdural hemorrhage into a giant arachnoidal
cyst (Galassi classification type III). J Comput Assist Tomogr.
2002; 26(4):647–653
[40] Mori K. Giant interhemispheric cysts associated with
agenesis of the corpus callosum. J Neurosurg. 1992; 76(2):
224–230
[41] Spennato P, Ruggiero C, Aliberti F, Buonocore MC, Trischitta
V, Cinalli G. Interhemispheric and quadrigeminal cysts.
World Neurosurg. 2013; 79(2) Suppl:20.e1–20.e7
[42] Cinalli G, Peretta P, Spennato P, et al. Neuroendoscopic
management of interhemispheric cysts in children. J
Neurosurg. 2006; 105(3) Suppl:194–202
Congenital Arachnoid Cysts
251

[43] Gangemi M, Maiuri F, Colella G, Magro F. Endoscopic
treatment of quadrigeminal cistern arachnoid cysts. Minim
Invasive Neurosurg. 2005; 48(5):289–292
[44] Arunkumar MJ, Korah I, Chandy MJ. Dynamic CSF flow study
in the pathophysiology of syringomyelia associated with
arachnoid cysts of the posterior fossa. Br J Neurosurg. 1998;
12(1):33–36
[45] Galarza M, López-Guerrero AL, Martínez-Lage JF. Posterior
fossa arachnoid cysts and cerebellar tonsillar descent: short
review. Neurosurg Rev. 2010; 33(3):305–314, discussion 314
[46] Cinalli G, Spennato P, Columbano L, et al. Neuroendoscopic
treatment of arachnoid cysts of the quadrigeminal cistern:
a series of 14 cases. J Neurosurg Pediatr. 2010; 6(5):
489–497
Developmental and Congenital Cranial Disorders
252

30 Neuroenteric Cysts
Peter A. Christiansen, John A. Jane, Jr
30.1 Introduction
Neurenteric cysts (NCs) are a rare spectrum of
cystic lesions derived from embryologically dis-
placed endodermal tissue that can present
throughout the entire neuraxis in any age group.1,2
With rare exceptions,3,4 NCs are benign and slow-
growing cysts suspected to arise from endodermal
nests of the foregut that fail to separate from the
notochord during excalation. NCs are most com-
monly found outside of the central nervous system
(CNS) in the posterior mediastinum and abdominal
viscera. Histologically, NCs resemble a simple cyst
lined with gastrointestinal (50%) and/or respiratory
(17%) type epithelium with ciliated and mucin-
secreting components. Distinct from other neuraxis
cysts, NCs contain a basement membrane and stain
with carcinoembryonic antigen. Wilkins and Odom
defined three groups of histological classification
(Table 30.1)5; however, there is no association
with clinical outcomes or management. Extremely
rare instances of adenocarcinoma have been
reported in the setting of recurrence.3
Corresponding to their embryologic origin from
primitive lung and foregut, NCs of the CNS usually
develop ventrally near the cervicothoracic junc-
tion and become less frequent further along the
neuraxis. Overall, spinal NCs are nearly 10 times
more common than intracranial and represent 0.7
to 1.3% of spinal axis mass lesions and 0.01 to
0.35% of cranial mass lesions.1,2,6,7
Clinical presentation is primarily progressive
local mass e ect that is often fluctuant (e.g.,
myelopathy/radiculopathy, limb weakness, cranial
nerve deficits, hydrocephalus) as well as focal
pain.6,8 Fluctuating symptoms are likely due to
spontaneous leakage and reaccumulation of cyst
contents. Accordingly, aseptic meningitis/mening-
mus and fevers are not unusual and spontaneous
rupture can even lead to hydrocephalus.8
Since clinical presentation is usually secondary
to mass e ect, spinal NCs present earlier with a
median age of diagnosis around 6 years, compared
to the intracranial median age of diagnosis of 34
years.2,6 Only around 20 intracranial NCs have
been reported in patients younger than 14 years.1
Gross total resection is recommended for sympto-
matic NCs.
30.1.1 Spinal
● Median age of diagnosis around 6 years.
● Ninety percent are intradural and
extramedullary.
● Less than 5% have any intramedullary
component.9
● Seventy percent found near the cervicothoracic
junction with the majority ventral to the
cord.10
● Mediastinal extension is possible.
● Bony vertebral anomalies characteristically
occur in most cases including hemivertebrae,
spina bifida, absence of vertebrae,
kyphoscoliosis, Klippel–Feil syndrome, split cord
malformation, and diastematomyelia.2,10
30.1.2 Cranial
● Median age of diagnosis in 30’s.
● Seventy to ninety percent located in the
posterior fossa in the prepontine,
cerebellomedullary, or cerebellopontine angle
cisterns.1,11
● Intraventricular, supratentorial, and
intraparenchymal locations are possible.
● Often misdiagnosed as arachnoid or epidermoid
cysts.
30.2 Radiographic Features
Due to variations in cyst contents, radiographic
characteristics are unable to make a definitive
Table 30.1 Wilkins and Odom’s histopathological
classification of neurenteric cysts
Type A
Single-layer pseudostratified cuboidal or col-
umnar epithelial cells mimicking the respira-
tory or gastrointestinal epithelium
Type B
Type A+ glandular invaginations; mucinous or
serous production; nerve ganglion, lymphoid,
skeletal muscle, smooth muscle, fat, cartilage,
bone elements
Type C Type A+ any associated glial elements or
ependymal cells
Source: Information originally described in Wilkins and
Odom.5
253

diagnosis of an NC. While there are exceptions to
every characteristic, the classic depiction is a well-
defined ovoid/lobulated homogenous nonenhanc-
ing cystic mass. A summary of the most frequent
findings is listed in the following.1,2,7,11,12,13
30.2.1 Computed Tomography
● Hypodense.
● No contrast enhancement.
● Adjacent bony abnormality (spine).
30.2.2 Magnetic Resonance
Imaging (MRI)
● T1: near-isointense to slightly hyperintense.
● T2: hyperintense.
● Fluid-attenuated inversion recovery (FLAIR):
Hyperintense without surrounding edema.
● Di usion-weighted imaging (DWI): Mild
restriction.
● MR spectroscopy: A large peak at 2.02 ppm
corresponding to N-acetyl aspartate-like
compound not seen in other cystic lesions.12,13
The radiological di erential includes arachnoid
cysts, epidermoid or dermoid cysts, choroidal cysts,
colloid cysts, Rathke’s cleft cyst, ependymal cysts,
cysts of parasitic or larval origin, and cystic tumors.
Arachnoid, choroidal, and ependymal cysts suppress
on FLAIR and have no DWI restriction. Rathke’s and
colloid cysts should be suspected based on location.
Dermoid and epidermoid have more intense DWI
restriction. Tumors and parasites tend to have con-
trast enhancement and surrounding edema.
30.3 Surgical Management and
Outcome
Gross total resection is the treatment of choice
for symptomatic NCs and can achieve a high
frequency of neurological improvement with
minimal morbidity. Neither radiation nor chemo-
therapy is recommended. Standard surgical
approaches are used to adequately expose the cyst
and its interface. E orts to contain cyst contents
will reduce postoperative chemical meningitis.8
Some advocate aspiration of cyst contents prior to
resection. Dissemination has been seen in a few
instances.14 Vertebral anomalies, extensive adhe-
sions, and/or intramedullary components usually
limit complete resection. Intramedullary cysts
frequently lack a clear dissection plane; therefore,
cyst marsupialization should be attempted. Partial
excision significantly increases the risk of recur-
rence and the need for further resection; however,
it has not been associated with worse long-term
outcomes.10 The longest reported follow-up dem-
onstrated a 37% recurrence rate,15 all among those
with partial resections. Recent studies have shown
recurrences can occur even with gross total resec-
tion. Recurrences have appeared between 4 months
and 14 years with a median of 36 months.10
Long follow-up periods with repeat imaging are
recommended.6
30.4 Common Clinical
Questions
1. Why are cranial NCs seen more frequently in
adults than pediatric patients?
2. What are the treatment options for NCs?
3. What radiographic characteristics would raise
suspicion for an NC?
30.5 Answers to Common
Clinical Questions
1. Presumably, NCs have been present since birth,
growing slowly. They usually only become
apparent when they begin to cause mass e ect.
Since most intracranial locations can
accommodate mass more readily than the
spinal canal, the presentation of intracranial
NCs is typically delayed until the adult years.
2. Complete surgical resection is widely believed
to be the ideal treatment as this relieves mass
e ect, minimizes the chance of recurrence, and
reduces the chance of dissemination.
Asymptomatic NCs have been followed with
serial imaging to closely observe their growth.
Not enough data are available to properly define
their natural history. Chemotherapy is not a
viable option since NCs are essentially
hamartomas and slow growing. Radiation
would have to target the thin cyst wall
with high risk of damaging nearby normal
tissue.
3. In pediatrics, NCs should always be in the
di erential with a cystic mass around the
cervicothoracic junction, particularly if there
are adjacent bony abnormalities. On MRI, a
nonenhancing cystic mass that does not
suppress on FLAIR and has slight DWI
restriction should bring NCs to mind.
Developmental and Congenital Cranial Disorders
254

References
[1] Gauden AJ, Khurana VG, Tsui AE, Kaye AH. Intracranial
neuroenteric cysts: a concise review including an illustrative
patient. J Clin Neurosci. 2012; 19(3):352–359
[2] Savage JJ, Casey JN, McNeill IT, Sherman JH. Neurenteric cysts
of the spine. J Craniovertebr Junction Spine. 2010; 1(1):58–63
[3] Dunham CP, Curry B, Hamilton M. Malignant transformation of
an intraaxial-supratentorial neurenteric cyst–case report and
review of the literature. Clin Neuropathol. 2009; 28(6):460–466
[4] Priamo FA, Jimenez ED, Benardete EA. Posterior fossa
neurenteric cysts can expand rapidly: case report. Skull Base
Rep. 2011; 1(2):115–124
[5] Wilkins RH, Odom GL. Tumors of the spine and spinal cord,
part 2. In: Vinken PJ, Bruyn GW, eds. Handbook of Clinical
Neurology. Amsterdam: North-Holland; 1976:55–102
[6] Al-Ahmed IH, Boughamoura M, Dirks P, Kulkarni AV, Rutka
JT, Drake JM. Neurosurgical management of neurenteric cysts
in children. J Neurosurg Pediatr. 2013; 11(5):511–517
[7] Preece MT, Osborn AG, Chin SS, Smirniotopoulos JG.
Intracranial neurenteric cysts: imaging and pathology
spectrum. AJNR Am J Neuroradiol. 2006; 27(6):1211–1216
[8] Choh NA, Wani M, Nazir P, et al. Intracranial neurenteric cyst:
a rare cause of chemical meningitis. Ann Indian Acad Neurol.
2013; 16(2):286–288
[9] Lippman CR, Arginteanu M, Purohit D, Naidich TP, Camins
MB. Intramedullary neurenteric cysts of the spine. Case
report and review of the literature. J Neurosurg. 2001; 94(2)
Suppl:305–309
[10] Garg N, Sampath S, Yasha TC, Chandramouli BA, Devi BI,
Kovoor JM. Is total excision of spinal neurenteric cysts
possible? Br J Neurosurg. 2008; 22(2):241–251
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Kapilamoorthy TR, Radhakrishnan VV. Neuroenteric cysts of
the brain-comprehensive magnetic resonance imaging.
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17(1):36–46
[13] Periakaruppan A, Kesavadas C, Radhakrishnan VV, Thomas B,
Rao RM. Unique MR spectroscopic finding in colloid-like cyst.
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Clin Radiol. 1985; 36(3):245–251
Neuroenteric Cysts
255

31 Intracranial Lipomas
Tina Lovén, Mark A. Mittler
31.1 Introduction
Intracranial lipomas are rare benign lesions, con-
sidered to be congenital malformations rather
than neoplasms or hamartomas. Lipomas make up
less than 0.1% of all intracranial lesions.1,2
There are multiple theories about the etiology
of intracranial lipomas. It is most commonly felt
that a persistent focus of the meninx primitiva dif-
ferentiates into adipose tissue and matures into
lipoma. The meninx primitiva surrounds the
developing brain. It represents the undi erenti-
ated mesenchyme and typically di erentiates to
form the leptomeninges. This theory would
explain the cisternal location lipomas, absence of
other mesodermal derivatives, and intralesional
location of blood vessels and nerves.3 The majority
of intracranial lipomas occur near the midline and
at embryological sites of neural tube flexion.4
More than half of identified intracranial lipomas
are associated with brain malformations such as
agenesis of the corpus callosum. This association
may result from the persistence of the meninx
primitiva at the location of lamina reuniens, block-
ing the formation of massa comissuralis. The e ect
on the development of the corpus callosum could
depend on the timing of this process.4
Intracranial vessels and nerves were noted to
course through the lipomas in 36% of the lesions.4
The relative frequencies of the locations of the lip-
omas correspond to the temporal sequence of dis-
solution of the meninx primitiva—explaining the
relatively high frequency of callosal lesions. Blood
vessels and cranial nerves generally pass through,
rather than be displaced by, the lipoma. Histology
demonstrates mature adipose tissue with incorpo-
rated nerve fascicles, arteries, and veins.5
Intracranial lipomas can grow slowly as part of
the general grow th of the body.3 While the natural
history of these lesions is not fully known, the
incidence of symptomatic compression from cere-
bellopontine angle (CPA) and dorsal brainstem lip-
omas suggests possibility of such grow th.3 These
lipomas have generally not been shown to grow
rapidly or undergo malignant change.6,7
31.2 Anatomy
Most intracranial lipomas are found in the midline
or at embryologic sites of neural tube flexion.4,5,8,9
The anatomic distribution of intracranial lipomas
was described by a retrospective review of
42 patients, identifying that 45% were interhemi-
spheric, 25% were in the quadrigeminal cistern,
14% in the suprasellar/interpeduncular cistern, 9%
laterally in the CPA, and only 5% more laterally in
the sylvian fissure.4 Other documented locations,
although less common, include hypothalamus,10
optic nerve,11
interpeduncular fossa,12
choroid
plexus,13 and cerebellar cortex.14
More than half of the patients with intracranial
lipomas had other brain anomalies.4 The most
common associated anomalies included: agenesis
or dysgenesis of the corpus callosum, cortical dys-
plasia, cerebral aneurysms, absence of septum
pellucidum, spina bifida, subcutaneous lipoma,
encephalocele, myelomeningocele, interhemispheric
cyst, Dandy–Walker malformation, and cranioverte-
bral anomalies.8,13,15
Certain congenital disorders are associated with
intracranial lipomas. Pai’s syndrome, for example,
is a genetic disorder characterized by median cleft
lip and palate, midline facial polyps, bifid nose,
and midline lipoma particularly in the corpus cal-
losum.16 Other disorders include frontonasal dys-
plasia, epidermal nevus syndrome, congenital
infiltration lipomatosis, and encephalocraniocuta-
neous lipomatosis.17,18 Anatomically, lipomas tend
to envelope adjacent nerves and vessels rather
than displace them. For example, in CPA lipomas,
the facial and vestibular nerves may course
through the lipoma without any clear plane of
dissection available to the neurosurgeon.11,18 Histo-
logically, a lipoma can contain elements of neuronal
tissue, calcifications, bone, cartilage, vessels, or
hematopoietic tissue but no ectodermal elements.8
Fat cells are mesenchymal type of mesoderm ori-
gin. They are widely distributed forming an inti-
mate admixture with other mesenchymal cells in
all body organs. Lipocytes are distinct from all epi-
thelial cells of the ectoderm and endoderm, to
which they become intimately related by apposition
of growing epithelial cells with budding reticuloen-
dothelial cells. Lipomas are trabeculated and fibro-
vascular, inseparable and indistinguishable from
the arachnoid matter. When they extend into the
underlying neural parenchyma, they do so along
the Virchow–Robin spaces, outside the pia matter.9
Lipomas are considered stable lesions; however,
myelolipomatous change has been documented in
256