Atlas-of-Neurosurgical-Techniques-Spine-and-Peripheral-Nerves

64
SpinalArteriovenous Malformations
487
.......
I
I
DII
.I. "'C':
II -
-,
.::'# \,~,
_ tit.'.
~ E
Figure64-6 (Continued)
(D) After opening
the dura and arachnoid the blue pial discoloration
overlying the cavernous angioma and intramedullary
hematomaare typical of these lesions. (E) A linear pial incision over the superficial
aspect of the angioma
and intramedullary
hematoma
permits ac-
cessto themfor excisionwith minimal manipulation ofthe cord. (From Oldfield11with permission.)
rI
/
Figure 64-7
Cavernous angioma of the
spinal cord. These mulberry-like lesions
are typically small (5-15 mm), have low
levels of blood flow. and are supplied by
delicate, thin-walled vessels.Removalof
cavernous angiomas issimilar to the exci-
sion of a benign intramedullary cord tu-
mor. After a linear. sagittal pial incision
over the most superficial portion of the
cavernousangioma. frequently indicated
by bluish-gray discoloration of the pia,
dissection of the distinct tissue plane be-
tween the surface of the lesion and the
gliotic tissue immediately surrounding it
is accomplished with the tips of bipolar
forceps and a microdissector. Because
residual portions of cavernous angiomas
left in situ during surgery may hemor-
rhage and cause recurrent myelopathy,
complete excision is mandatory and re-
quires careful and complete inspection of
the bed of the angioma for removal of
smallcompressedvesselsat the periphery
of the massin the spinal cord before clo-
sure. (From Oldfield"
with permission.)

I
488
Thoracic and Thoracolumbar Spine: Posterior Approach
over the most superficial aspect of the lesion require less
manipulation of the spinal cord for exposure, are associ-
ated with less risk of incurring additional
neurological
injury during surgery, and have a more favorable progno-
sis for improvement
after
removal, than
are ventral
lesions.. Summary
Dural AVFsare the most common type of spinal AVMand
the most amenable to treatment. Venous congestion, which
underlies cord injury in these lesions, is effectively treated
by interruption of the medullary vein between the dural
nidus and the coronal venous plexus. Embolization of an
untreated dural AVFin an acutely deteriorating patient may
References
1.
Rosenblum
B. Oldfield E, DoppmanJ,
DiChiro G. Spinal arteriovenous
malformations:
a comparison
of dural
arteriovenous
fistulas
and
intradural
AVMs in 81 patients.J
Neurosurg
1987;67:795-802
2.
Oldfield E. Spinal vascular
malformations.
In: Swash M. ed. Outcomes
in Neurological
and Neurosurgical
Disorders.
Oxford: Cambridge
Uni-
versity Press, 1998:134-155
3.
Hall W. Oldfield E. Doppman
JL. Recanalization
of spinal cord arteri-
ovenous
malformations
following
embolization.
J
Neurosurg
1989:70:714-720
4.
Niimi Y,Berenstein
A. Setton A. Neophytides
A. Embolization
of spinal
dural
arteriovenous
fistulae:
results
and
follow-up.
Neurosurgery
1997:40:675-682
5.
Criscuolo G. Oldfield EH, DoppmanJL.
Reversible
acute and subacute
myelopathy
in patients
with
dural
arteriovenous
fistulas:
Foix-
Alajouanine
syndrome
reconsidered.
J Neurosurg
1989:70:354-359
6.
Oldfield
E. DiChiro G. Quindlen
E. et al. Successful
treatment
of a
group of spinal cord arteriovenous
malformations
by interruption
of
dural fistula.J
Neurosurg
1983:59:1019-1030
stabilize the deficit and provide adequate time for definitive
surgical treatment.
Recent evidence suggests that most patients with ventral
thoracic
or lumbar intramedullary
AVMs can be stabilized
with serial embolization
with PYA.Certain AVMs(particu-
larly the tightly compacted
glomus-type
AVMsin a posterior
location and those in the cervical segments of the spinal
cord and certain peri medullary AVFs),are best treated surgi-
cally, either alone or after preoperative
embolization. Symp-
tom-producing
cavernous angiomas should be excised.
The outcome
after treatment
of dural AVFs,intradural
spinal AVMs,and cavernous angiomas is dependent not only
on type and location of the lesion but also on the preopera-
tive neurological
function. Patients who are ambulatory be-
fore treatment
are usually ambulatory
after treatment. Opti-
mal outcome requires early diagnosis and intervention.
7.
Mshar J. Doppman
J, Oldfield
E. Surgical
interruption
of intradural
draining
vein as curative
treatment
of spinal
dural arteriovenous
fistulas.J
Neurosurg
1995:82:196-200
8.
BiondiA.Merland J,Reizine D.Embolization with particlesin thoracic
intramedullary
arteriovenous
malformations:
long-term
angio-
graphic and clinical results. Radiology 1990; 177:651-658
9.
Djindjian
M, Djindjian
R. Rey A, Hurth
M. Houdart
R. Intradural ex-
tramedullary
spinal arteriovenous
malformations
fed by the anterior
spinal artery. Surg NeuroI1977:8:85-93
10.
Gueguen
B. Merland J. Riche M. Rey A. Vascular malformations ofthe
spinal cord: intrathecal
peri medullary
arteriovenous
fistulas fedby
medullary
arteries.
Neurology
1987;37:969-979
11.
Oldfield
E. Spinal
vascular
malformations.
In Wilkins, RH. and
Rengachary,
SS. ed. Neurological
Operative
Atlas. Vol 4. Chicago:
American Association
of Neurological
Surgeons;
1994:1-18

65
Intradural Extramedullary Tumor Resection
inthe Thoracic Spine
DonaldA. Smith and Thomas B. Freeman
.
Indications
.
Contraindications
.
Advantages
.
Disadvantages
.
Case Selection
and Surgical
Approach
Intraspinaltumors account for 15 to 20%of primary central
nervoussystem (CNS)neoplasms.l-3lntradural
tumors are
classically
subdivided
into
intramedullary
and
ex-
tramedullary types, each with
distinctive
pathology
and
prognosis. Extramedullary
tumors
make
up -70%
of in-
tradural neoplasms,
are almost
always
benign,
and lend
themselves to total
surgical
excision
in most
instances.
Meningiomas, schwannomas,
and neurofibromas
together
account
for over 90% of these lesions.
Symptomaticpresentation is nonspecific and may include
localpain,radiculopathy, or myelopathy. Meningiomas and
nervesheath tumors occur with almost equal frequency, al-
thoughmeningiomas exhibit a marked sex predilection, with
80%occurring in females.2 The majority of these originate in
the lateral or posterolateral
meninges
of the thoracic spine.
Nervesheath tumors occur both sporadically and as part of
theneurofibromatosis syndrome. Extramedullary spinal tu-
morsin the neurofibromatosis type 1 (NF1) population are
usuallyneurofibromas, whereas nerve sheath tumors pre-
sentingin NF2patients and in the general population are al-
mostexclusively schwannomas.4 They originate preferen-
tially within
the
ensheathing
elements
of the
posterior
(sensory) rootlets,
but with continued
growth
incorporate
theanterior rootlets also and may infiltrate along the axis of
the spinal root in the neural foramen and beyond, presenting
asa"dumbbelltumor," with both intra- and extradural com-
ponents. Nerve sheath
tumors afflict the sexes equally, and
they are distributed
relatively evenly throughout
the spine.2
. Indications
. Symptomaticity
. Significantcordcompromiseon neuroimagingstudies
. Tumorprogressionon serialimagingstudies
.
Objectives
. Surgical
Technique
Preparationand Positioning
Closure
.
Contraindications
. Medical infirmity precluding general anesthesia
.
Advantages
.
Direct,straightforward exposure
. Excellentvisualizationof
normal
and
pathological
anatomy
.
Good access for extended exposure to neural foramen
and paraspinal tissues
.
Affords easy dural repair and opportunity
for any re-
quired spinal stabilization/reconstruction
.
Disadvantages
. Visualization
of pathology
directly
anterior
to the cord
suboptimal
. Case Selection
and Surgical
Approach
Unless medical contraindications to surgery exist, patients
with symptomaticlesionsare generallyadvisedfor opera-
tion. Incidentally discovered tumors with significant defor-
mation of the spinal cord may benefit from surgery even
while asymptomaticifa lifeexpectancyof at least several
years is probable. Asymptomatic lesions are routinely de-
tected in the neurofibromatosis population, and these are
generally monitored clinically and radiographically until
symptoms intervene or critical progression is documented.
489

490
Thoracic and Thoracolumbar Spine: Posterior Approach
.
Objectives
Total excision of intradural extramedullary tumors is the
surgical goal and may necessitate sacrifice of an involved
nerve root. With the exception of the T1 root. such sacrifice
is without significant functional consequences in the tho-
racic spine. Excellent outcomes are customarily achieved in
the great majority of these lesions. Early detection of tu-
mors with modern neuroimaging techniques and the use of
steroids perioperatively have contributed significantly to
these excellent results. Surgery has also been considerably
facilitated through intraoperative adjuncts such as ultra-
sonic localization. electrophysiological monitoring. the op-
erating microscope. ultrasonic aspirators. and the surgical
laser. Agreater understanding of spinal biomechanics and
improved technology for spinal reconstruction are addi-
tional factors that have enabled more thorough resections
of certain complex lesions while averting complications re-
lated to spinal instability.
. SurgicalTechnique
Most intradural extramedullary tumors arise in the lateral
or posterolateral quadrants of the spinal canal and are read-
ily exposed using techniques of laminectomy familiar to all
neurosurgeons. Besides technical simplicity and excellent
visualization of both the normal and the pathological
anatomy. a direct posterior approach affords easy access en-
abling a watertight dural repair and any requisite spinal re-
construction or stabilization. More anteriorly situated tu-
mors and those with foraminal extension can be addressed
by combining laminectomy with medial or total facetec-
tomy. Larger tumors with significant extension into the
pleural cavity or mediastinum may require supplemental
posterolateral
(costotransversectomy)
or anterolateral
(transthoacic) exposures.
Preparation and Positioning
Patients with tumors impinging on the spinal cord are be-
gun on high doses ofcorticosteroids preoperatively. Surgery
is routinely performed under general anesthesia in the
prone position and prophylactic antibiotics are utilized.
Great care is taken to pad all contact points and to avoid ap-
plication of any pressure to the eyes. The central chest and
abdomen should hang free to enhance respiratory mechan-
ics and minimize pressure in the epidural venous plexus.
Operating on a radiolucent table enables the use of antero-
posterior (AP)fluroscopy to assist with intraoperative tumor
localization and placement of the surgical incision. Muscle
relaxation simplifies the soft tissue and bony exposure but is
avoided once intradural dissection commences so that spon-
taneous and evoked motor responses may be more readily
observed. When myelopathy is present or the cord is grossly
deformed. the functional integrity of the spinal conduction
pathways is monitored in real time with sensory and motor
evoked potentials. A nerve stimulator and the ability to
record nerve action potentials can be useful in guiding the
isolation of a tumor from an involvedT1root.
-
Laminectomy
As a rough guideline. the skin incision will need to extend
two spinal segments above and below the targeted spinal
level. Soft tissues are incised in the midline to the levelof
the deep fascia. and self-retaining retractors are placed.
Paraspinal muscles are reflected off the spinous processes
and laminae laterally to uncover the facet joints. Extending
the soft tissue dissection one level above and belowthetar-
get segment(s) provides an unencumbered exposure.Before
commencing the laminectomy it is mandatory to reconfirm
accurate localization of the surgical exposure radiographi-
calIy.
The laminectomy should uncap both the rostral andthe
caudal poles of the tumor. Ahemilaminectomy maysuffice
for small laterally situated lesions. but when in doubt.itis
always better to err on the side of a more generousexpo-
sure. The sublaminar insertion of any rongeurs intoaspinal
canal already narrowed by tumor can easilyimpaircord
function. This is easily avoided by using an en bloc
laminectomy
technique
using high-speed
drills under
loupe magnification and continuous irrigation. Troughsare
cut in the laminae lateralIy at the level ofjuncture withthe
facet joint (Fig. 65-1). It is easy to appreciate penetration
of the inner cortex of bone with the drill. at whichtime
strands of ligamentum flavum herniate upwardly intothe
Figure 65-1
Lateral troughs being cut on each side at the junctionof
the laminae
with the medial
facet.

65
IntraduralExtramedullaryTumorResection
491
bonydefect.Once the laminar troughs are complete. a
nerve hook can be used to elevate the ligamentum for
sharpcircumferentialdivisionaroundthe perimeterofthe
laminectomy.The laminae are then lifted off en bloc as a
Penfieldno.4 dissector is used to carefully tease away any
fineremainingepidural attachments from its undersurface
(Fig.65-2). Bleeding from within the epidural space em-
anatesfromthe lateralgutters and is readilytamponaded
withthin strips of thrombin-soaked
thrombostatic agent.
Bonebleeding is controlled with wax as required. The drill
canbe used to enlarge the laminectomy laterally or to add
amedialor total facetectomy should either of these mea-
suresbe required. It is very important to establish absolute
hemostasisat this point because any continued epidural
oozingwill detract significantly from the subsequent in-
traduralmicrodissection and may contribute to intradural
adhesionspostoperatively. The adequacy of the bony expo-
sureshould be verified by ultrasound. It is far more conve-
nient to correct any deficiencies in the exposure at this
pointthan after the durotomy has commenced.
Durotomy
Thedura is grasped with a fine hook or suture and tented
upwardprior to its incision in an effort to spare the under-
lyingarachnoid membrane and to avert spinal cord hernia-
Figure65-2
Laminectomy block with lateral drill troughs, being
lifted off dura.
tion. Asomewhat curved incision offset toward the side of
the tumor enhances the lateral exposure. The dural opening
should encompass the full rostral-caudal extent of the le-
sion (Fig. 65-3). Tack-up sutures are placed to avert the
dural edges, and cottonoid strips are directed superiorly and
inferiorly within the subdural compartment to retard reflux
of blood from the epidural space. If the tumor is partially
concealed beneath the overlying spinal cord, repeat ultra-
sound imaging will reorient the operator to the hidden
anatomy and reconfirm that the exposure is sufficient.
Tumor Resection
For purely dorsally situated lesions loupe magnification
may be entirely satisfactory. Nerve sheath tumors arise
within the arachnoid envelope whereas meningiomas are
extra-arachnoidal. In small meningiomas it maystillbe pos-
sible to appreciate and preserve this anatomical distinction.
Bythe time most of these tumors come to clinicalattention
this nuance is no longer apparent, and so microdissectionof
the arachnoid commences at an interface between the
spinal cord and tumor. Seldom is there difficulty in develop-
ing this plane. Dissection progresses circumferentially in an
effort to define the relationship between the tumor and the
exiting nerve roots. Small nerve sheath tumors often arise
in relation to dorsal sensory rootlets, and in these instances
Figure 65-3
Curved dural incision being opened sharply with a sub-
dural cottonoid
protector
at one end, sparing the arachnoid.

492
Thoracic and Thoracolumbar Spine: Posterior Approach
it may be possible to spare the ventral rootlets. However,as
the tumor enlarges, and especially in the case of neurofibro-
mas, the ventral rootlets and spinal root are engulfed,
frequently precluding their anatomical preservation. The
surgical objective is to remove the tumor while minimizing
all physical manipulations of the spinal cord. Forvery small
tumors this may be achievable with an en bloc removal
once the appropriate arachnoidal dissection planes have
been established. Largertumors are removed in a piecemeal
fashion, working alternately within the tumor to slacken it
through internal debulking, and then outside the tumor to
advance the plane of dissection (Fig. 65-4). Many of these
lesions have a relatively soft consistency, which lends itself
to internal debulking using a combination of simple suc-
tion, sharp dissection with microscissors, and low-power
bipolar technique. Tumor resection begins laterally to mini-
mize physical and thermal trauma to the spinal cord. More
resistant tumors can be cautiously debulked with an ultra-
sonic aspirator or a surgical laser. Some meningiomas can
be quite calcified and resistant to even these modalities. In
these instances, sharp dissection may be the only option,
and it may be safer to leave behind a thin rind of tumor at-
tached to the spinal cord in the interests of functional
preservation.
The surgical microscope is routinely utilized whenever
the dissection progresses anterior to the plane of the den-
tate ligament. Largerventrally situated tumors tend to dis-
place the cord dorsally and rotate it toward the opposite
side. Maintenance of these dislocations temporarily as de-
bulking proceeds can be advantageous to the ongoing de-
velopment of the plane of dissection between tumor and
Figure 65-4
Tumordissection inprogress,withinternalgutting and
developmentofa tumor-cord interface.
Figure 65-5
The spinal cord being rotated with traction sutures
placed in the dentate ligament.
cord. This is accomplished by placing fine 6-0 tractionsu-
tures into the laterally severed dentate ligament ordivided
posterior rootlets or through the arachnoid itself (Fig.
65-5). This maneuver helps hold the cord in its dorsallydis-
placed and rotated position, thereby facilitating visualiza-
tion of the tumor and its ventral dissection. In rare in-
stances the cord may be purposefully rotated to enhance
the exposureofa directlyanteriorlysituatedlesion,butthis
is performed with utmost caution and must be abandoned
at the earliest decrement in the sensory or motorevoked
potentials. Ventral visibility is also enhanced if a facetec-
tomy has been performed prior to durotomybecausethis
adds a few more degrees of obliquity to the viewingangle
attainable with the microscope.
Meningiomashave a point of dural attachment.Ideally
this should be excised to minimize the risk of tumor recur-
rence. In dorsally situated lesions this is an easilyattained
goal because subsequent watertight dural repairwitha
patch graft is readily performed. Excisionand repairofven-
tral dural attachments are more challenging. Fortunatelyit
is usually sufficient to resect only the inner leaf ofthe dura
at the point of tumor origin with extensive bipolaringofthe
remaining outer leaf (Fig. 65-6). In nerve sheath tumors
with dumbbell extensions, the intradural dissectioniscom-
pleted first so that there is no possibility of transmitted
traction injury to the cord during extradural dissection.The
durotomy is extended laterally out along the axis ofthe ex-
iting spinal root to expose any foraminal and proximalex-
traforaminal component.
Tumors with significant intrathoracic extension mayre-
quirethe additionofa costotransversectomyexposurewith
l

---
65
IntraduralExtramedullaryTumor Resection
493
Figure65-6
Completed resection with coagulation of the outer
duraleaf.
resectionof the adjacent transverse processes and proxi-
malribs. It is desirable to avoid entry into the pleural cav-
ity,but a simple rent in the parietal pleura without air leak
doesnot necessitate a chest tube. In the absence ofviola-
tionofthe visceral pleura, such tears are repaired primarily
withsuture if no bubbling is detected during positive pres-
sureventilation after the wound has been flooded with
saline.Ifchest tube drainage is required, the potential for
cerebrospinalfluid(CSF)fistulizationis reduced byan as-
siduousdural closure and isolation of any potential com-
munication between the intradural and intrapleural com-
partments with fat or muscle grafts and fibrin glue. Larger
tumors invading the mediastinum
and attached to the
greatvessels are best addressed through a staged transtho-
racicresection after the intraspinal component has been
dealtwith.
Closure
Priorto closingthe dura the wound isthoroughlyirrigated
andabsolute hemostasis is confirmed. Arachnoid trabeculae
aredisrupted and any residual blood is washed away in
hopes of preempting the postoperative
development of
arachnoidal adhesions and extra- or intramedullary cysts
consequent to impaired CSFflow. The dura is reapproxi-
matedin a watertight fashion with a running or running-
locksuture. If a primary repair is not achievable. a dural
patchgraft is sewn into place (Fig. 65-7). Care is taken to
excludearachnoid from the edges of the dural closure. An
estimate of the integrity of the closure is gained through
performance of a Valsalva's maneuver while watching for
egressof CSFfrom the dural repair. Watertight closure may
beelusive when dealing with ventral defects, and in these
Figure 65-7
The dura closed with a running stitch and patch graft.
instances. a stamp of autologous fat or muscle and a smear
of fibrin glue are frequently successful.
Any indicated spinal stabilization or reconstruction
is
performed at this stage. Fusion after unilateral facetectomy
in the thoracic region is not mandatory. Fusion is advisable
after bilateral facet disruption or in the presence of an un-
derlying kyphotic or scoliotic deformity. This is customarily
combined with spinal instrumentation
appropriate to the
level of the spine involved and the type of corrective forces
required. In the upper- and midthoracic spine this would
typically involve a hook-rod construct clawed above and
below the destabilized segment; in the lower thoracic spine
the pedicles may be of sufficient size to accommodate pedi-
cle screws. We eschew the use of deep wound drains in in-
tradural procedures because of the potential to promote CSF
fistulization.
Meticulous attention to the soft tissue closure also con-
tributes to the avoidance ofCSFleaks postoperatively.sDead
space is reduced through reapproximation of the paraspinal
muscles with large absorbable sutures. Deep fasciaisclosed
with closely spaced interrupted sutures. In the absence of
prior operation or irradiation this is seldom problematic,
but if a tensionless
closure cannot be achieved. the
suprafascial tissues are undermined and lateral relaxation
incisions are placed in the fascia. The adipose tissue is
closed in at least two further layers, also with interrupted
sutures. In a final effort to limit the potential for wound fis-
tulization.
the skin is reapproximated
with a running
monofilament suture. In upper thoracic procedures shoul-
der tapes are applied postoperatively to discourage scapular
abduction, which could apply undue tension to the wound.
The use of a bed trapeze is also best avoided in these
patients for the same reason.

494
ThoracicandThoracolumbarSpine:PosteriorApproach
References
t.
Freeman TB.Cahill DW. Management
of intradural
extramedullary
tu-
mors. In: Tindall GT. Cooper PRoBarrow Ot. eds. Practice
of Neuro-
surgery. Philadelphia:
Williams and Wilkins:
1996:1323-1334
2.
Levy W. Latchaw J. Hahn J. et al. Spinal neurofibromas:
a report
of 66
cases and a comparison
with
meningiomas.
Neurosurgery
1986:18:
331-334
3.
McCormick P. Post K. Stein BM: Intradural
extramedullary
tumors
in
adults. Neurosurg
Clin. Am 1990: 1:591-608
4.
Halliday
At. Sobel RA. Martuzza
RL. Benign spinal nerve sheath tu-
mors: their occurrence
sporadically
and in neurofibromatosis
types 1
and 2. J Neurosurg
1991 ;74:248-253
5.
Zide BM. Wisoff JH. Epstein FJ.Closure of extensive
and complicated
laminectomy
wounds:
operative
techniques.
J Neurosurg
1987:67:
59-64

66
OpenAnterolateral Cordotomy
DennisE.Bullardand BlaineS.Nashold,Jr.
. History
. Advantages
. Disadvantages
. Surgical
Technique
Apatientwith bilateral thoracic, abdominal, or pelvic pain
duetocanceris one of the most difficult to treat neurosur-
gically.Althoughbilateral spinal cordotomy has been per-
formedinthese patients, it runs the risk of motor weakness
involvingthe extremities or the bladder and sexual func-
tion.Becausethe pain and temperature fibers decussate in
themidline,a midline myelotomy will result in bilateral
painreliefwith minimal motor and sensory changes.
. History
Spillerand Martin in 1912,1reported on a patient with bi-
laterallossof pain and temperature due to a tuberculoma
compressingthe anterolateral quadrants of the spinal cord.
Martin,using this new information, performed the first
openanterolateralcordotomy for relief of pain.
Untilthe introduction of the percutaneous cordotomy,
theopenoperation was the treatment of choice in cancer
pain.Theopen operation had certain limitations in that it
wastechnicallydifficult, and with a bilateral operation mo-
torweaknessalong with bladder and bowel disturbances
couldbe serious complications. However, when the percu-
taneousoperation fails, the neurosurgeon should consider
theopencordotomy.Using the microscope makes the surgi-
calprocedureless daunting than it was in the past. Gybels
andSweet,commenting on the open cordotomy, state that
"[a]lthoughcordotomy is now carried out far less often than
formerly,its capability of producing a completely pain-free
state in the appropriately
selected
and fortunate
case
shouldnot be forgotten-the
more unilateral the pain the
morelikelyisa gratifying success."2
Schwartzoriginally described the open cervical cordo-
tomyin 1967 and the following account is taken from the
Schwartztechnique described in the original KempeOpera-
tiveNeurosurgery.3"Thisprocedure takes much less time
andiswell tolerated even by very sick patients. Compared
tothe technique of percutaneous cordotomy, this operation
canbe donejust as quickly and has the advantage of direct
visualization." This is especially true if the operating micro-
scope is used in the operation.
.
Advantages
. Good approach for bilateral thoracoabdominal pain sec-
ondary to cancer
.
Disadvantages
. Risk of paralysis and loss of sphincter
control
.
SurgicalTechnique
The patient is placed in the prone position with the head
slightly dependent as shown in Fig. 66-1. Localanesthesia
is used. Amidline skin incision is made from the inion to
the spineous process of C2.The muscles are stripped uni-
laterally from the spinous process and lamina of C2, the
arch of the atlas, and the posterior rim of the foramen
magnum, and the patient's head is flexed. These two ma-
neuvers will widen the intra laminar space between C1
and C2. The ligamentum fIavum is very thin at this level
and usually can be incised and reflected along with the
dura. Alongitudinal dural incision is made from the lam-
ina of C1 to the lamina of C2in the lateral one third of the
dural exposure (Fig. 66-2). Care must be taken to avoid
opening the epidural veins in the lateral gutter. The dural
margins are retracted with stay sutures. The arachnoid is
torn and cerebrospinal fluid is aspirated. The denticulate
ligament is identified and followed to the cord. This liga-
ment is left attached to the dura to prevent any distortion
of the cord. The dentate ligament is then grasped flush
with the cord and elevated slightly (Fig. 66-3).
The
495

496
ThoracicandThoracolumbarSpine:PosteriorApproach
~-
Figure
66-1
The surgical
exposure
ofthe
cervical
spinal cord as described
by Schwartz.
Figure 66-2
The cervical spinal cord with the dural
opening
over the dentate
ligament
as described
by
Schwartz.
Figure66-3
The exposed spinal cord and section-
ing of the anterolateral quadrant as described by
Schwartz.

-
66
OpenAnterolateral Cordotomy
497
cordotomyis then completed. The incision in the antero-
lateralquadrant of the spinal cord is made at a depth of 5
mm.Thesmall knife blade is introduced at the junction of
thedentate ligament and the pial surface of the cord. The
knifeblade is passed through the cord anterior to the exit
ofthe ventral roots dividing the spinothalamic tract. Acut
References
1.
Spiller WG, Martin
E. The treatment
of persistent
pain of organic
origin in the lower part of the body by division
of the anterolateral
column ofthe spinal cord.jAMA
1912;58:1489-1490
posterior to the dentate attachment
will endanger the
pyramidal tract. To include the arm the incision can be
continued 1 mm to within 2 mm of the anterior spinal
artery. When the operating microscope is used, the open
cordotomy can be done almost as quickly as the percuta-
neous cordotomy.
2.
Gybels jM, Sweet
WHo Percutaneous
anterolateral
cordotomy.
In:
Gybels jM, Sweet
WHo eds. Neurosurgical
Treatment
of Persistent
Pain. Basel: Karger; 1989: 173-179
3.
Kempe lG. Operative Neurosurgery. Vol.2. Berlin: Springer-Verlag; 1970

67
Commissural Myelotomy
Dennis E.Bullard and Blaine S. Nashold, Jr.
.
Indications
.
Advantages
.
Disadvantages
. History
.
SurgicalTechnique
.
Indications
. Bilateralpelvicor lowerextremitypaimrefractoryto all
othertreatmentswith limitedlifeexpectancy
.
Advantages
.
Offersbilateral central pain control
.
Goodresults for pelvic and visceral pain
.
Disadvantages
.
Effectiveness is time limited
.
Risk of paralysis
. History
In 1926,the commissural myelotomy was first conceived by
Greenfield but it was Armour who performed the first
myelotomy for pain in a patient with tabetic gastric crises.!
He sectioned the spinal cord in the midline using a "ball-
pointed knife"thereby avoidinginjury to the anterior spinal
artery. Armour's surgical technique is still the basis for to-
day's myelotomy.
.
SurgicalTechnique
The operation consists of dividing the spinal cord in the
midline to sever the crossing pain fibers. These pain fibers
cross over through three segments of the spinal cord before
498
...
joining the spinal thalamic tract on the opposite side.The
midline myelotomy is used to control pain from cancerin-
volving the lower abdominal and pelvic regions ofthe body.
Pain from cancer of the rectum, ovaries, and prostatehas
been relieved, in addition to pain of multiple sclerosis,
arachnoiditis, and tabes dorsalis.
The standard commissural myelotomy is performed three
levels above the highest level of the pain. In the caseof
pelvic pain, a laminectomy is done at the T7-11 level(Fig.
67-1A). The earliest myelotomy was done without the aid
of the operating microscope, which now has greatly im-
proved the visualization of the spinal cord structures. After
the dura is opened along the midline, the dorsum of the
spinalcordisidentified.Thereis usuallya largedorsalvein,
which is carefully moved laterally, exposing the midline
septum of the dorsal spinal cord. The spinal cord is then
sectioned over a distance of 25 to 35 mm. The pia arachnoid
and the dorsal septum are sectioned using a microknife
(Fig.67-1B). Ablunt microdissector is then introduced into
the depths of the midline gently sweeping it over three
spinal cord segments. The spinal cord tissue offers littlere-
sistance to the dissector and as the microdissector isintro-
duced into the depths of the spinal cord between the dorsal
columns it will meet resistance at the inner surface ofthe
pia. This pial barrier should be preserved to protect thean-
terior spinal artery, which lies beyond in the anterior spinal
sulcus (Fig.67-2A,B).
Thereis recent anatomicalevidencethat the rectalpain
fibers run in the mesial part of the dorsal columns andac-
cording to Naute et aI,2 "the cell bodies of origin in this
'new' pathway lie in the spinal ray matter dorsal to the cen-
tral canal near the base of the dorsal horn where theyare
directly or indirectly in receipt of segmental primary affer-
ents" (Fig. 67-3). Based on this new anatomical informa-
tion, Naute has modified the original midline myelotomyto
successfully treat rectal pain due to cancer by sectioningthe
medial quadrants of the dorsal columns. He calls the opera-
tion a "punctate myelotomy" (Fig.67-4).

67
Commissural Myelotomy
499
A
II
Nauta reports using the "punctate
myelotomy" in a
woman with abdominal pain due to uterine cancer. A
laminectomy is done at the 17, 8, 9 spinal levels. The dura
is opened and the dorsal root entry zones are identified.
Usingthe operating microscope, the exact midline of the
spinal cord is identified and a short rostral-caudal section
of the septum posticum is performed. A 16-gauge needle
on a tuberculin syringe is used to produce the lesions at a
depth of 5 mm. "It [needle] is inserted twice. First with the
bevelto the right. then to the left, each time to a depth of 5
Figure
67-1
(A) Exposure of the dorsal aspect
of the
thoracic spine is obtained via laminectomies from 17 to
T1l. (8) A midline dural incision isextended to gainaccess
B
to the dural aspect ofthe spinalcord.
mm. The depth could be judged accurately by first measur-
ing the bevel length (approximately 6 mm from tip to in-
tact needle shaft). The intention is to interrupt only the
most medial fibers ascending in the fasciculus gracilis"
(Fig. 67-5).
The midline myelotdmy has not been fullyutilized by the
neurosurgeon to treat the difficult bilateral abdominal and
pelvic pains. Using the Nauta technique there is now hope
to relieve the pain from the rectal region.which has been so
difficult to control.

500
Thoracic and Thoracolumbar Spine: Posterior Approach
A
B
Figure 67-2
(A) Dural sutures are utilized to expose the dorsal aspect of the spinal cord. (8) The conus medullaris and cauda equina are readily vi-
sualized
with a series of dural tenting
sutures.

67
Commissural Myelotomy
501
16 gauge
Dorsal vein
/
,
Sacral cord
Figure 67-3
Nociceptive
input
from the pelvic viscera arrives in the
dorsal horn of the spinal cord where it is relayed to higher centers by
cellsnear the central canal. These postsynaptic
dorsal horn cells send
their axons in the midline
of the dorsal column
to synapse in the nu-
cleusgracilis. The pathway then crosses the midline
in the lower brain
stemto ascend to the ventral
posterolateral
nucleus of the thalamus.
Alleviation of pelvic visceral pain in the present case was accomplished
byinterrupting
this pelvic visceral pain pathway
by making a punctate
lesion in the midline
of the dorsal column.
The punctate
lesion was
madeby lowering a 16-gauge needle into the midline
of the dorsal col-
umnto a depth of 5 mm on either side of the medial septum,
avoiding
thedorsal vein (as shown in the upper left).
Commissural
Myelotomy
Punctate
MidlineMyelotomy
:::
..;..
~rn1
I::': ::
::::
,Ii
'! Iii
J;
~ rr'
'..
;:
I t..
~
; Jt
:
':"4t ,:
:"8:.:-
~.~~
~
4.
I.
T10
From viscera
Pelvic pain
Pelvic pain
A
relief
relief
B
Figure 67-4
Commissural myelotomy hasbeen performed at vari-
ous rostrocaudallevels. (A) In the past, commissural myelotomies
were performed with the intent of eliminating crossing fibers of the
spinothalamic tract segmentally for relief of pain. In addition to lesion-
ing the portion of the spinothalamic tract crossingat the siteof the le-
sion, the commissural myelotomy would also interrupt the pelvicpain
pathway traveling in the midline. (8) Punctate midline myelotomy
eliminates only the ascendingpelvicvisceral painpathway,leavingthe
spinothalamic tract and most of the dorsal column intact.

502
ThoracicandThoracolumbarSpine:PosteriorApproach
A
B
References
Figure67-5
(A) The technique of the standard
midline myelotomy. Note the careful retractionof
the dorsal artery to gain accessto the midlineofthe
dorsal columns. (B) The section hasinterruptedthe
crossingfibers of the spinothalamic paintracts.
1. Armour D. Surgery of the spinal cord and its membranes.Lancet
1927:1
:691-697
2.
NautaJW, Haring Hewitt E,Westlund KN,Willis WDJr.Surgicalinter-
ruption
of a midline dorsal column visceral pain pathway.JNeuro-
surg 1997:86:538-542
L

68
TheDREZOperation
DennisE.Bullardand BlaineS.Nashold,Jr.
. Advantages
.
Disadvantages
.
SurgicalTechnique
.
BrachialPlexus Avulsion
ClinicalPresentation
SurgicalTechnique
Positioning
Approach
.
Avulsion at the Conus Medullaris
Chronicpains originating from lesions of the central ner-
voussystem (e.g., brachial plexus avulsion and paraplegia)
havealways resisted medical and surgical treatment. These
typesof pain are known as central or deafferentation pains.
Thedorsal root entry zone (DREZ)operation was originated
atDukeUniversity in 1976 to relieve the chronic pain from
brachialplexus avulsion injuries.! We believe that the pains
originate from the isolated central secondary sensory
neuronsin the damaged dorsal horn (Rexed layers Iand V).
Thesesecondary neurons transmit pain centrally through
the spinal cord to the midbrain, thalamus, and cerebral
cortex.
Surgical Technique
.
DREZ for Spinal Cord Injury
Clinical Presentation
Surgical Technique
.
Paraplegia
with Cyst
Surgical Technique
.
Postherpetic Pain
Surgical Technique
The principleof the DREZoperation is to destroy these
secondary central sensory neurons in the depths of the dor-
sal horn (Fig. 68-1). This is done by introducing special
DREZelectrodes (RadionicsCorp.)1.5to 2.0 mm into the
depths of the dorsal horn and producing a radio frequency
lesion of a specific time and temperature
(75-80°C for
15-20 sec). This results in a lesion of 2 x 3 mm, just large
enough to destroy the dorsal horn region and spare the ad-
jacent dorsal column and pyramidal tract, thereby reducing
possible complications.
503

504
Thoracicand Thoracolumbar Spine: Posterior Approach
,_Lesion
Electrode
.
Advantages
. Usefulin chronic, deafferentation pain
.
Goodresults in "end-zone" pain
.
Disadvantages
. Riskof paralysis
.
Potential for loss of bladder and bowel function, particu-
larlywith conus lesions
.
Poorresults in diffuse pain
.
SurgicalTechnique
Thereare certain general surgical principals that apply to all
DREZoperations.TheDREZis a major physiologicalchal-
lenge and the patient should be adequately prepared and
evaluated preoperatively. Standard steroid protocol with
methylprednisolone at the time of induction is used for all
DREZprocedures.The steroid protocol of methylpred-
nisolone during induction is maintained for 24 hours, fol-
lowed by a relatively rapid tapering of steroids over the
next 3 to 5 days. Patients are maintained in the intensive
care unit for 24 hours. Mobilization out of bed is restricted
for 72 hours because of the opening of either or both the
spinal and brain stem dura; however, range of movement
exercises and general toning procedures are done consis-
tently during this period. The bowel and bladder dysfunc-
tion and the lower extremity weakness that are present in
many of these patients must also be dealt with in a planned
fashion. At our institution, we routinely use compression
stockings and pneumatic compression devices to prevent
deep vein thrombosis. Urine cultures are obtained in the
preoperative period in all patients with dysfunctional blad-
ders so the appropriate additional antibiotics can be used as
needed. Aslong as the indwelling catheter is in place, urine
Figure 68-1
Cross-section
of the human cervical spinal
cord. Note the dorsal root entry zone (DREZ)electrode
tract and the estimated radiofrequency(RF)lesionsize.
cultures need to be obtained periodically. In general, pro-
phylactic perioperative coverage is with cefamandole, 1g
intravenously at the time of induction and 500 mg every8
hours for 48 to 72 hours. If patients have true allergy to
penicillin or cephalosporins, then vancomycin is used.Vig-
orous pulmonary management and joint mobilization are
crucial and any postoperative febrile episode is taken seri-
ously. All fever spikes are evaluated with blood and urine
cultures and chest x-rays.
We have not used anticoagulation prophylactically. The
incidence of deep vein thrombosis in this high-risk popula-
tion has been < 1%.Patients are also placed on either soft
care or pneumatic mattresses with frequent rotation topre-
vent skin breakdown. Physical therapy and occupational
therapy are key components to the team approach andare
involved from the preoperative through the acute postoper-
ative period. Because many of our patients live a distance
from the hospital, we have arranged outpatient transitional
facilities to allow graded postoperative care before release
from the area. We believe that the use of all of these tools
have been major factors in significantly reducing the mor-
bidity associated with this operation.
These patients have often developed dependence on nar-
cotic analgesics. Narcotic analgesics are progressively with-
drawn in the postoperative period but total discontinuation
is beyond the scope of the surgical period. In the postopera-
tive period it is critical that these changes be done in a slow,
controlled fashion. This is usually accomplished with a
team approach employing members of the hospital's pain
control center. It is also critical that there be an ongoingre-
lationship with the referring physician so that the eventual
maintenance of medication and multidisciplinary follow-up
can be performed in the patient's home environment. This
involves physical therapy, psychosocial support, and multi-
ple medical disciplines.
There are several types of DREZelectrodes, each designed
for a specific DREZoperation; those for the brachial plexus
lesions have a 2 mm lesioning
tip and a 0.25 mm diameter
(Radionics Corp.) (Fig. 68-2). To prevent deeper penetration
into the spinal cord a plastic collar surrounds the upper end

68
DREZOperation
505
Thermocouple
Sensor in Tip
r-U.25
mmdia.
1~ Ga. Guide
12
1
Cannula
mm
Right Angle Cauda lis DREZ Electrode
A
2.5mm
\
I
=,
1mm
}2 mm
II
I ·
Insulation
.6mm
-11.2
mm
L
dia. 0.25 mm
1
oftheexposedtip of the electrode.Asmaller 1.5mmelec-
trodetip can be used in the thoracic and conus regions
wherethe spinal cord is smaller in diameter. There are two
electrodesfor the caudalis lesions (Fig. 68-3) (see section
oncaudalis DREZ).These electrodes are very fragile, but if
operating room staff handle them carefully they will last
manyyears.It is alsoimportant forthe surgeondoingthis
operationto have a second set of electrodes and additional
connector cables. The various models of the Radionic
radiofrequency RF lesion generator can be used for the
DREZlesions.Thesurgeonand at leastone operatingroom
staffmember should be familiar with the operation of the
lesiongenerator. Every neurosurgical resident should un-
derstandthe function and the use of an RFgenerator before
goinginto practice.
. Brachial Plexus Avulsion
MotherNature could not have given us a better model of
deafferentation pain. Brachial plexus avulsion is the result
ofextreme trauma to the upper body and arm, so violent
thatthe dorsal and ventral roots are torn from their origins
in the spinal cord. A variety of traumas cause this lesion,
mostcommonly high-speed accidents in motorcycles, auto-
mobiles,airplanes, boats, and snowmobiles. The avulsion
injuryresults in a complete denervation of the involvedarm
withthe loss of all central sensory input. The arm is para-
lyzeddue to the destruction of the motor roots in a stereo-
typicfashion but there are often additional serious traumas
to the head, neck, spine, and chest, which may mask the
symptoms of the avulsion injury in the initial posttrauma
Figure 68-2
The standard DREZ electrode
made by
Radionics Corp. Note the Teflon sleeve that prevents
the
electrode
from
being
introduced
more
than
2 mm into the dorsal horn.
B
Figure
68-3
The EI Naggar right-angle caudalis DREZ
electrodes.
period. Generally the history of phantom pain can be traced
back to the earliest awakening from altered consciousness.
Thiscanbetransientbut isusuallypersistent.TheDREZop-
eration should be seriously considered if the patient contin-
ues to suffer from pain 6 months after the injury. Waiting
longer exposes the patient to possible drug addiction and
psychologicalproblems.
ClinicalPresentation
The patients classically have total paralysis of the distal up-
per extremity with intermittent
sparing of the proximal
nerves. Microreanimation procedures such as those pio-
neered by Dr. Julia Terzis have shown promise in using
these intact roots to help restore function to the extremity.
The pain syndrome involves the distal distribution or the
plexus. Generally the (6, 7, and 8 dermatome pattern is in-
volved. The patients describe the phantom arm as being
clasped to the chest or flexed. The pain is most frequently
electrical, or burning, although at times it is described as
tearing or gripping in nature. Patients frequently describe
the hand feeling as if it were holding a burning coal or hav-
ing the skin peeled off or the fingernails pulled out. The
common feature in all patients is the agonizing, suffering
component.
Superficial stimulation may exacerbate this pain, but allo-
dynia or hyperesthesia is not always present. Trigger points
may include the chest wall, proximal shoulder, or face. The
crossover with proximal facial tracts, which may extend as
far inferiorly as (6, is often evident with a facial stimulus
causing reproduction of the pain in the arm or the sensation
of a painful phantom.
Medical therapy
or peripheral

506
Thoracicand Thoracolumbar Spine: Posterior Approach
procedures, including amputation ofthe arm, are seldom of
any benefit.
Surgical Technique
Surgicalrelief of the pain is best performed prior to the re-
constructive surgery to maximize the rehabilitation period.
It is important to spare the uninvolved proximal root for
this reason. Because of the incidence of associated cervical
injuries, including fractures and delayed ruptured disks,
magnetic resonance imaging (MRI) of the cervical spine
should be done
in the
preoperative
period. Aproxi-
mately 10%of patients will have an associated cervical
lesion.
Positioning
The patient is placed in the prone position (Fig.68-4) with
the head held firmly in a head holder. The positioning is
the same for caudalis. upper thoracic, and cervical DREZ.
The bed may be tilted so that the surgeon is able to sit for
the surgery if this is preferred.
Approach
The avulsion usualIy involves at least four or five dorsal roots
((5- T1). Hemilaminectomies
sparing
the lateral elements
[=-;
A
B
are performed based upon the preoperative MRIand clinical
syndrome but generalIy extend from (4 to T1 to exposethe
dorsal surface of the spinal cord above and below the levels
of the avulsion. InitialIy, fulI laminectomies may be used
until the surgeon becomes familiar with the alterations
from normal anatomy. Byundermining the midline lamina
with the drill,the exposureto the contralateralsideisade-
quate. This exposure allows the surgeon to visualize under
the microscope both sides of the dorsal surface of the spinal
cord. The spinal cord is virtually always rotated towardthe
normal side. On the avulsed side, atrophy and changesin
the surface of the spinal cord often distort the normalspinal
cord anatomy. It is easier to discern the area of the damaged
dorsal horn if the surgeon can visualize the adjacent normal
side.
The subarachnoid space isoften thickened with strandsof
scarred arachnoid tethering the surface of the spinal cordto
the inner surface of the dura. These strands of scar tissue
needtobecarefullydividedpriorto performingtheDREZle-
sions. The initial trauma often results in the productionof
traumatic myeloceles,which can be visualized on a preoper-
ative scan.The myeloceles can extend into the intravertebral
nerve root exit region and beyond into the adjacentsoft
tissues of the neck, and at times may extend into the arm
following the course of the plexus below the level of the
clavicle. They communicate with the subarachnoid space
and are filled with spinal fluid. The myelocele can be seen
when the dura is open but should be left untouched bythe
-
Figure 68-4
The positioning
of the patient for the
DREZoperation. (A) The upper position is used for the
caudalis DREZ.(8) The lower position of the cervical
DREZin patients with brachial plexus avulsion.

surgeon.Theduralopening should be over the more medial,
normaldura if a successful primary closure is to be per-
formed.
Themajor spinal cord landmarks
for the surgeon
are as
follows:The dorsal columns are identified
first. On the nor-
malside,the dorsal roots can be seen as they exit from the
lateraledge of the normal dorsal column. This lateral edge
isidentified by a thin white line and it forms the medial
portionof the interomediallateral
sulcus from which the
dorsalrootsemerge. Each dorsal root as it exits from the
spinalcordconsists of five to seven rootlets, which originate
fromthis intermediolateral
sulcus and fuse to form the dor-
salroot. Although on the avulsed
side of the spinal
cord
theseroot structures
are missing, the lateral
edge of the
dorsalcolumn should be easily identified.
The sulcus often
containssmall, 1 to 2 mm ovoid areas of degeneration.
whichare the remnants
of the exit zones of the individual
Figure68-5
Thecervical DREZprocedure for brachial plexus avul-
sion.NotethestandardDREZelectrode on the left side (avulsion) of
thespinalcordandthe normal intact dorsal cervical roots on the right.
Theartistdrawingon the left side of the spinal cord illustrates the
DREZ
operation.Notethe lineof lesions.
68
DREZOperation
507
rootlets(Fig.68-5). TheDREZlesionsare made alongthis
lateral lineand sulcus.TheDREZlesionsshould be started
at the lower end of the avulsed region beginning just at the
upper rootlet of the lowest intact dorsal root (usually n)
seen in Fig.68-5. This starting point allows the surgeon to
visualize the spinal cord above. thereby making the place-
ment of the lesions more precise.The lesion electrode up to
the plastic collar (2 mm) penetrates the spinal cord and the
lesion produced using RFcurrent. The electrode is oriented
in a lateromedial direction with an angle of -25 degrees.
The number of lesions depends on the length of the avulsed
region. Agood rule of thumb is 10 lesions for each centime-
ter; if the avulsed region is 50 em long it will require -50
lesions. Afterthe lesioning the dura isclosed.
The electrodes for the brachial plexus lesions have a
2 mm lesioning tip and a 0.25 mm diameter (Radionics
Corp.). The electrode will penetrate these small ovoid re-
gions that are soft and degenerated. Visualizing a normal
root above (C4) or below (n)
the avulsed area will aid in
determining the line of the lesions through the avulsed re-
gion.Thedetailsof the productionof the DREZlesionsare
criticalforthe successor failureofthe DREZoperation.Itis
important to make the cervical lesions at a temperature of
75°Cfor 15 seconds. It is also important to start the timing
of the lesion only when the temperature
reaches 75°(,
When these lesion parameters are not followed serious
complications may occur. The surgeon must exercise ex-
treme care in manipulation of the spinal cord. Damage to
the surrounding structures may cause severe incoordination
or weakness of the ipsilateral leg and there have been a few
cases of paraplegia reported. The addition of steroids and
meticulous surgical technique will significantly reduce
these hazards.
.
Avulsion at the Conus Medullaris
Traumatic avulsion of the dorsal roots from the conus
medullaris is less common than the brachial plexus. The
typical history is of a severe trauma to the pelvis or leg.Sev-
eral of our patients suffered traumatic amputation of the
leg after being struck by a car as they walked along a road-
way. In the other cases, there is a history of severe pelvis
fractures with dislocation of the pelvic bones. Patients often
have evidence of trauma to the bladder and may have
hematuria. When seen months after the injury, they may
show varying degrees of leg weakness and sensory deficit
involving the lower lumbar and sacral roots.Theirinitial di-
agnosis is often pelvic plexus injury but a scan of the lum-
bosacral spine will reveal the traumatic myelocelesimilar to
those seen with brachial plexus avulsion. The myelocele is
generally at the L5or 51 spinal level but the root avulsion is
located at the level of the conus (T11-12)(Fig.68-6).
Surgical Technique
The patient is positioned in a standard fashion with chest
pads and clearance of the abdomen. The MRIand an intra-
operative x-ray localize the site of bone removal that usu-
ally extends from no
to L2.After bony removal, the bone

508
Thoracic and Thoracolumbar Spine: Posterior Approach
Figure68-6
Lumbar myelogram showing a traumatic myelocele of
the lumbar fifth root asit exits the spine; however, the avulsion is at
the levelof the conusmedullaris (T12).
edges are waxed, a small strip of hemostatic material such
as surgiseal or its equivalent is placed in the lateral gutters
and the dura opened in the midline. It is held back with
5-0 neural sutures attached to snaps to tamponade the
epidural veins. The advantage to using snaps rather than
tying the suture to the muscle and fascia is that the tension
on the suture line can be progressively increased as dissec-
tion is performed longitudinally. Wherever possible the
arachnoid is left intact until the full dural opening is ac-
complished. This prevents drainage of blood into the sub-
arachnoid space and obliteration of the anatomical sub-
tleties, which are crucial in the dissection. The smallest
amount of blood in the subarachnoid space causes major
obliteration of the structures. The arachnoid is sharply
opened under the microscope and the edges held to the
dura with microhemoclips.
Electrode recording is then done using 3 or 4 contact
electrodes with the contacts 5 mm apart, roughly corre-
sponding to the radicular fields. The input from the surface
electrodes, which are placed over the hyperpathic areas on
the lower extremities, is then done to help with localiza-
tion of the site of injury and the level of spinal cord. Fewer
of the lumbosacral dorsal roots are avulsed and when the
conus is exposed the avulsed area may not be immediately
Figure 68-7
The conus medullaris
with two avulsed dorsal roots.
visualizedbythe surgeon(Fig.68-7). Thedorsalrootsex-
iting from the conus into the cauda equina overlap and
obscure the lower lumbar and sacral roots and the siteof
avulsion. The surgeon must carefully sweep these roots
laterally with microdissectionexposingthe avulsedpor-
tion of the conus (Fig. 68-8). The hyperpathic or allodynic
area can be physiologically localized by the site of peak
waveform from peripheral stimulation ipsilaterally ifthere
is sensory input or contralaterally
if the roots are fully
avulsed.TheDREZlesionsare madeat the samelesionpa-
rameters(75°(/15sec)usinga 1.5DREZelectrode.Because
the avulsedregion in the conus is smaller,a smallerelec-
trode is used and fewer lesions are made. The lesions
should extend one to two levels above the avulsion and
the abnormal roots that often border it. Often roots that
initially appear to be normal will become clearly abnormal
following microdissection. They will tend to be dispropor-
tionately smaller and have a reddish cast to them asthey
slightly dry during the surgery. This occurs despite fre-
quent moistening with an atomizer. Abnormal roots will
also be demarcated physiologically and will have abnor-
mal sensory evoked potentials. Both of these findingscan
be subtle, however. It is crucial that all of these nerve roots
and at least one and preferably two more cephalad roots
should be included in the DREZto provide for the physio-
logical overlap that occurs. The S1 and L5roots tend tobe
larger and may serve as a general landmark.
Potential involvement of the bladder and weakness from
anteriorhorncelldamagemustbe takenintoaccountwhen
the patient has retained functioning. Thisis especiallyperti-
nent because of the smaller size of the cord at this leveland
the closer proximity of these structures. Bladder and rectal
electromyographic
(EMG) recording
is routinely done at our
institution but is still in the data accumulation and analysis
stage.

68
DREZOperation
509
. DREZfor Spinal Cord Injury
Initially5 to 20%of posttraumatic
spinal injury patients
werereportedto have long-term pain.Thisinvolvesboth
penetratingwounds and blunt injury. More recent studies
involvingthe increased survival seen with more severe
multisysteminjuries have suggested that this percentage of
patientswill be closer to 25%.These patients have a long-
termchronic pain syndrome that interferes with their life
andrehabilitation.The increasing prevalence is now a major
socialand financial problem for society. Likeother central
painsyndromes. this pain does not respond to most med-
icalandperipheral surgical procedures including rhizotomy
orneurolysis.Even limited central procedures such as cor-
dotomyhavegenerally failed.
Thepain in traumatic spinal cord injuries that responds
totheDREZoperation originates in the segments of the
spinalcordjust above the site of the trauma. This can occur
atanylevelof the spinal cord. Because of the technical dif-
ferences,conus and cauda equina lesions are dealt with
separatelybut many of the principals are the same and will
notbereiterated in this section. Aswith most posttraumatic
pain syndromes. when the severe pain continues for 6
monthsor longer. the patients should be considered for a
DREZoperation.
Figure 68-8
Traumatic
avulsion of a dorsal root (51) from the
conus medullaris.
Operative drawing
on the left shows the over-
lying
intact
dorsal rootlets
of the conus retracted
laterally
to
show the small region of the avulsion side of cord just below the
blood vessel. The drawing demonstrates
the conus avulsion after
the dorsal roots are retracted.
The inset on the right shows the
dorsal medullaris
roots. The avulsed area is visualized only when
the intact dorsal roots are carefully retracted
laterally.
Clinical Presentation
Thereare two types of pain noted in paraplegics;one is a
diffuse pain often burning in nature and involving the legs,
genitals. perirectal, and peroneal regions. This type of pain
doesnotconsistentlyrespondto the DREZoperation.Long-
term studies have suggested a substantial improvement in
this type of pain in only 20%of patients. The second type
of pain is segmental or radicular. In the segmental type,
which has been referred to as end-zone pain, there is a
zone of pain just above the area of the complete sensory
loss (Fig.68-9). The pain may involve several sensory der-
matomes. and often stimulating the skin of the dermatomes
will increase this pain. The patient is often aware of this hy-
persensitive skin zone and avoids contact with it. During
the neurological examination, the surgeon can reproduce
the pain by touching or rubbing the involved area of skin.
These pains begin immediately after the injury and are de-
scribed as burning in nature and with episodes of electrical
shocks radiating into the paralyzed legs. This type of pain
can be associated with a posttraumatic syrinx.
Patients who develop a traumatic spinal cyst have a de-
layed onset of pain. which may occur several years after the
trauma. Allparaplegics should have an MRIscan of the trau-
matic region because of this possibility. The presence of a

510
ThoracicandThoracolumbarSpine:PosteriorApproach
_
Transition
Zone
onnoAneathesla
eaPaln
A-C
cyst alters the surgical procedure. This is described in
the following section. The segmental pain is also seen in the
quadriplegic who complains of arm pain. The extent of the
lesioning will depend on the width of the painful der-
matomes, and the lesions should be extended one to two
dorsal root levels above this painful zone. This causes the
patient's
original sensory
level to rise and must be
explained preoperatively to the patient. When the trau-
matic dermatomes involve the abdominal regions no seri-
ous consequences result from this increased sensory loss. In
cervicallesions, this can be a more significant factor in deci-
sion making. Bilateral DREZlesions will be required with
bilateralpain.
SurgicalTechnique
Standard positioning and medications including steroids
and antibioticsare used. The patient is placed under general
anesthesia and positioned prone using chest and abdominal
supporting frames. The surgical field should be parallel to
the floor to minimize cerebrospinal fluid ((SF) drainage.
Partial tamponade of the field with cotton balls may help.
Preoperative MRIscans allow better planning of the incision
so that the lowest aspect of exposure will include the upper
aspect of the trauma. The opening is described in the conus
avulsion section and will not be repeated here. Again it is
crucial that meticulous dissection of the cord and roots be
performed without allowingsubarachnoid blood to obscure
the microanatomy.
It is not necessary to fullydissect the traumatic site at the
spinal cord level. Rather, this area should be the border of
the caudal dissection because further exposure of it in-
creases the risk of (SF leakage postoperative and where
there is a degree of residual cord functioning, dissection
into this area significantly increases the risk of additional
cord injury. Radiology can preoperatively mark the back so
Figure 68-9
Paraplegic patients with the three
types of pain. The "end-zone" pain is represented
in the drawing by the dark dermatomal band,
which begins at the upper level of anesthesia and
isrelievedbythe DREZoperation. Paininthedis-
tribution
of the lower extremities
and the sacral
region does not respond to the DREZ.
that a smaller incision can be made. The level should be
marked with the arms at the patient's side and up because
this subtle difference can represent one vertebral levelin
the mid- and upper thoracic area. With paraplegic cases,
sensory evoked potentials are used to help localize the roots
within the traumatic area. Full use of muscle relaxants is
therefore encouraged unlike cases where an EMGis to be
used.
After bony removal of the lamina and spinous processes
with a paring of the lateral elements, the bone edges are
waxed, a small strip of hemostatic material is used, and the
dura opened in the midline. Ifa fusion has been done previ-
ously, it should be taken down far enough laterally to allow
accessto the DREZ.It is held backwith 5-0 neuralsutures
to tamponade the epidural veins, but unlike the conus area,
if there is a fusion, tying the suture to the muscle may allow
enough extra lateral exposure to reduce the bone removal.
Snaps can be used temporarily followed by tying the suture
to the muscle and fascia as the tension on the suture lineis
increased. Oncefull hemostatis is obtained the arachnoid is
sharply opened under the microscope and the edges heldto
the dura with microhemoclips.
Electrode recording is then done using three or four con-
tact electrodes with the contacts 5 mm apart roughly corre-
sponding to the neuronal fields. The input from the surface
electrodes, which are placed over the hyperpathic areas on
the chest wall, is then obtained to help with localization of
the site of injury at the level of the spinal cord. The lesion-
ing should start at the area adjacent to the direct spinal in-
jury and extend superiorly to include one to two levels
above the area of radicular pain. The dorsal roots in this
area should be anatomically and physiologically normal.
The traumatic site of the spinal cord injury where the cord
has become adherent needs to be fully dissected at its
cephalad border. Azone of damaged rootlets can be left if
the dissection does not go down to this level. The lesions

68
DREZOperation
511
113
M6
112
111
A.A.D.I.A.L
A.A.D.I.A.L
ms
shouldbemadewith the 2.0mmDREZelectrodeat 75°Cfor
20secondsunless there is functioning cord below, in which
case15-second lesions should be made. Following lesion-
ing,the evoked potential waveform should no longer be
presentfrom the superficial areas of pain. This appears to
beacrucialfactor if complete relief from the end-zone pain
istobeachieved(Fig.68-10).
. Paraplegiawith Cyst
Thispatient population
has several characteristics
that
makeit somewhat different from the routine paraplegia pa-
tients.Thosetraumas that result in the most disruption of
thecordhave a higher incidence of long-term pain. These
aremoreoften associated with syrinx. Gunshot wounds of
thespineare the chief offenders, although a delayed syrinx
canbeseen with any injury, including relatively mild closed
trauma.Agreater incidence of pain occurs when there is a
traumaticspinal cyst.The obvious difference is the syrinx or
cyst,whichappears to be a major factor mechanically in the
painsyndrome.Manypatients haveimprovementof their
painwithdecompressionofthe cystand haverecurrenceof
thepainwhen it returns. This is not always the case, how-
ever.When the cyst dissects superiorly, the pain can extend
concurrently.Cervical pain in a patient with upper lumbar
orthoracicinjury can be caused by the extension of a post-
traumaticsyrinx superiorly. We have seen cases of cervical
painand syrinx extension up to C230 years after the origi-
naltrauma at L1.On MRI,the superior aspect of the syrinx
shouldalways be defined. Surgically this may not need to
beexposedbut is crucial for adequate follow-up.
SurgicalTechnique
PreoperativeMRIscans allow better planning of the incision
sothat the lowest aspect of exposure will include the upper
aspectof the trauma. The traumatic side itself where the
cord has become adherent
does not need to be fully
dissected.The roots exiting from the damaged spinal cord
above this however are crucial for any success. The
cystgenerallystarts at the point of injury and extends supe-
riorly.The MRIscan will allow localization of the most
Figure 68-10
Evoked potential recorded from the
dorsal surface of the spinal cord pre- and post-DREZ le-
sions. Patient suffered from an injury to the radial
nerve. The evoked potential on the left resulted from
stimulation of the involved nerve in the arm. After the
cervicalDREZ ((6,7) the evokedresponseisabolished.
superior aspect of this, which is important forpostoperative
evaluation. At surgery, the level of exposure needs to in-
clude the dermatomes involved in the painful hyperpathic
clinical syndrome and two levels above. Fulllaminectomies
are performed to allow exposure of this. The use of ultra-
sound prior to dural opening often allows excellent visual-
ization of the syrinx.
The ultrasound can also be used to help identify the cord
cystic structures, which can be poorly visualized from the
surface view of the cord (Fig. 68-11). Syrinx structures can
be central or lateral. The smallest, which may not be clearly
seen on MRI,are located along the edge of the dorsal root in
the DREZ.Asthe electrode is inserted into the spinal cord, a
small leakage of CSFand abnormally low impedance are
seen. The insertion of the electrode through this area will
often evacuate the cyst. In these situations no attempt is
made to do a midline myelotomy or to insert a catheter
within the cyst. When the cyst is larger, more centrally lo-
cated or thick walled, then midline myelotomy may be nec-
essary. Ifadequate communication with the subarachnoid
space is accomplished then no further shunting or venting
is performed. The syrinx is not specifically decompressed
until after the DREZis finished to prevent overlappingof
neural structures during the ablative portion of the surgery
(Fig.68-12).
With localizationof the syrinx cavity the DREZis per-
formed starting at the lowest identifiable abnormal nerve
root at and above the level of trauma. Conceptually, the
pain is associated with second order neurons above the in-
jury rather than the level of cord transection and dysfunc-
tion. The Radionics Corporation makes electrodes, which
extend 2 mm into the depths of the dorsal horn and
produce radio frequency lesions. These lesions are gener-
ally 2 to 3 mm. This is enough to destroy the dorsal horn
region in the normal spinal cord with syrinxes. The tissue
lesioning may be somewhat more problematic because of
the current sync provided by the syrinx and the distortion
in the anatomy. The approach to the dorsal root entry zone
is the same as with other spinal DREZprocedures. The
electrode is inserted to its hub at the level of the dorsal
root
entry
zone
and
the
lesion
of 75° for
15 to
20 seconds is made. Where there is a total loss of motor
function below a syrinx, 80° lesions had been used. Nei-
ther of these
specific parameters
has shown a clear

512
ThoracicandThoracolumbarSpine:PosteriorApproach
Figure 68-11
Intraoperative
ultrasound showinga
traumatic
spinal cyst.
benefit. Lesions are extended up into the dorsal root entry
zone above the clinical level of involvement. This generally
means including one normal
dorsal
root entry
zone
anatomically and physiologically. The ultrasound at this
point is again employed. If the cyst has been decom-
pressed and no attempt has been made to communicate it
with the subarachnoid space, either a myelotomy with full
exposure ofthe cyst or placement of small elastic tubing is
made.
Asa rule, these patients have had frequent spinal proce-
dures and the skin is often very slow to heal. When there
appears to be excessive tension on the skin or fascia at clo-
sure, we are now covering this defect with a limited muscle
flap that is rotated from the adjacent paras pinal muscula-
ture. Tension and dead space cannot be accepted at closure.
It is only when a flap is rotated that a drain is left. Other-
wise we do not leave drains because of the potential tract
formation from the dural opening.

68
DREZOperation
513
A
\
II /
J~'
\ \\
B
Figure 68-12
The spinal cord with intraspinal posttraumatic cyst. (A) The cyst enlarging the spinal cord. (8) The cyst hasbeen opened and a
drainagetube inserted. The DREZ lesions are done over the area of the spinal cord adjacent to the cyst.
.
Postherpetic Pain
Patientswith chronic chest wall pain following herpetic
infectionsbecomeDREZcandidatesifthe pain persists for
6months.This is similar to those with brachial plexus and
spinalcord lesions. In many cases, the use of antidepres-
sants,such as the tricyclics, or anticonvulsants
such as
neurontin,Carbamazepine, or phenytoin proves satisfactory
forpain control. However, in a significant number of pa-
tientsthe pain becomes a constant feature. The long-term
debilitationassociated with unsuccessful conservative ther-
apypotentially increases the risk of surgery. But there are
manycommon risk factors that make this a problematic
surgicalprocedure for thoracic postherpetic pain.
Thepatients are often older and in poor general health.
Thelesions extend over multiple thoracic levels and the
distributionin the watershed portion of the thoracic spinal
cord.Patientsover the age of65; those with underlying sys-
temic problems such
as cardiac
disease,
pulmonary
dysfunction, diabetes, or cancer; those with more than
three levels of involvement; and those with evidence of
bony kyphosis are at significantly higher risk for spinal cord
infarction. This is the major risk involved with this proce-
dure. There is also a higher incidence of ipsilateral lower ex-
tremity dysfunction because of the smaller diameter of the
cord and the potential for both anterior motor damage or
dorsal column dysfunction. This becomes a major factor in
the elderly.
Surgical Technique
The technical aspects are generally similar. Standard posi-
tioning and medications are used. Levels are ascertained
radiographically and physiologically. The nerve roots in-
volved are often smaller and reddish in color as has been
noted with the other syndromes. The exposure is generally
done with hemilaminectomies. This provides adequate ex-
posure and is associated with significantly less morbidity
in the postoperative
period. The patients
are easier to
mobilize and have less pain than when full laminectomies

~
514
Thoracic andThoracolumbarSpine:PosteriorApproach
are done.
Carefulattention must be given to the vascular structures
adjacent to the roots. Bothepidural and intradural coagula-
tion must be kept to a minimum. The electrode recording is
then done using three or four contact electrodes with the
contacts 5 mm apart, roughly corresponding to the radicu-
lar fields.The input from the surface electrodes. which are
placed over the hyperpathic areas at the lower and upper
borders on the chest. is then obtained to help with localiza-
tion ofthe site of injury and the spinal cord level.
The lesions should extend one to two levels above the ab-
normal roots. Often roots that initially appear to be normal
will become clearly abnormal following microdissection.
They will tend to be disproportionately smaller and have a
reddish cast to them as they slightly dry during the surgery
Reference
1.
Nashold BSJr. Pearlstein
RD.The DREZOperation.
Park Ridge: AANS;
1966
just as has been noted earlier. Abnormal roots will alsobe
demarcated physiologicallyand will have abnormal sensory
evoked potentials. Both of these findings can be verysubtle,
however. and are often less pronounced than seen withthe
other types of lesions. It is crucial that all of these nerve
roots and at least one and preferably two more both caudad
and cephaladshouldbeincludedin the DREZtoprovidefor
the physiologicaloverlap that occurs.
Because of the age factor, mobilization must be done
rapidly after surgery. These patients
frequently require
placement in a rehabilitation facility in the immediatepost-
operative period. The involvement and interest ofthe family
physician are also crucial if a significant improvement in
quality of life and mobility are to be obtained.

69
TheCaudalis DREZ
DennisE.Bullard and Blaine S. Nashold, Jr.
. Indications
. Advantages
. Disadvantages
. Objective
. Surgical Technique
Closure
Refractoryfacial pain is one of the hardest clinical syn-
dromesto treat.Generalmedical regimes including the use
ofnarcoticanalgesics,Neurontin, Tegretol, Elavil, and other
medicationsin conjunction with biofeedback, local blocks,
massage
therapy,andother limited invasive modalities gen-
erallyfail.Unfortunately, peripheral pain procedures such
asperipheralavulsions,ablations, and partial sections also
fail.Moreinvasivecentral procedures such as microvascular
decompressionand partial sectioning
of the trigeminal
nerveinfrequentlyprovide any relief when the mechanism
iscentralin nature. If they succeed. the original diagnosis
mustbereconsidered.
Thefailure of most regimes and the complex nature of
thefacialstructures,both centrally and peripherally, make
centralpainacontroversial topic (Fig.69-1). Our previously
mentionedprincipal-that
central pain involves the hyper-
activityof the second-order neurons in the brain stem-is
alsoapplicableto facial pain. Obviously, in these cases, the
mechanismis lesswell defined and the lesion that sends
signalstothebrain stem and on to the thalamus subcortical
groupsandcortex with the perception of pain is more a
matterofconjecture.Patients with central infarctions of the
brainstemor thalamic nuclei, multiple sclerosis, and cer-
taintypesoftumors present with such syndromes and sup-
portthegeneralhypothesis. Patients with iatrogenic central
facialsyndromesfollowingunsuccessful attempts using pe-
ripheralproceduresto treat such problems become more
complexto explain. The question of primary versus sec-
ondarycausesis one obvious point
of debate. Lastly,
trauma,eithernonspecifically with closed head injuries or
morespecificallyfollowingdental or oral procedures. is the
causeofaseverecentral pain syndrome that is difficult to
explainaswell astreat.
Patientswith central pain syndromes often have sharp or
burningpainover the face with trigger points. The overlap
withthe classic trigeminal presentation
is often subtle.
There is usually an area of sensory loss, the history of a
prior surgicalor nonsurgicaltrauma, and the failureof re-
sponse to conventional medications. The classic syndrome
of anesthesia dolorosa is not always fully present.
The dorsal root entry zone (DREZ)operation for facial
pain has been called the caudalis DREZprocedure. The early
successwith cervicalDREZprocedures for brachialplexus
avulsioninjuriesledto the use ofa similaroperationfor fa-
cial pain. The anatomy, however, is significantly different.
The electrodes used for caudalis DREZhave been re-
designedto better reflectthe complexanatomyofthe cau-
dalis nucleus and tract in the anatomical area between the
C2 roots and the obex but the concept for the procedure is
the same. Lesions are designed to provide ablation of the
cauda lis nucleus in the brain stem with an overlap of the
descending tract of the trigeminal nerve. These structures
are larger than the corresponding layers of Rexed in the
spinal cord. The crucial surrounding tracts are also more
variable and more proximate to the structures to be ablated.
The electrodes have a larger lesioning area and are also de-
signed with increased insulation to spare the surrounding
structure
such as the spinocerabellar
tracts, the dorsal
columns, and the underlying corticospinal tracts.
Mostcomplicationsare associatedwith involvementof
these other structures. The most frequently seen complica-
tion after a cauda lis DREZis unilateral ataxia from damage
to the immediately overlying spinocerebellar tract. This
occurs in 30 to 60%of postoperative patients and in the
vast majority it is mild and resolves within a few weeks
with less than 20%of patients with any ataxia 1 year after
surgery. Less than 10%of patients will have diplopia,
hoarseness of voice, or long-term loss of sensation over
the face. Ipsilateral weakness is a rare complication but
has been reported,
apparently
related to involvement
of the corticospinal tracts as they decussate at the upper
C21evel.
515

516
ThoracicandThoracolumbarSpine:PosteriorApproach
Head and Neck
Cranial
Ner ves
..!J. t..:. .~:JJJJ.
'
.,
,. .' .
.
.....
.
Indications
.
Anesthesia dolorosa
.
Postherpetic neuralgia
.
Atypical facial pain
.
Posttraumatic facial pain
.
Central pain
.
Post-cerebrovascular accident(CVA)
.
Multiple sclerosis
.
Cancer-associated
head and neck pain
.
Advantages
.
Option for refractory facial pain
.
Disadvantages
.
Transient postoperative ataxia common
.
Visual disturbances. sensory loss, and hoarseness can
occur.
.
Objective
To provide symptomic relief of pain syndromes refractory to
conventional treatment
.
SurgicalTechnique
The surgical technique includes the decision of whether or
not motor responses or sensory responses will be used for
physiological localization at surgery. For caudalis DREZpro-
cedures sensory testing is employed and muscle relaxants
Figure 69-1
Detailed chart of the innervation
of the head and neck. Note the overlappingnerve
distribution of the ear and the oropharynx.
are acceptable. After general anesthesia is induced aMay-
field head holder is applied and the patient
is positioned on
a bed with either a Wilson frame or Pronese (Fig. 69-2). It
is crucial
that the head is optimally
flexed and fixed into po-
sition
so that the neck and base of the skull are opened for
full exposure.
These structures
are horizontal
to the floorat
the time of dural
opening.
The bed may be rotated so the
surgeon can sit during
the procedure.
The surgical exposure
involves a hockey-stick incision that goes from the (2 spin-
ous process up to the edge ofthe
mastoid groove superolat-
erally. This is taken asa single flap with dissection downto
the calvarias and hemilamina of C1 and C2.Carefulatten-
tion must be given not to injure the vertebral artery atthe
Figure69-2
The head and neck regions with the incisionusedfor
the caudalisDREZ.

69
Caudalis DREZ
517
lateraledge of (1. The flap is held securely back. Using a
high-powered drill, either a craniotomy or craniectomy can
beperformed. This extends from the lateral aspect of the
occipitalcondyle up to and including the midline below the
transverse sinus. There is no reason for exposing the trans-
verseor sigmoid sinuses.The dura is opened in a curvilinear
fashionand is held back with 5-0 suture (Fig. 69-3). The
useof snaps rather than sewing the retraction sutures into
the tissue allows continued progressive retraction but is
lesscrucial than in the more caudal exposure. A hemil-
aminectomy of (1 is required. It is also necessary that the
inferioraspect of the (1 lamina in the midline and the sub-
occipitalbone in the midline be undermined enough to al-
lowexposure of the midline structures, including the obex
(Fig.69-4). Bleeding is controlled with bone waxing and
thebipolaring of small bits of hemostatic material along the
bonyedge.Themaintenanceofthe arachnoid,however,is
moreimportant and an intact arachnoid should be main-
taineduntil the dural opening is completed. The subsequent
stepsin the exposure should not be undertaken if there is
anybleeding present. This is a point that cannot be overem-
phasized.The meticulous nature of the ultimate dissection
requiresa blood-free environment.
This exposure when
completed
should provide full
visualizationand access to the following structures: the (2
dorsalroots inferiorly,the spinal accessory nerve, the verte-
bralartery, the cerebellar tonsil, and the floor of the fourth
I
(
/
);.
,)
./
.'
Figure69-3
The bony and dural opening for the caudalis DREZ.
Figure 69-4
The opened dura exposing the cerebellum and the cer-
vicomedullary junction.
Note the dorsal root of C2 and the spinal ac-
cessory nerve with its individual rootlets originating
from the side of
the cervical cord. The caudalis nucleus lies in the small zone between
the (2 dorsal root and the origins of the spinal accessory rootlets.
ventricle. The obex and the (1 ventral roots should be ex-
posed through meticulous microscopic dissection. There is
often significant distortion of the anatomy when there has
been a vascular event, multiple sclerosis, or a tumor in-
volved. The surgical field must be absolutely free of blood
before any recording or lesioning is attempted.
Oncethe structures have been identified a recording elec-
trode with three to four contacts is placed on the surface of
the brain stem. Peripherally stimulating
electrodes are
placed in the distribution of the three trigeminal divisions.
The platinum electrodes are placed along the course of the
supraorbital nerve, the infraorbital nerve, and the mental
nerve to provide general input as to where these structures
are located within the trigeminal tract in the upper brain
stem. Stimulation at each of the points is then recorded
(Fig. 69-5). Our general experience has been that the 1 in-
put is virtually always between 5 to 10 mm below the obex
and a band extending down to the upper edge of the (2
fibers. The 2 input is at a narrow band extending up from
this point to the edge of the obex and is generally within
3 mm to either side of the obex.The 3 input and minitrigger
points appear to have maximal waveforms at or above the
obex. This is extended as high as 15 mm above the obex.
The exact relationship between ablation of these signals
and relief of facialpain, however,is less clear.
After recording, lesions are made with the caudalis nu-
cleus electrodes (Fig.69-5). There are two of these that are
right angled and allow for more anatomical shaping of the

518
ThoracicandThoracolumbarSpine:PosteriorApproach
+ Synchronousafferent volley
in TR1lon normal side
A
+ Asynchronousafferent volley
in TR1ldue to previous
trigeminal rhizotomy
on abnormal side
Figure 69-5
Patient with intractable facialpain
after a failed percutaneous
rhizotomy. Evokedpo-
tential recording made at the time of the caudalis
DREZ operation.
Stimulation
of the peripheral
branches of the trigeminal nerve Vl, 2,3 onthe
surface of the face and recording the evokedpo-
tential
from
the
dorsal
surface
of the cervi-
comedullary
junction.
c
+Portial reversalof negative
wavewith depthelectrode
belowgeneratoron
abnormalside
lesions. Lesions are made at 75°( for 15 seconds. The shorter
electrode,
which has a black covering, is inserted
along the
dorsal root entry zone just above the (2 rootlets. Following
the dorsal root entry zone superiorly can see this. Ten lesions
are made, each 1 mm above the other (Fig.69-6). At this
point the longer caudalis DREZelectrode is usedtocomplete
the lesioning. This deeper electrode
allows insulated cover-
ing to protect the spinocerabullar
tract on the surface ofthe
A
I
('
\
'"
A
\
~
.;; ~)
,
~"-",
r
Figure
69-6
The operative exposure for the caudalisDREZ.
Note the right angle DREZelectrode on the circular insert.Note
the line of the lesionsjust below the caudalisDREZelectrodeand
its relationship to the cervical dorsal roots and the spinalacces-
sory rootlets. Inthe upper left circular insert, the electrodecanbe
seen as it is introduced into the spinal cord with the tip of the
electrode in the caudalisnucleus.

69
CaudalisDREZ
519
brainstem.It must be inserted perpendicularto the brain
stemand it must be inserted so that the hub is in contact
withthe brain stem. otherwise the uninsulated portion of
theelectrodewill cause lesions within the superficial spin-
ocerabullartract and produce an ataxia postoperatively. The
angleof lesioning extends along the projected tract of the
dorsalroot entry zone. as shown in the figures.The shape of
thecaudalis nucleus is roughly that of a tadpole with some
variationwithin each brain stem (Fig.69-7). It angles down
ventrallyand should be sitting slightly above the spinal ac-
cessoryrootsas the obex is approached. The nucleus cunea-
tuscanoften be seen through the indentation noted with le-
sioning.
Generally-30 lesions are made depending upon the area
ofpain.When pain is in a VI or V2origin. fewer lesions are
made.We have made lesions extending as high as 15 mm
abovethe obex for oral and V3 pain; however. upon review
itappearsthat this technique results in increased complica-
tions.Althoughthe input from the V3 and oral distribution
onthe face appears to come into the spinal cord to evoked
potentials higher than the obex, it is not necessarily a
AccesSOlY
N
Tract V
_ Nucleus
Caudalis
C,
J.18mm
t".
;
,
_Spinal Tract V
.Nucleus Caudalis
D.S.CT
'-
_Corticospinal Tract
"
Dorsal View
Cervicomedullary
Junction
higher success rate in the ablation ofV3 or oral pain is not
seen with extending the lesions higher. The ablation of the
prelesion evoked potentials is usually associated
with
short-term relief of pain but does not appear to correlate
with long-term recurrence ofpain.
Closure
Meticulous hemostasis should be attained to avoid epidural
hematoma. Wound closure should be performed in multiple
layers to avoid cerebrospinal fluid leakage. The dural layer
should be closed tightly with nonabsorbable 4-0 suture. In
some cases. adjuncts such as collagen sponges and fibrin
sealant can be used to help seal the dura. If necessary. a
dural graft may also be sewn into place.Overlyingmuscular
and fascial layers can be closed with absorbable or a combi-
nation of absorbable and nonabsorbable suture in mutiple
layers. Finalskin closure should include interrupted subder-
mal absorbable suture and either a running or interrupted
epidermal nonabsorbable suture. Sterile occlusivedressings
can then be applied.
DSCT
Figure 69-7
The anatomy of the sensory and motor tracts at
the cervicomedullary
junction.
Note the shape and size of the
caudalis nucleus (in red). The nucleus is smaller in cross section
at the level of the (2 dorsal root and as it ascends rostrally to the
region
of the
obex the
caudalis
nucleus doubles
its cross-
sectional diameter. This difference in size is the reason for using
the two different types of caudalis DREZelectrodes
to insure
that the nucleus is destroyed
at the various spinal levels. Note
the close proximity of the cortical spinal tract. which must be
avoided in the lesioning.

520
ThoracicandThoracolumbarSpine:PosteriorApproach
Suggested Readings
1.
Gybels JM, Sweet WHo Neurosurgical
Treatment
of Persistent
Pain.
Basel:Karger; 1989
2.
Spiller WG, Martin E. The treatment
of persistent
pain of organic ori-
gin in the lower part of the body by division
of the anterolateral
col-
umn ofthe spinal cord.JAMA 1912;58:1489-1490
3.
Schwartz HG. High cervical
cordotomy:
technique
and results.
Clin
Neurosurg 1960;8:282-293
4.
Nashold BSJr, Pearlstein RD.The DREZOperation. Park Ridge: MNS; 1966
5.
Bullard DE, Nashold BSJr. The Caudalis DREZfor facial pain. Stereotact
Funct Neurosurg
1997;68:168-174
6.
Bullard DE, Nashold BSJr. Impedance
recording
in functional neuro-
surgery. Stereotact
Funct Neurosurg
1998;98:949-953
7.
Bullard
DE, Nashold
BS Jr. Caudalis
nucleus
DREZ for pain. In:
Youmans JR, ed. Neurological
Surgery. In press

70
Syringopleural Shunting
Jean-PierreFarmer and Gilles Bertrand
. GeneralShunting Indications
. Indicationsfor Syringopleural Shunting
. Contraindications
. Advantages
.
Disadvantages
.
RadiologicalEvaluation
. SurgicalTechnique
Anesthesiaand Positioning
SkinIncision and Musculocutaneous
Flap
Althoughsyringomyelia
has long been recognized
as an en-
tityl.2and has been surgically
managed
for over 100 years,3
itsexact pathogenesis
remains
unclear and perhaps
multi-
factorial.4-12Consequently,
several
surgical
interventions
havebeendesigned to treat it over the last decades, but it is
onlyrecently,with the development of magnetic resonance
imaging(MRI),that a true analysis of treatment
impact has
beenmadepossible.13.14MRIhas had two additional points
ofimpact on this disease: First, it has allowed earlier, nonin-
vasivediagnosis and, second, it has allowed the condition
to
bedetected in a larger number of individuals.
MRI, perhaps,
offersan opportunity to the neurosurgeon not only to re-
ducethe size of the cavity but also to correct the sympto-
matologyin a larger number of patients.
. General Shunting Indications
Causesofsyringomyelia are listed in Table70-1. It remains
primordialin treating this condition to treat the cause of
thesyrinxrather than to drain the cavity. Shunting is indi-
catedwhen there is no clearly identified treatable cause, if
treatment of the cause has failed to reduce the syrinx in a
particularpatient, or, ultimately, if the treatment of the par-
ticularcauseofsyringomyelia has been known to fail on the
basisofgeneral experience (Fig. 70-1). Forexample, a pa-
tientwith a holocord syrinx and an intramedullary tumor
nodulecan be treated adequately by removing the tumor.
Thesyrinxwill secondarily decompress in most cases and
notrecur.Similarly,a patient with a Chiari I malformation
Laminotomy
Unilateral Laminectomy (an Alternative Exposure)
Intraoperative
Ultrasound
Catheter Preparation
Approaching the Syrinx
Postdrainage Ultrasound
Laminoplasty
Closure
.
Postoperative Care
and a holocord syrinx will respond well to a Chiari decom-
pression in most casesl5-18with a gradual collapse ofthe sy-
rinx without the need for shunting. On the other hand, a pa-
tient with myelodysplasia, shunted
hydrocephalus, and
syringomyelia related, at least partly, to a Chiari IImalfor-
mation is clearly less likely to respond to a decompression
for several reasonsY First, the ability to reestablish circula-
tion of cerebrospinal fluid (CSF)at the craniovertebral junc-
tion is less given the marked subarachnoid adhesions found
there (Fig. 70-2). Second, perimedullary
adhesions and
arachnoiditis found along the spinal axis may be contribut-
ing to maintaining the syrinx full (Fig. 70-3). Therefore,in
such a situation, if there is no symptomatology attributable
to the hindbrain and if the operative goal is to treat the sy-
rinx, consideration could be given to a shunting procedure
(Fig.70-1). This procedure may be chosen becauseof its ef-
ficiency at controlling the syrinx and its lower morbidity,
given that often the syrinx can be shunted below the cervi-
cal enlargement in a patient who may have a significant
premorbid paraparesis related to the spina bifida. Hand
Table70-1
EtiologyofSyringomyelia
1
Idiopathicconditions
2
Craniovertebraldissociation
3
4
5
6
Spinal tumors (intramedullary/extramedullary)
Tethering spinal lesions
Postinfectious conditions
Posttraumatic conditions
521

522
Thoracic and Thoracolumbar Spine: Posterior Approach
Figure 70-1
Treatment decisional tree for syringomyelia; priority should be given to treating the cause whereas shunting should be reservedfor
idiopathic or treatment failure cases either in the patient to be treated or in general for a particular cause (e.g.. myelodysplasia).
A
""""'--_
L-.
--L
_ pr:---
I B
Figure 70-2
(A) Intraoperative
photograph
of Chiari Imalformation with translucent
cord over syrinx. (8) Intraoperative
photograph
of ChiariII
malformation showing abundant subarachnoid
scarring and cervicomedullary
kink. Ability to reestablish cerebrospinal fluid circulation at craniover-
tebral junction is much better in (A) than in (8).

70
Syringopleural Shunting
523
Figure70-3
Intraoperative photograph of thoracic spine in patient
with myelodysplasia.Notethe massiveperimedullary adhesionsoblit-
eratingsubarachnoid space and preventing
recognition
of underlying
cord anatomy.
function,whichiscriticalto these patients' autonomy,can
thereforebe treated without being placed at risk.
Similarconsiderations can be given to a patient with a sy-
rinxrelatedto a split cord malformation or other congenital
tetheringconditions, which is either very large in cross-
sectionalarea, expanding the cord, or persisting after the
tetheringhas been relieved.
Finally,idiopathic, postinfectious or posttraumatic
sy-
ringomyeliamight be optimally treated with a shunting
procedurein addition, in the latter, to the release of per-
imedullaryadhesions.
. Indicationsfor Syringopleural Shunting
Asyringopleuralshunt can be inserted to treat a syrinx that is
refractoryto conventional management
such as Chiari decom-
pression,totreat an idiopathicor posttraumatic syrinx,to treat
arelativelyshort syrinx where previous syringosubarachnoid
shuntinghas failed, and to treat a larger holocord syrinx asso-
ciatedwith the Chiari IImalformation. The main indication we
havehad has been the treatment
of holocord syringomyelia in
relationto Chiari IImalformation
and myelodysplasia
where
moreconventional approaches tend to fail.13
Inthis particular circumstance,
the treatment
failure may
be related to the inadequacy
of the subarachnoid
space to
absorbthe syrinx fluid (Fig. 70-3), to the frequent
blockage
of syringosubarachnoid
shunts
related
to the very small
pressuregradient favoring drainage, or, even in the case of a
patent tube, to the relatively
high resistance
to drainage
of
the tube in the context of a Valsava's maneuver
in a patient
whose syrinx has not initially collapsed well.
Syringopleural
shunting,
which
does
not
require
an
adequate recipient subarachnoid
space and which tends, be-
cause of the negative pressure
transmitted
to the syrinx, to
activelylead to a collapse of the syrinx, has been shown to be
agood treatment
option for certain cases of syringomyelia.13
.
Contraindications
. Patientswithsignificantpasthistoryofpleuraldiseaseor
reducedrespiratorycapacitymaynotbeidealcandidates.
. Advantages
Rapid collapse of syrinx
Results tend to be long-lasting
Does not require repositioning the patient
Pressure gradient between the syrinx and the pleura
may favordrainage
.
Disadvantages
Dislodgement of the catheter by the scapula is more
common.
"Daughter" cavities may form if the cavity collapses
around tube.
Negative pressure can lead to low-pressure headaches.
Exitingshunt tube may interfere with future spinal pro-
cedures
Largepleural effusion can develop (Fig. 70-4), very rare
Pleuritic chest pain for several days to weeks after the
insertion
Figure 70-4
Chest x-ray of patient with syringopleural
shunt for idio-
pathic holocord syringomyelia
showing large pleural effusion. Ultimately,
shunt was revised to syringoperitoneal
format with good outcome.

524
ThoracicandThoracolumbarSpine:PosteriorApproach
. Radiological Evaluation
The radiological assessment should concentrate on deter-
mining the cause of the syringomyelia and evaluating its
rostrocaudal extent as well as its maximal cross-sectional
diameter.Thismay require a gadolinium injection to ensure
that there is no occult neoplasm. In a patient with shunted
hydrocephalus, the patency of the shunt must be ascer-
tained. This implies visualization of the ventricular system
and may require adjunct examinations such as a nuclear
shunt-o-gram, if on clinical and/or conventional radiologi-
calgrounds, the shunt function is equivocal.
The preferred site of insertion has to be determined by
looking at the sagittal and axial images and taking into
consideration
the clinical status of the patient and the
type of shunt being inserted. Generally, if the syrinx is
wide in the upper thoracic area, below the cervical en-
largement, this is the preferred site. In these circum-
stances the syrinx is threatening
hand function but the
surgical treatment
is not because the proposed site of
myelotomy is more caudal. Additionally, this is where the
distance between the myelotomy and pleural entry sites is
the shortest.
. Surgical
Technique
Anesthesia and Positioning
General anesthesia with a single-lumen tube and minimal
positive pressure ventilation is used. There is no need to
collapse the lung during this procedure. The patient is posi-
tioned prone on chest rolls. It is important to leave ade-
quate spacing to decrease intra-abdominal pressure so as to
avoid engorging epidural veins. If the chosen site for the
syringostomyisabove T6,particularly in adults, a horseshoe
or head pin fixation may be necessary to make sure that
the spine iswell aligned and that the midline approach will
be as perpendicular as possible to the interpedicular plane.
Considerationhas to be given to possible kyphoscoliosis as-
sociated with this condition and it may be necessary to lat-
erally flex the table to secure this plane. Ifat all possible,
particularly in young children, the C7 and T1 arches and
spinous processes should be left intact to reduce the risk of
late kyphoscoliosis.Thejunction of the hypermobile cervi-
cal segment to the relatively fixed thoracic segment is par-
ticularly vulnerable to this late complication. The C7and T1
spinous processes, together with the posterior elements of
(2, act as pillars of a suspended bridge in relation to the
cervical paraspinal muscles. In turn, the latter stabilize the
cervical spine.
The incision length should correspond to three laminar
levels because this is usuallywhat is required to obtain ade-
quate exposure. The center of the incision should be deter-
mined by analyzing the syrinx characteristics on the MRI.
Fora holocord syrinx, the T2-T4segment is usually chosen
for the reasons already given.
The pleural entry site is established by determining the
maximal passive excursion of the scapular tip caudally and
planning the surgical incision above the rib that is beyond
Figure 70-5
Intraoperative photograph showingplannedlamino-
tomy
and pleural entry
site incisions.
The shoulder is mobilized
passively to find the lowest point of excursion of the scapula. Aninter-
costal space below the point of maximal excursion, in line withthe
scapular tip, is chosen.
the maximumexcursionofthe scapulartip (Fig.70-5).This
will reduce the risk of the patient inadvertently dislodging
the catheter postoperatively. It will also reduce the riskof
irritation from the catheter in relation to scapularmove-
ments.
Skin Incision and Musculocutaneous
Flap
Laminotomy Site
Respecting the midline is key when approaching the poste-
rior spine. After obtaining skin hemostasis, the remainderof
the approach should be bloodless if the muscle planesare
avoided. Byincising the spinous process cartilage,particu-
larly in children, and reflecting it laterally, one entersthe
subperiosteal
plane medial to the muscles and thereby
avoids vascular structures. Reflecting the cartilage canbe
done with a small osteotome. This subperiosteal planecan
further be developed with twisted dry sponges and small
periosteal elevators. Persistent fascial attachments canbe
released with Metzenbaum scissors and the wound canbe
kept open with a self-retainer retractor. It is good practice
to verify at this point that the depth of the exposure is sym-
metrical between the two sides and that no rotational
deformity is present as a result of scoliosis.
Pleural Entry Site
The site of pleural entry is usually above the eighth or ninth
rib on the right side. There is no contraindication
to using
the left chest pleura as well. This may be necessary ifa cor-
rective spinal instrumentation
surgery is contemplated for
the future to deal with the associated
scoliosis that mayco-
exist. In those circumstances,
the convex side of the scolio-
sis should be free of a shunt, which might interfere with ac-
cess for the instrumentation.
The skin incision is done
parallel to the rib and is offull thickness.
The length of the
incision is usually 2.5 cm. The skin is kept retracted with a
self-retaining retractor. The rib is then palpated with the

.
70
Syringopleural Shunting
525
indexfinger and the fascia as well as intercostal
muscles are
incisedwith a diathermy needle to reach the subperiosteal
spaceofthe identifiedchosenrib.Aperiostealelevatoris
thenusedto reflectthe periosteum from the rib upward.
Thetopportion of the rib is selected to avoid injury to the
neurovascularbundle. This periosteum then merges with
theparietalpleura in the interspace. Asmall punch is used
to"nibble"at the rib, removing bone the size of half a dime
to further allow visualization of the interspace. Usually,
withoutfurther retraction of ribs, the space available is such
{hatwitha no.9 Rhotondissector and with small microscis-
sors,the parietal pleura of the lung can be opened suffi-
cientlytopassthetube.Oncea smallorificeis madeinthe
parietalpleura, the lung can be seen moving with respira-
torymovementsthrough the exposure (Fig.70-6).
Laminotomy
Alaminotomywith a high-powered drill is optimal to re-
ducetherisksof late spinal deformity in children.Three
levelsareneeded because of the rather acute caudal angle
ofthespinous processes in the thoracic spine making the
hingeanglebetween the last intact vertebra and the first
sawedlevelfar less than 90 degrees. The interspinous liga-
menthas to be sectioned just below the lowest spinous
processincluded in the laminotomy. With a small curette,
theligamentumfIavum has to be disengaged from the un-
dersideofthe lamina to allow the footplate of the saw to be
franklyepidural.Given the underlying cord expansion, this
hastobedone with care. The vector of force should never
bedirectedtoward the spinal cord, but rather side to side,
gentlyelevatingthe lamina. Giventhe overlapping nature of
thelaminaein the thoracic area, it is often best to rongeur a
narrowpassagein the lamina forthe curette on each side
untilthe ligament yields with a gentle push from the
curetteagainst the undersurface of the arch. The ligament
needstobe freed completely from left to right so as to allow
swiftupwardmobilizationofthe bone flapin the event of
Figure70-6
Pleural entry site showing partially rongeured
rib and
parietallung pleura opening through which the underlying lung can
beseen moving.
brisk epidural bleeding. Strips of Gelfoam and cottonoids as
well as bone wax and the bipolar cautery should be readily
available to control brisk epidural bleeding, which could oc-
cur during elevation of the bone flap. The laminotomy
needs to be wide enough to allow visualization of the root
entry zone bilaterally. Small holes need to be perforated at
each level on each side of the laminotomy saw line and in
the spinous process to obtain a three-point fixation at each
level when reattaching the posterior elements once the pro-
cedure is completed. Epidural fat, if present, can be coagu-
lated and tucked laterally with small strips of Gelfoam.The
caudal most spinous process hole is used with a heavy su-
ture to hinge the laminotomy flap cephalad. Usually,the su-
ture is anchored using the self-retaining retractor. The flap
is then wrapped with a bacitracin gauze for the duration of
the microsurgery.
Unilateral Laminectomy (an Alternative Exposure)
It is often possible, from clinical observations and from
analysis of the axial views of the syrinx on MRI,to deter-
mine preoperatively on which side of the cord the syrinx is
largest and most likely to reach the cord surface at the dor-
sal root entry zone. In older children or in adults, a unilat-
erallaminectomy Ilaminotomy can give adequate exposure
to the dorsal half of the cord one wishes to reach. Two or
three laminae are removed on one side going as far laterally
as the articulating facets without damaging them and going
as far medially as possible, even undermining the spinous
process using bone punches, rongeurs, or drills. In fact, the
base of the spinous process on the opposite side can be
rongeured enough to allow the spinous process to be tilted
away by finger pressure causing a "green stick" fracture at
the junction ofthe remaining lamina (Fig.70-7).
This will allow for a dural incision to be made off center,
directly over the root entry zone rather than on the midline.
At the end of the procedure, the spinous processes and their
interspinous ligaments together with the attachment of the
muscles on the opposite side are still intact and, if the spin-
ous process has been fractured, it can be realigned easily
and will heal solidly in a short time.
Intraoperative Ultrasound
This adjunct has an important role during the surgery. Per-
forming a transdural examination will allow confirmation
of the volume of the underlying syrinx (Fig. 70-8). This is
useful in both the sagittal and the axial planes. In the case
of a rapidly tapering short syrinx, in particular, one ideally
would like to select a point of entry as caudal as possible
within the segment of maximal expansion so as to have as
much of the catheter within the cavity as possible. Yet, if
the myelotomy site is too low, where the syrinx caliber is
small, the risks of neurological injury are significantly
higher. If,in cross-section, the syrinx is eccentric, this can
be confirmed with assurance on the ultrasound. Finally, if
the exposure is inadequate, a decision to lengthen the
laminotomy can be made prior to opening the dura. This
will avoid risking contamination of the subdural and sub-
arachnoid spaces with blood from superficial planes.

526
Thoracicand Thoracolumbar Spine: Posterior Approach
CatheterPreparation
A reduced-tip cardiac catheter (Medtronic-PS Medical)is
used. Care must be taken to cut the distal slit valvessoasto
allow flow in a retrograde fashion from the reduced tipto-
ward the more standard-size portion of the catheter.Addi-
tional holes are placed in spiral fashion along the catheter.
but absolute care must be taken at this stage to ensurethat
all holes made in the catheter with a small rongeur willbe
buried in the syrinx. If some of the additional holesliein
the subarachnoid space, then negative pressure will be
transmitted to the subarachnoid space from the pleuraand
this may lead to low pressure headaches, aggravationof
hindbrain symptomatology, or even interference with an
existing ventriculoperitoneal
shunt in place.19Atthe distal
end, the catheter is left at full length until the amount
needed to insert in the pleura can be determined.
Approaching the Syrinx
Figure 70-7
(A)"Greenstick" fracture of spinous process inhemi-
laminectomytechnique to (8) widenthe exposure.
Once the appropriateness of the level is confirmed, thedura
can be opened with hook and a no. 11 scalpel, takingcareto
preserve the arachnoid. The dura is retracted using4-0 silk
retention sutures. Fora very lateral exposure, to identifythe
root entry zone, the sutures
can be passed
in the reflected
muscle planes under some degree of tension to widenthe
dural opening.
The microscope
is then
introduced
and the arachnoid
membrane opened in a linear fashion. It is then reflected
against the dura with surgical clips. This is a critical step be-
cause, at the end of the procedure,
the arachnoid
edge will
be incorporated
in the dural suture
line and the subarach-
noid space will thereby be reconstituted
in the hopeof
reducing the development
of perimedullary
adhesions.
Figure 70-8
Intraoperative ultrasound in
(A)axialand (8) sagittal viewsshowingthesy-
rinx. Acatheter is visualizedechographically
on the left whereas the position ofthe taper-
Bing
end ofthe syrinxisvisualizedon the right.
A

70
SyringopleuralShunting
527
Carefulanalysisofthe positionofthe rootentry zone in
relationto the ultrasound findings (central vs eccentric sy-
rinx)willthen allowthe surgeonto selecta midlineentry
orarootentry zone approach to the syrinx. The topography
ofthedorsal cord vessels then has to be analyzed. An area
devoidofbloodvesselsshouldbe selectedalongthe mid-
lineorrootentryzone and, if this is not possible,an area
witha paucity of blood vessels over the caudal end of the
dilatedsegment of the syrinx should be used. The pia may
needtobecoagulatedwithbipolarcauteryand incisedwith
afreshscalpel blade at a length of 2 to 3 mm. Rhoton no. 6
and7dissectors can be helpful to perform the myelotomy,
butmostoften, gentle dissection with the tips of a bipolar
forcepsissufficient and frees one of the surgeon's hands to
allowintroduction of the catheter once the syrinx has been
entered(Fig. 70-9). The catheter is allowed to gradually
"float"up the syrinx, usually well beyond the exposed cord
level.Gentleaspiration with a syringe and blunt needle will
confirmanintracavitarypositionbyproducinga visiblere-
ductionin cord caliber. It is anchored in a secure fashion
with6-0 Vicrylsutures to the pia, by passing the suture
throughthe catheter wall. It is also anchored with 4-0 su-
turestothe dura at its exit site. The exit from the dural tube
canbe done either using the reduced tip portion of the
catheteror using the more standard catheter diameter size.
The dura is closed with a running 4-0 PDSsuture. To pre-
vent kinking of the tube at the dural exit site, it is useful to
allow the tube to detour around the first caudal intact spin-
ous process. This allows the tube to exit in a direction that
is more parallel to the axis of the spinal canal and then to
gently curve around the spinous process before reaching
the subcutaneous layer.
It is also important to anchor the catheter at a third site in
the fascia either with an extraluminal right angle clip and
sutures by placing a right angle connector in the tube after
interrupting it or by placing a small valve or a small reser-
voir to avoid catheter migration giventhe close proximity of
the catheter pathway to the very mobile scapular region.
We favor a "spliced in" right angle piece to an extraluminal
clip because catheters have migrated despite this latter at-
tachment. We also prefer the right angle spliced connector
insertion to a reservoir or valve because patients complain
that the latter are felt when they are supine.
The two incisions are then joined by a subcutaneous
passer, which allows positioning the distal end of the
catheter from the spinal incision to the chest wall incision.
The catheter at the rib site is then cut to allow -10 cm to be
placed into the pleura. Shorter catheters can pull out with
breathing and chest movements whereas longer catheters
can cause pleuritic chest pain.
Figure 70-9
Exposeddorsal aspect of spinalcord un-
der microscopeafter arachnoidreflection showing mid-
line myelotomy kept open with bipolar forceps in the
surgeon's left hand whilethe surgeon canulates the sy-
rinxwiththe catheter usingthe right hand.

Postdrainage Ultrasound
528
ThoracicandThoracolumbarSpine:PosteriorApproach
An ultrasound examination can be done prior to reposition-
ing the bone or prior to closing the dura. The advantage of
this postdrainage study is to ascertain the catheter position
within the cord and to confirm that the syrinx has indeed
reduced in size prior to closure. The catheter position is best
determined by the axial images (Fig. 70-8), and the col-
lapse of the syrinx can be determined with both sagittal and
axial planes.
Laminoplasty
The laminoplasty is then initially secured by passing 3-0
PDSsutures through the laminar holes and letting these su-
tures hang on a hemostat. Prior to tightening them, a fibrin
glue can be applied epidurally to reduce the risk of (SF
leakage. The 3-0 PDSsutures are then tightened so as to al-
Iowa very close contact of the bone edges on one side and
more loosely on the opposite side to maintain the posterior
elements suspended at that level (Fig.70-10). This strategy
Figure 70-10
Athoracicvertebra showingthe laminardefects from
the laminotomyand the three-point fixation at the time of lamino-
plasty.Notethe closerreapproximation of bone on one side to allow
more completehealingofat leastone ofthe two fracture lines.
References
1.
Estienne
C. La dissection
des parties
du corps humain.
Paris: Simon
de Colines:
1546:3-42
2.
Ollivier
CPoTraite de la moelle
epiniere
et ses maladies:
contenant
I'histoire
anatomique,
physiologique
et pathologique
de ce centre
nerveux
chez I'homme. Volt. 2nd ed. Paris: Crevot: 1827
3.
Abbe R, Coley WB. Syringo-myelia,
operation-exploration
of cord-
withdrawal
of
fluid-exhibition
of
patient.
J
Nerv
Ment
Dis
1892:17:512-520
4.
Aboulker
J. La syringomyelie
et Ie liquides
intra-rachidiens.
Neu-
rochirurgie
1979:25:1-144
5.
Ball
MJ,
Dayan
AD.
Pathogenesis
of
syringomyelia.
Lancet
1972:2:799-801
allows the fracture line to heal in continuity at least very
well on one side. Bonybridges usually form on the opposite
side. Athird point of fixation is then obtained with 3-0 PDS
sutures by using the spinous process holes and passinga
figure-of-eight suture through the periosteum reflected
with the muscle plane to encourage osteogenesis overthe
fracture lines. This also stabilizes the laminotomy flapvery
significantly.
Closure
The superficial wound is then closed with inverse inter-
rupted 3-0 Vicrylsutures passed through the fascialplanes
and through the subcutaneous planes. Toreapproximatethe
skin. 4-0 monocryl subcuticular sutures and Steristripscan
be used. The closure at the pleural site involves fascialclo-
sure with a purse-string suture being placed in the muscle
plane to avoid air from being sucked in and to further stabi-
lize the catheter. The fascial plane is then closed uniformly.
The subcutaneous plane is also closed with 3-0 Vicrylinter-
rupted sutures whereas 4-0 monocryl subcuticular sutures
and Steristrips reap proximate the skin. Both wounds are
then covered with a dry dressing.
.
Postoperative Care
In the recovery room. patients are examined to ensure that
their posterior column and motor functions are preserved.
They will also be monitored in the postoperative phasefor
sphincteric function. A standard chest x-ray will be ob-
tained to confirm the position of the tube. both along the
spinal axis and in the chest. Additionally. the presence ofa
pneumothorax can be ascertained on the film. The patient
will be allowed up the next day. If the incision is inter-
scapular. maneuvers that produce scapular winging willbe
contraindicated for several weeks. In particular. the patient
should be discouraged from turning from side to side inbed
by pulling on the bed rails with the hands because this puts
great stress on the suture line of the muscle and fascia.
These precautions allow maintaining a narrow scar at all
levels of closure. Acontrol MRIexamination should be per-
formed.
6.
Gardner WJ. Hydrodynamic mechanism of syringomyelia: its rela-
tionship to myelocele. J Neurol Neurosurg Psychiatry 1965:28:
247-259
7.
Gardner WJ,AngerJ.The mechanism of syringomyelia and it surgical
correction. ClinNeurosurg 1959:6:131-140
8.
Oldfield EH,Muraszko K,Shawker TH, et al. Pathophysiology ofsy-
ringomyelia associated with Chiari I malformation of the cerebellar
tonsils:
implications
of diagnosis
and treatment.
J Neurosurg
1994:80:3-15
9.
Taylor
AR. Proceedings:
Another
theory
of
the
aetiology
of the syringomyelic cavity. J Neurol Neurosurg Psychiatry 1975:
38:825

70
SyringopleuralShunting
529
10. Welch K. Shillito ). Strand
R. et al. Chiari I "malformations":
an ac-
quired disorder? ) Neurosurg
1981 :55:604-609
11. William B. On the pathogenesis
of syringomyelia:
a review. ) R Soc
Med 1980;73:798-806
12. William B. Pathogenesis
of syringomyelia
[letter].
Lancet
1972;2:
969-970
13. Vernet O. Farmer i-Po Montes)L.
Comparison
of syringopleural
and sy-
ringosubarachnoid
shunting
in the treatment
of syringomyelia
in
children.) Neurosurg
1996;84:624-628
14. Milhorat TH. Johnson
WD. Miller )L. et al. Surgical
treatment
of sy-
ringomyelia
based
on magnetic
resonance
imaging
criteria.
Neuro-
surgery 1992;31 :231-245
15.
Dyste GN. Menezes AH. Van Gilder )c. Symptomatic
Chiari malforma-
tions: an analysis of presentations.
management.
and long-term
out-
come.)
Neurosurg
1989;71 :159-168
16.
Williams
B.A critical appraisal
of posterior
fossa surgery
for commu-
nicating
syringomyelia.
Brain 1978;101 :223-250
17.
Wisoff )H. Epstein
F. Management
of hydromyelia.
Neurosurgery
1989;25:562-571
18.
Park)L. Gleason PL. Madsen)R. et al. Presentation
and management
of
Chiari
I malformation
in children.
Pediatr
Neurosurg
1997:26:
190-196
19.
Vassilyadi M. Farmer i-PoMontes JL.Negative-pressure
hydrocephalus.
JNeurosurg1995;83:486-490

71
I
Syringosubarachnoid Shunting
Jean-Pierre Farmer and Gilles Bertrand
.
Indications
.
Contraindications
.
Advantages
.
Disadvantages
.
SurgicalTechnique
Anesthesia and Positioning
When the treatment of syringomyelia is unsuccessful at
controlling the caliber of the syrinx, given the associated
conditions leading to the syringomyelia, shunting of the sy-
rinx is indicated. Syrinx shunting to the subarachnoid space
has been used for a long time.I-S However, it is not associ-
ated with uniform success,6-Sthe reasons for which are ex-
plored in this chapter.
.
Indications
Thegeneral indicationsfor syrinx shunting apply to this
type of shunt (see syringopleural
chapter).
.
Idiopathic, posttraumatic, postinfectious syringomyelia
.
Syringomyelia refractory to Chiari decompression or to
an initial untethering surgery
.
Subarachnoid space is patent and the syrinx is segmen-
tal rather than holocord, especially if it is located at a
distance from the pleura, such as in the lumbar (Fig.
71-1) (in the case of a syrinx associated with tethering)
or cervical regions
. A patent subarachnoid space and a syrinx of limited
length (two or three segments) are usually favorable
conditions with respect to long-term syrinx control.
.
Contraindications
.
Numerous subarachnoid adhesions (e.g., postinfectious
syringomyelia or a syrinx in the context of myelodyspla-
sia), especially when the cavity is either holocord or ex-
tensive cervicothoracic or thoracolumbar
.
For the same degree of spinal cord-related
morbidity,
shunting to the pleura or peritoneum
increases the
chances of success of the surgery tremendously.
530
Incision and Musculocutaneous
Flap
Laminotomy
Intraoperative
Ultrasound
Catheter Preparation
Approaching the Syrinx
Closure
.
Postoperative Care
.
Advantages
. The operation is limited to one surgical site.
.
Shorter surgical time
.
Lesspostoperative pain
.
The syrinx will not be exposed to untoward negative
pressures or to any siphoning effect of a syringopleural
or a syringoperitoneal shunt, respectively.
.
Lessrisk ofcatheter dislodgment (Fig.71-2) thanwith
long catheters directed toward rather mobile body seg-
ments such as the posterolateral
chest wall and to a
lesser degree, the abdominal wall
.
Lowerrisk of infection perhaps because there is no extra
central nervous system (CNS)course for this catheter
.
Low risk of interference
with a coexisting ventricu-
loperitoneal (VP)shunt
.
Disadvantages
.
Rather passive system whereby the intracavity pressures
are expected to equilibrate with the subarachnoid pres-
sures at the time of Valsava's maneuvers, which, partic-
ularly for longer cavities and in situations where the
subarachnoid space is semicompetent,
may demand a
lot of a short tube placed in one particular site alongan
extensive holocord cavity
.
Through either negative pressure (pleural shunt) or si-
phoning (peritoneal shunt), gradients are higher in the
other two shunt types, which makes them more active
and more efficient at controlling the volume of large
cavities and maintaining it small.
. Apassive system that is less "active" than others
.
Better efficiency at controlling the volume of large cavities

71
Syringosubarachnoid Shunting
531
Figure 71-1
Pre- and postoperative mag-
netic resonance imaging of a patient having
undergone syringosubarachnoidshuntingfor
a segmental lumbar syrinxrelated to tether-
ing;the subarachnoid space appeared patent
at surgery.
.
SurgicalTechnique
Anesthesia and Positioning
General anesthesia is used and a single-lumen tube is usu-
ally all that is required. The patient is positioned in a similar
fashion to the syringopleural positioning. In fact, it may be
wise to include in the skin preparation a potential pleural
entry site in case the subarachnoid space is found to be in-
adequate if the planned surgery is near the pleura along the
spinal axis (Le.,thoracic).
Incision and Musculocutaneous Flap
The spinal incision considerations
are identical here to
those of the syringopleural placement technique (see Chap-
ter 70).
Laminotomy
The approach is described
in Chapter 70. A unilateral
laminectomy represents an alternative technique of expo-
sure, which may be particularly attractive in the case of a
short syrinx with competent subarachnoid space such as
those best treated by the syringosubarachnoid technique.
Intraoperative
Ultrasound
This technique is described in Chapter 70. Modern small
probes can provide adequate estimates of the syrinx charac-
teristics even through a hemilaminectomy exposure.
Catheter Preparation
Figure71-2
Spine roentgenogam showing cervical syringosub-
arachnoidshunt that has migrated to the cauda equina in a patient
withacoexistingventroperitonealshunt.
Several catheter types can be used to cannulate the syrinx.
We prefer to use a reduced-tip cardiac catheter because its
diameter is quite narrow, thereby limiting the length of the

532
Thoracic and Thoracolumbar Spine: Posterior Approach
necessary myelotomy.These catheters are designed to flow
toward the reduced tip portion: therefore it is important to
remove the slit valves at the reduced tip pole to allow free
flow.Additionally, it is good practice to add separate holes,
with either a small microscissor or a very small rongeur to
try to maintain flow within these tubes. The extra holes
made can be equally spaced along the subarachnoid
catheter and should be made in a spiral fashion along the
catheter to allow a better chance of maintaining patency.
The length of the catheter will depend on how well it can be
anchored in the subarachnoid space without causing undue
pressure on the dorsal cord and roots.
Approaching the Syrinx
Once the appropriate length of the segment of the tube
with extra holes has been determined, the actual catheter
introduction is very similar to that of the syringopleural
shunt. After opening the arachnoid and reflecting it along
the dura with surgical clips, the most appropriate myelo-
tomy site is chosen (see Chapter 70). Using microscope
guidance, the myelotomy is done with a no. 11 scalpel and
widened with the tips of a bipolar forceps. The catheter is
then introduced until all extra holes are buried in the syrinx
cavity. It is sutured to the pia with 6-0 Vicryl passed
through the wall of the catheter with a cutting needle. This
is important to limit the risk of catheter migration. At this
point, it is good practice to gently aspirate the syrinx using
a blunt needle and observe a reduction in the cord caliber to
confirm good placement.
Securing
the
catheter
represents
a challenge.
The
catheter can break or pull out as the suture is being placed,
A
B
If
rf -DentiCUlate
\ \
ligament
its lumen can be partly occluded by the suture, or a small
pial vessel can be avulsed. An alternate way of securing
subarachnoid
catheters
is the "X" catheter
placement
(Fig. 71-3). This requires a slightly larger myelotomybe-
cause two pieces of small-bore shunt catheters in which
extra
holes
are placed
are
introduced
into the sy-
ringomyelic cavity. One is inserted upward, the other isin-
serted downward. At the site of exit, they are simplytied
together with a silk ligature that is snug enough to slightly
constrict
them but not so tight as to obstruct them.
Attached as they are by the middle, they form a veryflat
Xand therefore cannot move up or down out of the cord.
They can follow the cord movements without tetheringit.
This offers the additional advantage of providing twosepa-
rate drainage pathways from the syrinx.
The distal ends of the catheters, in which extra holescan
also be made, are then slid with the least possible tension
ventrolaterally, preferably in front of the dentate ligament
where they can be anchored with a 4-0 Vicryl suture
passed around the tube and then through the inner leaflet
of the dura. Care must be taken to prevent undue pressure
on the dorsal cord or the roots to avoid irritative sympto-
matology. The dura is then closed with a continuous 4-0
PDSsuture, taking care to incorporate the arachnoid and
then removing all the surgical clips to reduce interference
with postoperative imaging. Reconstituting a patent sub-
arachnoid space as described in Chapter 70 is doublyim-
portant with a subarachnoid shunt. Not only will thisre-
duce the risk of tethering as in other shunt types, but,in
this case, the recipient area is the subarachnoid space.ln-
adequately closing it may increase the risk of treatment
failure.
Arachnoid
Dura
Figure
71-3
(A)
Operative
photo and
(B) diagrammatic
side illustration of 'X.
catheter placement technique. Notethe root
entry zone access to the translucent syrinx
in (A) and distal placement of the catheter
ventral to the dentate ligament on the side-
view diagram.

71
SyringosubarachnoidShunting
533
Closure
.
PostoperativeCare
Thewound closure is similar to that described in Chapter
70.Thedural closure tends to be more "watertight" given
thatno catheters extrude through it. Nevertheless, a fibrin
glueis applied prior to reapproximating the laminotomy
flap.The muscle, fascial. subcutaneous, and skin closures
aredescribedin Chapter 70.
References
1. Hoffman HJ.NeillJ. Crone KR.et al. Hydrosyringomyelia
and its man-
agement in childhood.
Neurosurgery
1987;21 :347-351
2. Tator CH. Briceno C. Treatment
of syringomyelia
with a syringosub-
arachnoid shunt. Can J Neurol Sci 1988; 15:48-57
3. Tator CH. Meguro
K. Rowed DW. Favorable
results
with syringosub-
arachnoid
shunts
for
treatment
of syringomyelia.
J Neurosurg
1982;56:517-523
4. Vaquero J. Martinez R. Salazar J. et al. Syringosubarachnoid
shunt for treatment
of syringomyelia.
Acta Neurochir
(Wien)
1987:84:105-109
In the
recovery room, posterior
column
and
motor
functions are ascertained. A standard spinal x-ray of the
appropriate level will serve as a baseline for catheter posi-
tion. A control magnetic resonance imaging examination
will be organized.
5.
Wisoff JH. Epstein
F. Management
of hydromyelia.
Neurosurgery
1989;25:562-571
6.
Vernet
O. Farmer J-p, Montes
JL. Comparison
of syringopleural
and
syringosubarachnoid
shunting
in the treatment
of syringomyelia
in
chiidren.J
Neurosurg
1996;84:624-628
7.
Batzdorf U. Klekamp J, Johnson
JP. A critical appraisal of syrinx cavity
shunting
procedures.J
Neurosurg
1998;89:382-388
8.
Takayasu M, Shibuya M, Kouketsu N. Suzuki Y.Rapid enlargement
of a
syringomyelia
cavity
following
syringo-subarachnoid
shunt:
case
report. Surg NeuroI1996;45:366-369

72
Syringoperitoneal Shunting
Jean-Pierre Farmer and Gilles Bertrand
.
Indications
.
Contraindications
.
Advantages
.
Disadvantages
.
SurgicalTechnique
Anesthesia and Positioning, Musculocutaneous
Flap,Laminotomy,andCatheterPlacement
Shunting a syrinx into the peritoneum is likely to be the
least commonly used procedure. Nevertheless, there are cir-
cumstances where this type of shunting is preferred and
there are theoretical advantages of this type of shunting
over other shunting methods.I-4 There are also clear disad-
vantages to using this technique.5.6
.
Indications
.
Patient with subarachnoid or pleural space unsuitable to
accept drainage from a syrinx
.
Presence of a long (holocord or regional) syrinx located
in the lumbar area in a patient with congenitally teth-
ered cord for various reasons (in these circumstances,
shunting from the lumbar area to the pleural area may
be as inconvenient as shunting from the lumbar area to
the peritoneal area)
.
Contraindications
.
Peritoneum is unsuitable to accept syrinx fluid (usually
in patients who have had multiple abdominal surgeries.
repeated ventriculoperitoneal shunt infections, a history
of bowel obstruction, and peritonitis)
.
Cervical or upper thoracic cavity that is segmental (long
catheter trajectory from dorsal to ventral, around the
chest wall, increases the likelihood of postoperative
catheter migration)
534
Transient Catheter Burial
Patient Repositioning
Peritoneal Exposure
.
Postoperative Care
.
Choice of Operation
.
Advantages
. If the syrinx is located low in the thoracolumbar re-
gion. a circumferential shunt tract around the abdomi-
nal wall may provide more shunt stability andavoid-
ance of tube migration than a shunt tract that follows
the thoracic wall toward the pleura where significant
degree of movement is seen in associationwithrespi-
ration, scapular movement, and upper extremityma-
neuvers.
. The pressure in the abdomen tends to be atmospheric
and not negative as it is in the pleura. There is,there-
fore, less likelihood of collapse of the syrinx cavityand
formation of a secondary syrinx above or belowthe site
of drainage.
. The peritoneum is usually able to absorb the cere-
brospinal fluid (CSF)well. There may still be enough
negative
pressure
created
by the siphoning
effect of the
tube to favor a more complete
initial collapse of the sy-
rinx. The likelihood
of the development
of a progressive
symptomatology
with changes
in spinal pressures may
be lower with this type of shunt
as with the syringo-
pleural shunt than with a syringosubarachnoid
shunt. In
other words, this shunt, like the syringopleural
shunt, is
active whereas the subarachnoid shunt is simplyapas-
sive small conduit in which flow depends on the estab-
lishment of episodic pressure gradients between the
cavity and the subarachnoid space at the time of aVal-
sava's maneuver.

72
SyringoperitonealShunting
535
.
Disadvantages
Transient Catheter
Burial
. Mayrequire two drapings if one is to do the cord place-
ment under microsurgicaltechnique in the prone position
. Requiresthe longest operative time of three procedures
discussed.The alternative is to do the operation in a lat-
eral decubitus position to drape the patient only once.
This is feasible, but renders the spine operation more
uncomfortable and, perhaps, the risks of tube misplace-
ment and spinal cord injury higher.
. Slightly higher theoretical risk of shunt infection (ap-
proaching that ofventriculoperitoneal
shunts) with this
type of apparatus. Shunt infection rates for syringosub-
arachnoid and syringopleural shunts, in our hands, are
extremely low.
. SurgicalTechnique
Anesthesia and Positioning,
Musculocutaneous
Flap,Laminotomy, and Catheter Placement
Thepatient is positioned prone with bolsters. Because this
operationis likely to be done at the lower thoracic and up-
perlumbar level, the surgical site will be lower. Again,care
mustbe taken to free the abdomen from bolster pressure.
Theactual operative exposure through the midline, the
laminotomy,and the catheter preparation and insertion will
be identical to the syringopleural shunt placement (see
Chapter70). Similarly, the catheter anchoring will be very
similarat the spinal canal level. Keypoints remain the use
oftransdural ultrasonography, the linear insertion in the
arachnoidand its reconstitution at the time of dural closure,
andthe placement of all extra holes into the syrinx so that
the shunt siphoning effect is not transmitted to the sub-
arachnoidspace. In the very caudal segments, one should
avoid,as much as possible, the conus region for the myelo-
tomy.It is much more sensitive to injury than any other re-
gionof the spinal cord because of the naturally condensed
natureof its fibers, both circumferentially and longitudi-
nally.It iswiser, at that site, to enter the cavity from above,
evenifthismayimplydirectingthe cathetercaudallyrather
thancephalad.Therationaleforthis modificationisto de-
compress the conus without risking damaging it in the
process.Ifsuch was the case, then a gentle loop of catheter
aroundthe spinous process located cephalad to the lamino-
tomymaybe necessary to avoid kinking the tube. Addition-
ally,a small laminar "exit window" may be needed at the
levelofthe most cephalad of posterior elements included in
thelaminotomy.
When the operation is done in the prone position and after
the catheter has be introduced and stabilized, it must be
tunneled in a subcutaneous pocket adjacent to the incision
on the side closest to the chosen peritoneal entry site. It is
then coiled and left subcutaneously. It is better to tie off the
distal end of the catheter with a silk suture applied to the
reflected end of the catheter to avoid syrinx drainage or
blood contamination during the repositioning. The incision
is then irrigated with antibiotic solution and closed with
fascial and cutaneous layers of 3-0 Vicryland 4-0 nylon su-
tures. The back incision is then coveredwith a Telfa/hypofix
dressing.
Patient Repositioning
The patient is then mobilized, still under general anesthesia,
into a lateral decubitus position. The dressing overthe back
incision is then removed and the skin is prepared to include
the flank and the abdominal wall, usually to the midline.A
horizontal incision is then planned paraumbilically.Theinci-
sion length is - 2.5cm.Subcutaneousfat isdissectedtothe
level of the anterior rectus sheath. The back incision is then
reopened to expose the fascia and the coiled catheter. Asub-
cutaneous passer, bent to follow a trajectory between the
two incisions, is then used tojoin the paraumbilical incision
to the back incision, and the catheter is then tunneled. The
bent passer should be used with its concave side up until the
midflank (Le.,midaxillary line) is reached and then rotated
along its axis so that the concave side now faces down to
complete the tunneling toward the abdominal incision.Care
must be taken during the maneuver to stay subcutaneously
and to avoid the retroperitoneum.
Peritoneal Exposure
The anterior rectus sheath is dissected, usually perpendicu-
lar to the skin incision. The muscle fibers are then separated
vertically without being cut to the level of the posterior rec-
tus sheath, which can be grabbed with two hemostat
clamps. It is then cut and the peritoneum exposed. The
peritoneum is also grabbed with hemostat clamps and cut
with scissors. The peritoneum is explored with a no.4 Pen-
field dissector (Fig.72-1) and the catheter is introduced to
a length of 25 cm. Apurse-string suture can be placed over
the peritoneum to secure the catheter in place.Theanterior
rectus sheath is closed and the subcutaneous tissue and
skin are reapproximated with 3-0 Vicrylsutures and 4-0
monocryl subcuticular sutures, respectively,forboth the ab-
dominal and the back incisions.