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

102
Surgical Management of Spinal Dysraphism
739
thinnessofthe newborn dura. The appearance of slight fluc-
tuance under the skin flaps during the first few postopera-
tivedays is likely due to a combination
of CSFand blood. As
longasthe skin closure holds, and there is no outward leak
of(SF, there is no risk of infection.
This small amount
of
seepageis self-limiting. A large transduralleak
causes a tense
subcutaneous accumulation that will eventually threaten the
viabilityof the suture line. When CSFactually breaks through
theskin barrier, the risk for gram-negative
infection rapidly
rises,and treatment must be promptly initiated.
Ashunt is effective in preventing
CSFleak but is not rec-
ommended after the leak has sprung, especially
if the leak
hasalready breached the skin closure. Even a low-pressure
shunt maintains
a constant
lumbar
CSF pressure
of 5 to
6cmH20,still considerably
higher than that in the subcuta-
neouspocket,which is near atmospheric. The preferential
passageofCSFis still out through the back wound and not
throughthe shunt. Ifa CSFleak persists in the presence of a
shunt,the latter becomes infected sooner or later.
The external ventricular
drain
(EVD) is a much
better
meansof decompression
after a substantial
leak has already
existed.The drainage
chamber
can be lowered
to subzero
pressure to siphon CSF away from the back wound.
With
elimination of outward
leakage, the probability
of infection
ismitigated. The skin edges can now be oversewn,
and the
infantmay have to be sedated
to minimize
the milking ac-
tionof muscles overlying the thecal sac. Many leaks can be
successfullymanaged
by such measures
without
a reopera-
tion.lfthe leak persists post-EVD the wound needs to be ex-
plored,and usually a discrete defect in the dura is found and
dealtwith. A new myocutaneous
closure is then refashioned.
. Open Myelomeningocele
with Segmental
Placode
Theterm segmental placode describes a portion of open
neuralplatebounded both caudally and rostrally by perfectly
neurulatedspinal cord (Fig.102-14). It isfound in -10 to 15%
ofallopen neural tube defects. The exact mechanism of its
genesisisunknown, but somehow it must involvea "square-
pulse"type teratogenic
insult to the process of primary neu-
rulation(Le., normal
neurulation
resumes
post facto to an
isolatedfailure of neural plate fusion, both in space and time).
Themost common site for the segmental placode seems to be
midthoracic to thoracolumbar.
It is unclear why the terato-
genicinsult in these cases, unlike in terminal placodes, does
notdisrupt secondary neurulation
and allows for normal clo-
sureofthe posteriorneuropore and formation ofthe conus.
It is important to recognize the placode as segmental
beforesurgicalclosure because the surgeon can be mentally
preparedto handle the distal end of the placode delicately.
Onereliableclinical clue is the preservation of distal lower
extremitymotor function while the open defect is located
highupinthe thoracicregion.Apreoperativemagneticres-
onanceimaging (MRI)scan should be obtained, not only to
visualizethe distal spinal cord beyond the placode but to
spototherassociatedparadysraphicmalformationssuchas
asplitcordmalformation (SCM),21-23
and a thickened filum.
It is even possible the segmental placode represents a
hemimyelomeningcele in that the other hemicord of the
Figure 102-14
Open myelomeningocele with segmental neural
placode. The placode is "suspended" between the fullyneurulated
proximalcord (PC)and equallywell-neurulateddistalcord (dc).
Placodeisbeingsutured rolled-up.
SCMis fully neurulated and uninvolved in the immediate
configuration of the open neural tube defect itself.21,22
The technique of closure of the segmental placode is the
same as for the terminal one. Everybit of neural tissue must
be preserved during the trimming of the extraneural mem-
brane, and every effort should be made to reconstruct the
tube (Fig. 102-14). The critical decision is whether to deal
with the other associated malformation at the same time or
at a later date. I recommend the latter since one wants to
inflict as little stress to the newborn infant as possible and
the immediate goals of infection prevention and neural con-
servation have been met by the mere closure of the open
sac. The definitive procedure of "complete" untethering
usually involves more extensive bone and soft tissue dissec-
tion, and should be left till 2 to 3 months later when the in-
fant can better withstand a longer anesthesia and larger
blood loss, when hydrocephalus is no longer an issue, and
after thorough neuroimaging studies have been obtained.
. OpenMyelomeningocele
and Kyphectomy
Aprominent kyphus is almost exclusively found with large,
high myelomeningoceles (midthoracic or higher) when the
neurological deficits are profound and at a high level. Pre-
sumably, the lackof lumbosacral paraspinous muscle action
allows overpull by the thoracic cord-innervated anterior ab-
dominal and intercostal muscles, which causes dorsal buck-
ling of the thoracolumbar spine, and secondary wedging of
the vertebral bodies at the apex of the kyphosis (Fig.
102-15). A sharp and prominent kyphus exerts enormous
tension on the closure skin flaps and compromises their vas-
cularity (Fig. 102-16). Resection of a bad kyphus not only
rids this perpendicular tension but also in effect shortens
the spine and helps in relaxing the surrounding soft tissues.
Fortunately, the necessity of kyphectomy seldom arises in
the newborn. Kyphectomyshould only be attempted if there
is no other way to achieve adequate soft tissue closure. Oth-
erwise, the spinal deformity, which will worsen with

740
Lumbar and Lumbosacral Spine: Posterior Approach
.....
Figure 102-15
Thoracolumbar kyphosis.Lateralradiograph show-
ingthree vertebralbodiesare includedinthe kyphus.
growth. should properly be dealt with using back-and-front
instrumentation
after age 5 or 6 years. However. when
kyphectomy is unavoidable at the time of sac closure. it
should be approached with painstaking regard to details be-
cause the procedure is fraught with potential mishaps.
Before kyphectomy. the thin. nonfunctional placode is re-
sected (Fig. 102-17) and the dural tube is sewn up as a blind
Figure 102-16
Thoracolumbar kyphosis. Thin and spread-out neural
placode (NP) is draped over the hump of the kyphus. There isnoreal
cyst or sac to the lesion.
B
D
Figure 102-17
Open myelomeningocele with kyphus. (A) After removal of surrounding leptomeningeal
membrane. the thin "pancake" placodeis
detached
distally and held by forceps. (8) Upward view shows the rostral normal cord and the cord-placode
transition to advantage. (C)Afterall
nerve roots have been cut, the placode is flipped downside up to show the ventral dura extending over the great kyphotic hump. (D) Resectionof
the pancake placode from normal cord. K.kyphus; p, placode; nc. normal cord; white arrows point to cord-placode
transition; D.ventral dura;dO,
dorsaldura.

....
102
SurgicalManagement of SpinalDysraphism
741
Figure102-18
Open myelomeningocele with kyphus. Pancake
placodehas been resected.
Dorsal dura
(dO) and ventral
dura
(D)closed by sutures (arrows) to form a blind stump.
K, kyphus.
stumprostralto the designatedupper cut of the kyphectomy
(Fig.102-18).Thevertebral bodies intended for resection are
nowclearedof their surrounding musculotendenous attach-
mentwith careful subperiosteal
dissection
with
the
monopolarcautery. Considerable
bleeding
from
the
epiduralveins may be expected because the thin walls
oftheseveinsareadherent to the relatively unyielding pos-
teriorlongitudinal ligament and dura, which prevent the
veinsfrom collapsing with
the
bipolar
cautery.
The
monopolarcautery dissection needle must stay close to
bone.particularlywhile separating the ventral muscles off
thebodies.Theinferior vena cava, aorta, iliac arteries, and
kidneysareall retroperitoneal structures that could get in-
juredbythe heatof the cautery or by injudicious actions of
theperiostealelevator.
Theapexof the kyphus is resected through the interver-
tebraldiskswith the monopolar cautery. The extent of re-
sectionmust take into account the feasibility
of apposing
theremainingendsof the spine to fill the gap.The two ends
ofthestumpare then cleared of cartilaginous end plates,
andbroughttogether using two parallel wire loops forced
throughthe bony part of the vertebral bodies with sharp
cuttingneedles(Fig. 102-19). A certain amount of down-
wardpressuremust be exerted on the bodies during the ap-
positionandtwisting of the wires.
Of14casesof early kyphectomy the author has done, 10
resultedin fusion.Six ofthe 10 fusion constructs remained
inacceptablealignment with < 25 degree angulation. Four
hadshownslippagebefore solid fusion had taken place, and
endedin angulation from 26 to 43 degrees. In eight of the
10patients,the spinal deformity worsened with growth in
spiteof fusion of the original construct, and all eight re-
quiredinstrumentation and refusion from 6 years onward.
Onlytwochildrendid not require further surgical treatment
forspinaldeformity.
Fourof the 14casesof early kyphectomy had disassem-
blingof the body-body construct. During twisting
of the
wireloops,the long axis of the infant's
body is being
forciblyshortened.Becauseof persistent muscle pull, the
cutendsof the kyphus still stubbornly
point backward
Figure 102-19
Open myelomeningocele with kyphus. After kyphec-
to my, the remaining vertebral bodies (B)are apposed
and sutured by
wire loops (large arrows) forced through the bodies by sharp needles.
Small arrow points to blind dural stump.
away from the longaxisof the spine.The fusion surfaces
and the wire loops are thus subjected to tremendous dorsal
and distracting stresses. Further strained by wiggling move-
ments of the infant's trunk in the postoperative period,
these wires may pull through the soft bones of the newborn
vertebral bodies. Tominimize the chances of disassembly,
the wires must not pass though any cartilaginous part of
the body or the intervertebral disk. The infant is immedi-
ately immobilized in a fitted thermoplastic body brace for a
minimum of 3 months and up to 2 years. Nonunion is a se-
rious problem because discarding one or two crumbled and
defunct vertebral bodies in preparation for a new fusion es-
sentially means widening the gap between the new fusion
surfaces and an even greater stress for the new construct.6
. Spinal CordLipomas
Anatomyand Classification
Spinal cord lipomas are classified into three types: dorsal,
transitional,
and terminal.24 Both the dorsal and transitional
lipomas insert directly into and blend with the substance of
the spinal cord; their extramedullary part forms a fibroadi-
pose
stalk that
fuses
intimately
with
the
subcutaneous
adipose
layer through
a dorsal midline
defect
in the dura,
lumbodorsal
fascia, and neural arches.
In dorsal lipomas, the fibrofatty stalk inserts
into the dor-
sal surface of the cord in one isolated, segmental region
only; the cord caudal to the lipoma
is completely
normal
and covered by normal dura.25
In transitional lipomas, the rostral portion of the fibrofatty
stalk inserts on the dorsal surface of the cord as in the dorsal
type,but the caudalportionofthe fatty stalkcontinuesdis-
tally to blend with the conus all the way to its junction with
the filum. There is, therefore, no normal cord caudal to the
transitional lipoma, and the entire distal thecal sac is incor-
porated into this stalk, with no sparing of the dural sac.25
Terminal lipomas, on the other hand, insert into the cau-
dalextremityofthe conuswithoutblendingwith the spinal

742
lumbar and lumbosacral Spine: Posterior Approach
cord or its root entry zones. All the sacral roots unmistak-
ablyleavethe conus rostral to the lipoma. and in most cases
the conus itself looks normal. The dural sac and the dorsal
myofascialcoverings are intact. The lipoma either replaces
the filum entirely or is separated from the conus tip by a
short. thickened filum.
.
Embryogenesis
It should be clear from the anatomical descriptions that dor-
sal and transitional lipomas belong in one group and share
many structural similarities. The involvement of the dorsal
spinal cord and dural tube implies that both types result
from faulty primary neurulation. In the case of the transi-
tional lipoma, inclusion of the distal conus in the fatty
mass suggests that secondary neurulation is also affected,
perhaps as a subsidiary target. Terminal lipomas. in contrast,
are a distinct entity from the other two types, with a
fully neurulated lumbosacral spinal cord and intact dural
CE
"
Neural
Plate
A
(Neuroectoderml
Healed
Cutaneous
Ectoderm
DR
tube, implying a different pathogenesis
of faulty secondary
neurulation.
Dorsal and Transitional lipomas
In primary neurulation,
the cutaneous ectoderm normallyre-
mains attached to the neuroectoderm until completefusion
of the neural folds has taken place (Fig. 102-20A). Thetwo
ectoderms then separate in a critically timed event called
dysjunction. The medially migrating mesenchyme ventrolat-
eral to the neural folds therefore can never gaincontactwith
the dorsal (ependymal)
surface ofthe neural plate.23.26
A prevalent
embryogenetic
theory
for both dorsal and
transitional
lipomas
suggests
that
the error
lies in the
premature
dysfunction
between
the cutaneous
and neural
ectoderms27-29(Le..the separation of one from the otheroc-
curs beforethe complete fusion ofthe neural folds).Thisal-
lows the paraxial mesenchyme. being constantly pushed
dorsomedially by the enlarging somitic mesoderm, toroll
over the still gaping neural folds and gain contact withthe
dorsal (ependymal) neuroectoderm (Fig.102-208). Further
Me
B
"Fusion
Line" of
:~~
~fai~::a~~~~id
DREZ
D
DR
D
P-A
C
"
~'
~
-'Distorted
Spinal
Cord
D
Figure 102-20
Embryogenesis of dorsal and transitional
lipomas. (A) Flexion of the neural folds toward the midline. Mesenchymal cellsareex.
cluded from the neural groove by the continuous
ectodermal
layer. (8) Premature
separation
(dysjunction)
of cutaneous
and neural ectoderms,
Mesenchymalcellsbegin invadingthe closing neuralfoldsand enter the central canalof the neuraltube. (C)Mesenchymeinsidethe centralcanal
is induced to form fat (intramedullary lipoma), which is continuous with the subcutaneous
adipose layer through a fibrofatty stalk. Cutaneousec-
toderm heals overthe subcutaneous lipoma to form wholesome skin. (D) Extramedullary mesenchymes are induced to form meninges,which
surround
the cord, except where the lipomatous
stalk fuses with the cord dorsally (the "fusion line"). Dorsal nerve roots issue from the spinal
cord just lateral to the fusion line joining cord, lipoma. and leptomeninges.
CE, cutaneous
ectoderm;
D, dura; DR, dorsal root; DREZ,dorsal root
entry zone; Il, intramedullary
lipoma; IF, lumbodorsal
fascia; M, muscles; ME.mesenchyme;
NC, neural crest cells; P-A, pia-arachnoid; SL,subcu.
taneous lipoma.

...
102
SurgicalManagement of SpinalDysraphism
743
closureofthe neural folds is henceforth permanently pre-
vented,anda segmental dorsal myeloschisis is created.
Experimental studies show that mesenchymal
derivatives
around the neural
tube form according
to the inductive
properties of the adjacent
neuroectoderm.8.3o
The "en-
trapped"intramedullary
mesenchyme
is being induced
by
thedorsal (ependymal)
neuroectoderm
to form fat, smooth
andstriated muscles, and collagen (Fig. 102-20C).
The ex-
tramedullary mesenchyme,
in contrast,
is induced
by the
ventralsurface of the neural tube to form meninges
(as in
thenurmal situation),
but no dura can now form over the
dorsalopened portion of the neural tube. The dural defect,
therefore,surrounds the junction
between
neural tissue and
intramedullary lipoma. Through
this dural defect, the in-
tramedullary fat links up with the extramedullary,
extra-
canalicularadipose layer to complete
a fibrofatty
stalk by
whichthe cord is tethered to the subcutaneous tissues. In
likemanner,dorsal deficiencies in the overlying myofascial
layers(from myotomal mesoderm)
and neural arches (from
scleromesoderm) also neatly surround
the lipomatous
stalk
(Fig.102-20D).
Becausethe dorsal root ganglions
develop
from neural
crestcellsat the outer surface of the neural fold lateral to its
prospective fusion site, the dorsal
nerve
roots also grow
outwardventrolateral
to, and never traverse,
the lipoma-
tousstalk.The dorsal root entry zone (DREZ)must corre-
spondinglybe very near, but always
lateral
to, the exact
junctionalinebetween lipoma and spinal cord-the "fusion
line"(Fig.102-20D).23.25
Thediscrete circumferential
fusion line of a dorsal
lipomasuggeststhat the dorsallipomais a productofpure
primaryneurulation failure and that the faulty primary
neuraltube closure occurs as a "square pulse" event; nor-
malclosuretakes place "business-as-usual"
immediately
followingthe abnormal event to result in a normal spinal
cordcaudalto the dorsal lipoma. It is interesting to note
thatdorsal lipomas are found in < 10%of all spinal cord
lipomas,an incidence which roughly parallels that of the
raresegmentalmyelomeningoceles,in which the "sus-
pended"segmentally nonneurulated placode may be con-
sideredan extreme form of segmental primary neurula-
tionfailure.
Intransitional lipomas, the myeloschisis involves much
morethanan isolatedsegmentofthe primaryneuraltube,
andtheembryogenetic event probably does not occur in a
"square-pulse"fashion. Even though its rostral part resem-
blesthe dorsal lipoma, its total involvement of the caudal
spinal cord indicates that not only is the rest of primary
neurulation disturbed by the mesodermal invasion but sec-
ondary neurulation is also profoundly affected. This ex-
plains why in many transitional lipomas, the filum is incor-
porated in the distal fat. Also,whereas the rostral fat in a
transitional lipoma is always dorsal and neatly reflects pre-
mature dysjunction, the distal fat sometimes involves both
the dorsal and ventral aspects of the conus, a situation
compatible with abnormal mesenchymal inclusion during
the much less orderly events of secondary neurulation.23
Terminal Lipoma
Terminal lipomas result from abnormal secondary rather
than primary neurulation, as evidenced by the unexcepted
rule that the lumbar and upper sacral cord segments,
products of primary neurulation, are never affected in a
terminal lipoma. Furthermore, dorsal myeloschisis and
duroschisis,
both hallmarks
of failed (primary) neural
fold fusion, are never seen. Lastly,the terminal lipoma ei-
ther replaces or forms part of a thickened filum. which
temporally places the pathogenetic process at secondary
neurulation.
Secondary neurulation comprises of three distinct stages:
(1) the condensation
of caudal eminence cells into the
medullary cord; (2) canalization of the medullary cord to
form the secondary neural canal by formation and coales-
cence of vacuoles; and (3) retrogressive differentiation of
the terminal (coccygeal) medullary cord to become the
filum terminalis (Fig. 102-21). During the normal events of
secondary neurulation, mesenchymal derivation is rarely
found in large measures within the normal conus. The fact
that the distal conus remains fat-free in cases of terminal
lipoma suggests that the pathological mesenchymal deriva-
tion did not occur during condensation.
Conversely, the
abnormal filum and terminal lipoma often contains more
(disorganized) spinal cord elements and ependymal tubules
than in a normal filum,31.32as if the retrogressive processes
in these situations have been incomplete or "ineffectual."
Also,excessive amounts of nonadipose mesenchymal deriv-
atives, such as cartilage, bone, and fibrous septa, are found
within many terminallipomas.23 Thus, the evidence con-
cerning embryogenesis of these lipomas points to an abnor-
mal retrogressive differentiation of the secondary neural
cord, brought about by an aberrant accumulation of mes-
enchymal precursor cells from the pluripotential caudal cell
mass.23

..
744
Lumbarand LumbosacralSpine:PosteriorApproach
N
CE
CM
H
--
A
E
c
E
.
OperativeTreatment
Electrophysiological
Monitoring
Realtime somatosensory evoked potential (SSEP)monitor-
ing is used routinely with surgical resection of spinal cord
lipomas. Sensory conduction through the lower lumbar
and Sl segment is monitored via surface-stimulating
electrodes overlying the common perioneal nerve and pos-
terior tibial nerve. Pudendal nerve electrodes placed over
the dorsum of the penis or clitoral-labial skin is utilized
for the lower sacral cord segments. In patients with a
complete L2sensory level, the lateral femoral cutaneous
nerve (Ll dermatome)
can be accessed through needle
Co
N
CE
CM
A
NT
NT,
us
Figure 102-21
Secondary
neurulation.
(A) At stage 12, the primitive
streak israpidlyregressingand isgraduallyreplacedbyanemergingmass
of pluripotential cells, the caudal eminence (caudal cell mass) situatedbe.
tween Hensen's node and the cloacal membrane anlage.(8) Withen.
largement
of the caudal eminence
and associated ventral foldingofthe
embryonic
tail, the cloacal membrane
is pushed ventrally. (C) Ventral
folding of the yolk sac encloses the hindgut, which later dilates to form
the cloaca. Condensation
of the prospective
neural cells from the caudal
eminence
forms the medullary
cord, the future secondary neuraltube
(first stage
of secondary
neurulation).
(D) Vacuoles appear in the
medullary cord, which coalesce to form the secondary neural canal(canal.
ization, second stage of secondary
neurulation).
At the same time,the
urorectal
septum
grows toward the cloacal membrane
(short arrow).
(E)Retrogressivedifferentiationof the distal medullarycord (thirdstage
of secondary neurulation) converts this part into the filum terminalis.The
proximal part remains to form the conus. Long arrows in C, D,and Ede.
note boundary between primary and secondary neurulation. A,allantois;
C, cloaca; CE, caudal eminence; CM, cloacal membrane; CO,conus;E,en.
doderm; F,filum terminalis; H, hindgut; MD, mesonephric duct; N,noto-
chord; NE, neuroectoderm;
NT" primary neural tube; NTb secondary
neural tube; P,primitive streak; U, urethra; US,urorectal septum.
electrodes placed just medial to the anterior superioriliac
spine.33
Forintraoperative identification of the lowersacralmotor
roots, an external anal sphincter balloon pressure monitor
inserted just deep to the anal verge will displaycontraction
of the sphincter to direct monopolar stimulation of the
roots in question.34Alternatively,electromyographicrecord-
ing needles inserted into the external anal sphinctermaybe
used to pickup motor action potentials.33
Dorsal Lipomas
The goal of surgery for any spinal cord lipoma is to relieve
the tethering
effect of the fibrofatty
stalk on the cord. Itis

102
SurgicalManagementof SpinalDysraphism
745
~-
~.
-
~~,
---
:
~
A
B
Figure102-22
Dorsal lipoma. (A) Drawing shows extradural component
of the lipoma going through a discrete midline dural defect that can be
circumferentiallyoutlined. Dotted line indicates place of dural opening. (8) Intraoperative
picture after laminectomy.
Dural defect outlined byar-
rowheads.EL,extradural lipoma: D, dura.
thereforeimportant to locate the exact location of thefusion
linewherethe fat,spinal cord, and leptomeninges meet.
Inthe dorsal lipoma, the fusion line can be traced circum-
ferentially about
the
fatty
stalk-spinal
cord
interphase,
sincethe cord caudal to the stalk is normal. Because at this
sitethe embryonic neural
folds never coapted
in the mid-
line,the DREZis displaced just lateral to this line. The DREZ
andthe entries of the dorsal
nerve roots form a neat oval
aroundthe fusion line. The dorsal dural defect is a complete
circular or elliptical
hole
around
the
fatty
stalk
(Fig.
102-22). In some dorsal
lipomas,
the margin of the dural
defectisadherent to the fusion line. In others, the dural de-
fectis detached from the fusion line, a considerable in-
traduralportion of the fatty stalk, smooth,
pia covered, and
paleryellow than the extradural fat, traverses free sub-
arachnoidspace obliquely for a fair distance
before attach-
ingto the cord rostrally. This reflects continued
upward as-
censionof the neural tube in relation to the dural tube after
the mesenchymal
invasion
of the cord. The fatty stalk is
draggedupward by the cord for a short distance.
Atsurgery, the plump subcutaneous
fat pad (Fig. 102-23)
issharply dissected and "reduced"
around the lumbodorsal
fascialdefect. The deep surface of this fat pad is the "outer
end"of the lipomatous
stalk, which plunges through
a dis-
cretedefect in the midline
lumbodorsal
fascia. The fascial
rentisenlarged rostrally and caudally, to expose the under-
lyingspinous process and laminae. The discrete
fatty stalk
cannow be followed though a neural arch defect. The lami-
naeone level above and one level below are removed.
The dura is opened
in the midline
rostral
and caudal to
the stalk, and then around
the stalk on each side. This re-
veals two crucial features,
the fusion
line between
fatty
stalkand cord, and its DREZimmediately
lateral to the fu-
sionline.The cord caudal to the stalk is never involved with
fat(Fig.102-24). The releasing cut is made along the fusion
linejust medial to the DREZto avoid the dorsal roots, flush
withthe surface of the cord without
attempting
to "dig out"
intramedullary
fat (Fig. 102-25).
After complete
detach-
ment of the fatty stalk from the cord, a thickened
filum is
alwayssought at the tip of the conus and divided if found.
Transitional Lipoma
The most rostral portion of the transitional lipoma (Fig.
102-26) resembles the dorsal lipoma in that the fusion line
is quite distinct, and the dorsal roots emerge just ventrolat-
eral to this line. The cord is, in effect, suspended from the
dorsal dura by the lipomatous stalk. Caudally,however, this
fusion line is displaced ventrally as the lipoma gradually
Figure 102-23
Large subcutaneous
lipoma overlying a dorsal lipoma.

746
lumbar and lumbosacral Spine: Posterior Approach
A
-=-1
{ \
\
B
Figure 102-24
Dorsal lipoma. (A) Drawing and (B) intraoperative
photo showing smooth intradural component
of the lipoma (pia-covered)and
palerincolor.Notediscrete circumferentialfusionline(outlined byarrowheads)between fat, pia-arachnoid,and spinalcord. Dorsalrootentryzone
(DREZ)and dorsalrootlets are lateralto fusionline.C.conus;EL,extradurallipomas;IL,intradurallipoma.
replaces more of the terminal conus toward the caudal end
of the thecal sac. The neural placode is thus reduced to a ta-
pering wedge, as when a flat beveled cut is made obliquely
across a stick from its top surface. The dorsal root entry
sites are accordingly displaced more ventrally following the
oblique fusion line; all the roots, therefore, course in the
(SF space ventral to the placode and lipoma, and no matter
how large the fat mass, the nerve roots are not enmeshed in
it (Fig.102-27). Frequently,the DREZsare more caudally lo-
cated than their corresponding ventral root exits, suggest-
ing a viscous upward sliding of ventral cord tissues against
an entrapped dorsal half of the neural tube (Fig.102-27).
The dura is opened just rostral to the upper end of the
lipomatous stalk (Fig.102-28). Thisexposes the rostral por-
tion of the transitional lipoma, which is usually well demar-
cated from the cord. The detaching cut along the fusion line
should begin here and proceed caudally, using essentially
the same technique as for a dorsal lipoma (Fig. 102-29).
Soon, however, the lipoma expands to fill the spinal canal
,~
\, ..~
,,~
.
\-.
and covers up the fusion line. In my opinion, dealingwith
the caudal part of a large transitional lipoma is the most
hazardous
operation
among
all occult dysraphic and
paradysraphiclesions,and alsois associatedwiththehigh-
est morbidity. There is variability not only in the relation-
ship of the lipoma to the spinal cord and leptomeninges
rostrocaudally but also from one side of the spinal canalto
the other. Ifthe patient's neurological level is asymmetric,
the side with the worse deficits always corresponds tothe
side on which the lipoma infiltrates the conus moreexten-
sively,where the fusion line (and rootlets) is displacedmore
ventrally, and where the dura is most deficient.
Theimportant perspectiveto keep is the unvaryingfact
that the lipoma lies dorsal to the horizontal planejoining
the fusion line from side to side. and that the only free(SF
space containing all the nerve roots lies ventral to thisplane.
As long as a parallax view of the DREZ(in (SF space)on
the one side and lipoma (dorsal to (SF) on the other sideof
the fusion line is obtained by looking in a rostral-caudal
A
'
~w
--B
Figure 102-25
Dorsal lipoma. (A) Drawingshowing resection of lipomatous stalk flushed with the cord surface just medial to fusionline.
(B)Postresectionpicture showingcut surface(C5)oflipomastump, and completelynormalconus (C)distally.

I
102
Surgical Management
of Spinal Dysraphism
747
A
_-
B
Figure102-26 MRIoftransitionallipoma.(A)Sagittalimageshowingdorsallocationofthe fat and involvementofthe distalend ofthe conus.Note
terminalsyrinx.(B)Axialview at proximal portion showing dorsal location of the fat and the ventral placode. This part is identical to a dorsal lipoma.
direction,the lipoma can be safely detached from the cord
millimeterby millimeter toward the conus tip. It is always
easiertofindthe ventral (SF space on the neurologically bet-
terside.After this fusion line is freed, the placode can then be
gentlyrotated toward this side to expose the ventral (SF
Figure102-27
Transitional
lipoma. The rostral and more dorsal por-
tion isthe only distinct
part that resembles
a dorsal lipoma.
Caudally,
thelipoma merges with general extradural
fat. The oblique
fusion line
(outlined by arrowheads)
stretches
from
a rostral-dorsal
point
to a
caudal-ventral point at the tip of the conus. The fat involves most of
thedistal conus, but a discrete filum (F) is often seen partially
buried in
fat.DREZ,dorsal root entry zone.
space and the dorsal roots on the more extensive side of the
lipoma, so that a matching cut can be made on this fusion
line. The final cut surface of the lipomatous stalk is therefore
a dorsoventral oblique plane from rostral to caudal, with a
slight tilt toward the more involved side (Fig. 102-30). A
thickened filum is frequently present on the ventral tip of
the wedge-shape neural placode,which must be cut to com-
plete the untethering.
Occasionally, one or two distal
rootlets are fibrotic and taut. After any useful function has
been ruled out by intraoperative stimulation, these atrophic
rootlets should also be cut to release the conus.
Although some surgeons claim that using the carbon
dioxide laser can eliminate much of the intramedullary fat,
the author prefers the feel of the microscissors on the fibro-
fatty septi to provide instant
tactile feedback on the
lipoma-cord interface. There is a thin, indistinct, white,
tough fibrous zone (not a real plane) that separates the yel-
low fat from the pink, soft spinal cord tissue. If the sharp
dissection stays within this layer, most of the fat can be re-
moved with safety.
Retethering is usually due to a constricting dural closure
rather than regrowth of residual lipoma. If the remaining
neural placode is thin and supple, it should be rolled upon
itself and stitched with several 8-0 nylon sutures. This con-
verts the dorsal "raw" cut surface to a narrow midline seam,
and reduces the adherent surface greatly. Alarge dural graft
(e.g., with bovine pericardium) is then sewn in to create a
capacious sac so that the now floppy terminal conus can

748
Lumbarand LumbosacralSpine:PosteriorApproach
A
-'
-~
B
Figure 102-28
Transitional lipoma. (A) Drawing and (B) intraoperative exposure showing large extradural fat component,
distinct rostralduralde-
fect, but less distinct distal planes where lipomatous septae and dura blend indistinguishably. Dotted line in (A) shows dural opening from rostralto
caudal.
I:f
I.. I
..
:1
A'
zP
~ .Jh
Figure 102-29
Transitional lipoma. (A) Drawing shows the plane of incision along the fusion line (dotted). There is always an indistinct planeof
fibrous tissue between fat and spinal cord that can be exploited during the sharp dissection. (B) Intraoperative
photo showing the same perspec'
tive, from rostral to caudal. Fusion line outlined by small arrowheads.
Dorsal root entry zone (DREZ)lies just outside of fusion line. IL,intradural
lipoma.
j
7 1
//'
A
-
.
~-
_
"B
Figure 102-30
Transitional lipoma. (A) Drawing and (B) intraoperative
photo showing oblique cut surface of the neural placode in the shape ofa
bevel. Note complete removal of fat and the intermediate plane of thin fibrous tissue.
r
!II
if
.... -

Figure102-31
Terminal lipoma. Magnetic resonanceshows inter-
veningthickfilum andlarge distal lipoma.
movefreely within (SF with changes of body position,
therebydecreasing the probability of prolonged contact be-
tweenthe placode and the dural suture line.
TerminalLipoma
Theterminal lipoma either inserts directly into the caudal
extremityof the conus or is separated from the conus by a
shortsegmentof thickened filum (Fig.102-31). When there
isnointervening filum, the junction between lipoma and
102
Surgical Management of Spinal Dysraphism
749
conus is usually readily identifiable by the yellow color of
the fat, the more sparse vasculature over the lipoma versus
the copious pial vascular network on the conus, and the fact
that the last pair of nerve roots exit the cord just before the
lipoma. When there is an intervening filum, the latter's
junction with the conus can be obscure because there is no
color difference, and the conus tip is usually tapered and
continues into the filum without a change in contour. How-
ever, the
serpiginous
cord vessels suddenly
become
straighter on the filum, and the substance of the filum itself
is seen to consist of parallel strands of gristly tissue that are
clearly nonneural.
In either situation, the dura overlyinga terminal lipoma is
intact, and its opening presents no problems because there
is no adherence between lipoma and dura (Fig. 102-32).
With the "direct insertion" type, the low sacral nerve roots
exit the conus at points distinct from the lipoma (Fig.
102-33), but in their distal course the nerve roots may be-
come adherent to the ventral surface of the lipoma, even
though they are not enmeshed in the fat.These "hitchhiker"
roots must be carefully peeled off the fat and kept out of
harm's way along most of the length of the lipomawith cot-
tonoid micropatties (Fig. 102-34). The conus-lipomajunc-
tion is first cut across transversely to release the cord before
the distal cut is made to complete the resection of the
lipoma (Fig.102-35). Hitchhiker roots are likewise carefully
peeled off from the distal type of terminal lipoma with an
intervening filum. The filum is then firmly grasped by mi-
croforceps and gently pulled up toward the conus, while the
part distal to the grasp is cauterized to coagulate an ever-
present longitudinal ventral vein. This maneuver of proxi-
mal grasping is important
because cauterizing a filum
acutely shortens it and instantaneously increases the ten-
sion on the conus by severalfold. Thus the firm grasp on the
proximal filum is not released until the cauterized part is
cut completely across. As soon as this is done, the conus is
out of danger, and its free end can be seen to pulsate loosely
in the (SF. Without this precaution, the pudendal SSEP
has been known to disappear during cauterization of the
distal filum. The rest of the lipoma can now be removed at
leisure. As with the dorsal lipoma, primary dural closure
can usually be accomplished without a graft,23
A
-
--"
;.- .
B
Figure 102-32
Terminal lipoma. (A) Drawing and (B) intraoperative
exposure, showing intact dura. Dotted
line in (A) indicates dural opening.

750
Lumbar and Lumbosacral Spine: Posterior Approach
Figure 102-33
Terminal
lipoma,
direct
insertion
type,
shows dis-
tinct junction
between conus and lipoma. All nerve roots exit rostral to
this junction.
Note copious
serpiginous
vessels on the surface of the
conus abruptly
changing to sparse straighter
vessels.
.
Outcome
Resection of lipomas and release of the tethered
spinal
cord can be accomplished with minimal morbidity. When
the outcome is analyzed with respect to the preoperative
symptoms, the best operative result is seen with pain.
Most of the sharp, dysesthetic leg and perineal pain will
significantly diminish, even though some patients may be
left with low back pain that is likely mechanical in ori-
gin.3s.36The improvement occurs within the first 3 months
after the operation, and children spontaneously
become
more active and playful. It is very unusual to encounter
chronic back complaints in children after tethered cord
release, as are sometimes seen in the adult tethered cord
patients.23
Sensorimotor deficits also respond favorablywith surgery.
Although < 20%of patients have actual normalization of
motor function postsurgery, the majority will make substan-
tial improvement.24.25.36-37
As with other forms of tethered
cord, the milder and more recent deficits have a better
Figure 102-34
Terminal lipoma, direct insertion type. Hitchhiker nerve
roots must be detached from underside of lipoma before resection.
chance for good recovery. Among the three lipoma types,the
large transitional
ones are the most likely to be associated
with increased
sensorimotor
deficits after surgery. Overall,
the worsening rate is < 2%.23
Bladder dysfunction responds favorably in-20 to 30%of
patients with spinal cord lipomas.35.37-41The subtype ofneu-
ropathic bladder with the best prognosis is the smallcapac-
ity, spastic bladder
with uninhibited
detrusor
contraction.
Atonicbladders with large residual volumes seldom improve
with surgery, and intermittent catheterization usuallyneeds
to be continued
indefinitely.
The response
of detrusor-
sphincter
dyssynergia
to surgery
is unpredictable.
It is
mandatory
that cystometry
and voiding cystourethrogram
be repeated
3 to 6 months
after surgery to determine what
other urological
procedures
such as bladder augmentation
or ureteral conduits
may be necessary
to prevent refluxand
frequent
infections.
Surgery has been known to arrest the
rapid worsening of existing scoliosis in tethered cord.How-
ever, severe scoliosis still requires surgical realignment and
fixation with instrumentation
and fusion.
A
~
..
"..
..;-' B
Figure
102-35
Terminal lipoma.
(A) Detaching
lipoma from conus at the clear transition
line. (B) Retraction
of conus from the lipoma after com-
pletion of cut. Note previously taut conus vessels now looking relaxed.

...
.
Limited Dorsal Myeloschisis
102
SurgicalManagement of SpinalDysraphism
751
Thisform of spinal dysraphism
is called transitional
because
it is neither open, with a cystic, CSF leaking, placode-
mounted sacas inthe common variety of myelomeningocele,
noris it truly occult (or closed), without
any obvious cuta-
neousstigma, as in many cases of spinal cord lipomas and
splitcordmalformation.Thebasic structure of a limited dor-
salmyeloschisis(LDM)consists of a fibroneurovascular stalk
containingneurons, glia, and nerves emanating from the dor-
salsurfaceofthe spinal cord and penetrating
though
a nar-
rowdorsaldural opening to reach the surface of the skin. The
presenceof an LDMis always indicated on the overlying skin
byoneof four manifestations: (1) a prominent dimple or
crateron the dermis, often with heaped up, thickened skin
edges(Fig.102-36); (2) a round or oval area of unusually
thinskinwithout underlying dermis, or a pearly, squamous
membrane surrounded by slightlyelevated skin,which in the
pastwascalled agenesis cutis congenta; (3) a fluid-filled,
fluctuant,skin-covered mass with or without an unobtrusive
centralcrater,which in many instances was called meningo-
cele;and (4) a fluid-filled, fluctuant mass with a skin-
coveredbasecapped by a thick, purplish, raw looking squa-
mousepithelial membrane (Fig.102-37).
Thus,LDMis transitional between open myelomeningo-
celeandthe closed dysraphic lesions in form and structure
only,andnot in embryogenesis.In truth, its embryogenesis is
probablymuch closer to the open myelomeningocele than to
lipomasandsplit cord malformations (see later discussion).
LDMsare rare lesions found in all areas of the spine, but
morecommonlyin the lumbar and thoracolumbar regions.21,22
Asisapparentbelow,LDMsarelesionsof primary neurulation
andthusdo not usually involve the true conus, which is a
productofsecondaryneurulation. In the cervicalregion,LDMs
arealmostalways of the sac type, particularly with the pur-
plishlichenized squamous epithelial cap42,43forming an im-
posingprotrusion in the back of the newborn's neck. Cervical
Figure 102-36
Skin dimple overlying a lumbar limited dorsal
myeloschisis(LDM),showing heaped up skin edges and surrounding
capillaryhemangioma.
A
B
Figure 102-37
Cervical limited dorsal myeloschisis with a fluctuant
fluid-filled protuberance
that is skin-covered at the base but capped by
a thick, purplish squamous epithelial membrane.
(A) View from back.
(B) Side view.
LDMs are associated with
the Chiari II malformation
and hy-
drocephalus
in approximately
half of the cases reported,28.42.43
whereas lumbar and thoracolumbar
LDMs seldom are.
.
Embryogenesis
An LDMprobablydiffers from the flat terminal neuralpla-
code of an open myelomeningocele
only in the degree of the
incompleteness
of neurulation.42
In LDM, most of the neuru-
lation has occurred except for the final fusion of the opposed
neural folds (hence dorsal myeloschisis).
The basic configura-
tion of the neural tube has taken shape, except for a thin slip
in the dorsal midline
(hence limited).
Here, dysjunction
(sep-
aration)
between
cutaneous
ectoderm
and neuroectoderm
never
truly
happens,
but
the
midline
gap
between
the
converging
cutaneous
ectoderm
and dorsal
scleromytomes
from opposite sides of the embryo
remains very narrow (Fig.
t02-38A).
Further development
of the full-thickness
dorsal

752
lumbarandlumbosacral Spine:PosteriorApproach
Incomplete
Fusion
. ,
A
Bridging Squamous Epithelium
Skin
:: :.
...-.
Dorsal Fascia
Dorsal Musculature
Dura Extending
Around
Neural
Tissue
Stalk
Bifid
Neural Arch
CSF
Centrum
B
Notochord Remnant
Figure102-38
Formationoflimiteddorsalmyeloschisis.(A)Incompletedorsalmidlinefusionand nondysjunctionbetween cutaneousandneural
ectoderms.Thedorsal neuraltube retains an attachment to the overlyingskin.Notethe retention of neuralcrest cellsinthe dorsaladhesiontoform
nerve roots and dorsal root ganglia in the future fibroneural stalk. (B) Growth of dorsal myofascial tissues progressively pushes the neural tube away
fromskin,but the cutaneoneural attachment remainsas the lengthening neural stalkcontaining central and peripheral neuraltissues.Notesqua.
mous epithelium crossing the gap on the skin.

102
SurgicalManagementof SpinalDysraphism
753
myofascialtissues (except for the narrow strip of midline)
progressivelysets the integument
farther
away from the
neuraltube,whichultimately retains its primarily intraspinal
location.Adorsalmedian stalk of central nervous system tis-
sue,however,remains as the original link between the nearly
closedneural tube and the stiJI slightly gaping cutaneous
ec-
toderm(Fig. 102-388).
Underneath,
normal
meninges
de-
veloparoundthe neural tube and extend around the midline
neuralstalk as a sleeve that projects to the surface. Superfi-
cially,the small dimple or pearly thin membrane
belies the
smallunclosedgap of the cutaneous ectoderm, but in some
cases,thick squamous epithelium
grows across and bridges
thisgap,even though this membrane
lacks a full-thickness
epidermisand dermis.42 As (SF forms around
the neural
tube,it also squeezes into the dorsal dural fistula around the
neuralstalkand ultimately distends the thinner, less well-
supportedsquamous epithelial portion of the gap into a
fluid-filledand mostly skin-covered sac (Fig. 102-38C). The
Basal Neural Nodule
'.
crater, dimple, and otherwise "unskinlike" cap of the dome
always belie the originaldorsal myeloschisis.
The internal structure of the sac, dorsal to the fibroneural
stalk, can be of three forms. If there is an associated hy-
dromyelia in the part of the cord bearing the dorsal
myeloschisis, (SF may distend the center of the distal
neural stalk dorsal to the myofascia into a large myelocys-
tocele within the meningocele sac42.44(Fig. 102-39).
If
there is no hydromyelia, the neural stalk remains solid and
narrow and fans out on the dome of the sac (Fig. 102-40).
Or the (SF pressure within the sac may compress the
neural stalk ventrally into a series of basal neural nodules
lining the bottom of the sac (Fig. 102-41). In all variations
of the intrasaccular neural component, the dorsal spinal
cord underneath the sac is tethered to the myofascial tissue
by way of the fibroneural stalk and its meningeal invest-
ment. Neurological deficits develop because of this tether-
ing effect and vary according to the location of the LDM.

754
Lumbar and Lumbosacral Spine: Posterior Approach
~~
~=-
~'~
~
1l,
...~~~,
"I
F~~~
,,'
"'1' -",:.~ ,
~
"..0. ~~:
~'."
.,
0
~
'
,. '"
, ';
P. ~
oJ
,~
t~;
.~..
"
SA
~\,
f
",.
""
..'\ .
,,,Ill , ,,'
.
'" If, .. ' ::.'.'~'
.. #;:.
""
,
fit~:
f. '.
A
\I.,.,."}
q.,.
B
Figure 102-39
Limited dorsal myeloschisis (LDM)with myelocystocele.
(A) Drawing shows the LDMsac consists of two chambers. The outer
chamber is a meningocele
continuous with the subarachnoid
space of the dural stalk and spinal cord. The inner chamber is the myelocystocele sac
continuouswith a smallhydromyelicdistention ofthe underlyingcord. Itislined byan atrophic, ependyma-lined neural membrane. D,dura:Mye,
myelocystocele; SA,subarachnoid space. (8) Computed tomographic
myelography shows the outside meningocele sac fillwith contrast, beingcon-
tinuous with the spinal subarachnoid space. The inner myelocystocele sac is not contrast filled.
Figure 102-40
Limiteddorsal myeloschisis(LDM)with narrow fi-
broneural stalk (white arrows)that fans out on the dome of the sac.
The underlyingcordistented uptowardthe baseofthe sac.
Figure 102-41
Limited dorsal myeloschisis (LDM)with basal neural
nodule (arrow) shown on magnetic resonance. Fibroneural stalk isin-
dicated by arrowhead.

. SurgicalIndications and Treatment
Giventhenonleakingnature of LDMsand the tethering ef-
fecton the spinal cord, the indication
for surgical manage-
mentisnotsomuchsoft tissue closure to guard against CSF
leakageaseliminationofthe pull on the spinal cord by the fi-
broneuralstalk. Referring back to a past era of neurosurgery,
whenalotofinfants with these large disfiguring protuber-
ancesonthebackofnecks and backs were treated by resec-
tionoftheoffensivelump and subcutaneous ligation of the
dorsalstalk merely for cosmetic effects, the author saw
manysuchcasesreturning with progressive neurological
deteriorationdue to the unaddressed tethered cord. In a
priorseries,six of nine cases of cervical LDMsso treated
hadprogressivemyelopathy requiring more definitive
surgery.42
Another very important consideration regarding treat-
mentisthe frequent association of other tethering lesions
withLDMs.Forexample, three out of nine patients with
cervicalmyelomeningocele(LDMs)in our series42also had a
type/Isplitcordmalformation21adjacent to the fibroneural
stalk,exertingasecond site of cord tethering by way of the
attachmentofthestifffibrousseptum to the hemicords.A
thickenedfilumisalso commonly found with thoracolum-
barandlumbar LDMs,and in three of nine patients with
cervicalLDMspreviouslyreported. In addition, -50% of cer-
vicalLDMsare known to have a Chiari IImalformation42.43
and60%havehydrocephalus, all relevant statistics in the
comprehensive
management of these infants.
Thus,Irecommend the following surgical principles re-
gardingLDMs:(1)obtain preoperative neural imaging stud-
ies(MRI;myelographywith computed tomography) of the
entireneuraxisto identify all associated abnormalities; (2)
102
Surgical Management of Spinal Dysraphism
755
perform adequate laminectomy to visualize not only the at-
tachment of the fibroneural stalk of the LDMto the "parent"
spinal cord, but also the associated lesions; (3) perform re-
section of the fibroneural stalk flush with the dorsal surface
of the cord; (4) explore for hidden fibrous septum of split
cord malformation or lipomas; (5) perform resection of the
thickened filum; and (6) treat the cranial lesions when
indicated.
Theoperationfor LDMsisquitestraightforward;it isthe
same whether the internal structure of the LDMsac con-
tains a myelocystocele, a basal neural nodule, or a slender,
simple fibroneural band. The skin incision incorporates an
elliptical split around the base ofthe sac and affords enough
rostral and caudal exposure for at least one set of intact
laminae both above and below the dural-neural stalk. The
often thick subcutaneous adipose tissues are carefullygone
through to reveal the funnel of dura at the base of the sac,
narrowing deep into the discrete stalk that penetrates
through a defect in the myofascial layer (Fig. 102-42A).
Laminectomy is done to display the normal dural tube
rostral and caudal to this dural stalk, which is thus seen in
continuity with the dorsal dural outpouching. The dura is
opened in the midline, the cord is explored, and the dorsal
dural outgrowth is laid open to show the fibroneural stalk
and the almost always discrete attachment
of the stalk
with the spinal cord (Fig. 102-428). The stalk is simply cut
flush with the surface of the cord (Fig. 102-42C-F). Anyas-
sociated tethering lesions should be dealt with. A remote
thickened filum may require a separate laminectomy. The
dura is closed primarily. The superficial sessile sac, now
detached, can be resected en masse. The steps of resection
ofa lumbarLDMwith a simplefibroneuralbandare shown
in Fig. 102-43.
A
~
~..;.
...
~
-- .,.
B
Figure102-42
Resection of a cervical sac type limited dorsal myeloschisis with basal neural nodules. (A) Subcutaneous
exposure of the dural fis-
tulaasitpenetrates the midline defect in the ligamentum
nuchae. Note elliptical skin incision for excising the base of the skin-covered sac. (8) In-
traduralexposure showing
the dorsal
fibroneural
stalk (displayed
by the microhook)
arising
from the dorsal
cord surface
(arrows)
and entering
the
duralfistula (DF), opened longitudinally. The neural stalk ends in the basal neural nodule (arrowheads)
at the base of the sac, still maintaining the
originalproximity to the skin.
..

c
756
Lumbar and Lumbosacral Spine: Posterior Approach
D
F
Figure102-42 (Continued) (C)The base ofthe stalk iscut flushwiththe dorsalsurface ofthe cord. (D)Cutsurface ofthe stalkattachmenttothe
dorsal spinal cord, displayed by the microdissector.
(E) Basal neural nodule within the base of the sac. (F) Histopathological
features of the basal
neural nodule, consisting of large glioneuronal nubbins (GN), ganglia cells (G), and peripheral nerves (N).
A
B
Figure 102-43
Lumbar limited dorsal myeloschisis (LDM)with a simple fibroneural band. (A) The skin dimple is excised. The cutaneoneural stalkis
followed down to a defect in the lumbodorsal fascia (arrows). (8) After laminectomy above and below the fascial defect, the dural stalk istracedtoa
midline dorsal dural outgrowth from the thecal sac.

jIIII
102
Surgical Management of Spinal Dysraphism
757
c
"
I
.
I.~
.
D
Figure102-43 (Continued)
(e) After dural opening,
the intradural
portion
of the fibroneural
stalk (small arrow), consisting of glioneuronal
tissue,
nerves,and blood vessels, is seen attached
to the dorsal conus (large arrow).
(D) The complete,
resected
fibroneural
stalk showing the cuff of skin
aroundthe dimple at one end, and the spinal cord attachment
at the other end.
References
1. PangD.Surgical management of split cord
malformations.
In: Wilkins
R, Rengachary S, eds. MNS Neurosurgical Operative Atlas. Vol 3.
1993:135-149
2. PangD.Sacralagenesis and caudal spinal cord malformation. Neuro-
surgery 1993:32:755-779
3. Pang D. Caudal agenesis
and dysembryogenesis
of the caudal
spinal
cord. In: Pang D. ed. Disorders
of the
Pediatric
Spine.
New York:
Raven; 1995:277-308
4. Warkany j. Morphogenesis
of spina
bifida.
In:
McLaurin
RL, ed.
Myelomeningocele.
New York: Grune and Stratton:
1977:31
5. O'Rahilly R, Muller R. Developmental
stages in human
embryos.
in-
cluding a revision of Streeter's
"Horizons" and a survey of the
Carnegiecollection. Carnegie Institute of Washington Publication 637.
1987: 123-139
6. PangD.Surgical complications
of open spinal dysraphism.
In: Pang D,
ed.NeurosurgeryClinics of North America. Vol6:2. Philadelphia: WB
Saunders: 1995:243-257
7. SensenigEC.The early development of the meninges of the spinal
cord in human embryos.
Contrib EmbryoI1949:33:21-41
8. Kallen B. Early embryogenesis
of the central
nervous
system
with
special reference
to
closure
defects.
Dev
Med
Child
Neurol
1968:16(Suppl):44-53
9. McLane DG, Dias MS. Complications
of myelomeningocele
closure.
Pediatr Neurosurg
1991-1992;17:267-273
10. HabalMB, Vries jK. Tension-free closure of large meningomyelocele
defects. Surg NeuroI1977;8:177-180
11. Ramirez OM, Ramasastry
SS. Granick
MS, et al. A new surgical
ap-
proach to closure of large lumbosacral meningomyelocele defects.
Plast Reconstr Surg 1987:80:799-807
12. Ames MD, Schut L. Results
of treatment
of 171 consecutive
myelomeningoceles,
1963 to 1968. Pediatrics
1972:50:466-470
13. Melone DG.Treatment
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arguments
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1986;33:359-370
14. Reigel DH, McLone DG.Myelomeningocele:
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results. In: Marlin AE, ed. Concepts
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15. McLoneDG.Technique for closure of myelomeningocele. ChildsBrain
1980:6:65-73
16. McLone DG. Dias MS, Kaplan WE. Concepts
in the management
of
spina bifida.
In: Humphreys
R, ed. Concepts
in Pediatric
Neuro-
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Pang D. Split cord malformation.
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Pang D. Dias MS, Ahab-Barmada
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Pang D.Spinal cord lipomas. In: Pang D,ed. Disorders ofthe Pediatric
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Chapman PH. Congenital intraspinal lipomas: anatomic considera-
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Pang D.Tethered cord syndrome in neurosurgery. State of the Arts Re-
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McLoneDG.Naidich TP.Spinaldysraphism: experimental and clinical.
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Neurosurgery
1983;13:562-568
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Hoffman Hj, Hendrick
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Bruce DA. Schut L Spinal
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Dubowitz
V. Lorber j. Zachary
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Fukui j. Kodaira K.Waranabe
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G. Diastematomyelia:
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1975;10:87-93
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Pang
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Dias
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Cervical
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1993;33:363-373
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Steinbok
P. Cochrane
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1991 ;75:206-212
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Saunders;
1995:367-376

103
Repairof Diastematomyelia
DavidF.Jimenez and Eric Nottmeier
. Indications
. Contraindications
. Advantages
. Disadvantages
. Objective
. PatientSelection
. SurgicalTechnique
Anesthesiaand Positioning
Incision
DuralOpening and Septum Resection
Closure
.
Postoperative
Care
Tetheringof the spinal cord is an important neurosurgical
problemwhich, if untreated, may lead to significant and
progressiveneurological dysfunction. Diastematomyelia
representsone of the several clinical entities that cause
spinalcordtetheringand canbesuccessfullytreated surgi-
callyYBydefinition, diastematomyelia
is a split in the
spinalcordcaused by a bony, cartilaginous, or fibrous sep-
tumarisingfrom the ventral surface of the spinal canal.
Althoughit may be found at any level. it is most com-
monlyseen in the thoracic and lumbar spine. Recently,
Pangintroduceda unified theory of embryogenesisthat
explainsand further
describes
the different
forms of
diastematomyeliaand introduced the concept of split cord
malformationstype Iand type 11.3The spinal cord may be
cleavedinto two hemicords by the septum within a single
duralsleeve (split cord malformation type II) or may
present as two separate
and distinct
hemicords, each
withitsowndural sleeve(split cord malformationtype \)
(Fig. 103-1).
.
Indications
Patients presenting with the signs and symptoms
of a spinal
tethered cord:
. Backpain
. Scoliosis
. Urinary disturbances
.
Extremity weakness/sensory disturbance
.
Progressive orthopaedic deformities
.
Radiographic evidence of bony/fibrous septum
.
Contraindications
.
Skin breakdown or infection over the proposed surgical
sites
. Anymedicalillnessthat precludesmajorsurgery(pneu-
monia,bacteremia,etc.)
.
Advantages
.
Cord untethering
.
Halting symptom progression
.
Exploration for potential associated anamolies
759

760
Lumbarand LumbosacralSpine:PosteriorApproach
Figure 103-1
Type Isplit cord malformation.
This figure demon-
strates a bony spur extending from the ventral aspect to the dorsal
aspect of the spinal canal. Two hemicords are present. each with its
own separate
dural sleeve.
Posterior
bony elements
are often
hypertrophic and abnormal.
.
Disadvantages
. Cerebrospinal fluid (CSF)leakage
. Cord injury
.
Arachnoiditis
.
Retethering of cord
. Objective
Exposure of the spinal cord; resection of the bony. carti-
laginous. or fibrous septum traversing the spinal cord; re-
lease of spinal cord tethering and reconstruction
of the
dural sac
.
PatientSelection
Afterclinicalsuspicionhas been confirmedwith ra-
diographic studies (Fig. 103-2) the patient can be prop-
erly selected for surgical release. Toobtain the maximum
anatomical information. both magnetic resonance imag-
ing as well computed tomography should be obtained.
Computed tomographic myelography with omnipaque is
an excellent modality for demonstrating delicate soft tis-
sue. fibers. veins. and the intricate
pathological
bony
anatomy.
..-
--
I
I..
I
~'"
i,
Figure 103-2
Myelogram in a patient with type Isplit cord malfor-
mations. Note filling defect extending between L1 and L3.Thismyelo-
gram demonstrates
typical wide appearance
of the canal at the level
of the diastematomyelia.
. SurgicalTechnique
Anesthesia and Postioning
As with any spine surgery. the patients are placed in the
prone position with appropriately paddedbolstersthat
extend from the shoulder/clavicular
area to the iliac crest.
To minimize venous bleeding at the operative site.the ab-
dominal
cavity should be allowed to hang free between
the bolsters. This position will prevent retrograde venous
flow into the epidural
and spinal venous systems.thus
decreasing bleeding at the surgical site. General endotra-
cheal anesthesia
is used with
a combination
of nar-
cotics and inhalation agents. A single dose of the antibiotic
of choice (nafcillin.
cefazolin. or vancomycin) is givenim-
mediately
prior
to skin
incision
and repeated if the
procedure lasts for more than 6 hours. Extreme caremust
be taken to prevent skin pressure sores. nerve compres-
sion/stretching.
or
ocular
injury
when
the head is
placed on a cerebellar
or doughnut-shaped
headrest.
Electrophysiological
monitoring
should
be performed
and the electrodes properly
placed and tested prior to
draping.

,...
103
Repair of Diastamatomyelia
761
Incision
Thesurgeon must have thorough
knowledge of the exact lo-
cationofthe median septum and its vertebral level prior to
makinga skin incision. Localization of the appropriate
level
maybe done with fluoroscopy
or plain x-ray films. Draping
shouldallowadequate exposure of two levels cranial and
caudalto the septum.
Following dermal
incision.
electro-
cauteryis used to minimize
bleeding
as the posterior
ele-
mentsare exposed.
Intype I malformations, not uncommonly, the spinous
processesand lamina overlying the septum may be abnor-
mal.They may present with bifid or eccentric spinous
processesor dysmorphic and hypertrophic laminar arches.
Thespinous processes and lamina may be removed with
Lekselland Kerrison rongeurs in a piecemeal fashion.
Extremecare must be taken when removing the lamina
overthe septum in this type of malformation because the
traversingmidline septum is often fused with the undersur-
faceofthe lamina and the base of the spinous process
(Fig.103-3).
DuralOpening and Septum Resection
SplitCordMalformation I(Diastematomyelia. Bony Spur)
Themidlinebony septum, which is always located extradu-
rally,shouldbe left in situ after circumferentialremovalof
theoverlyinglamina is performed (Fig. 103-4). A helpful
Figure 103-3
Thisdiagramshows com-
plete L' laminectomyand partial Tl2
laminectomydemonstrating a bony spur
splitting the spinal cord and its dural
sleeves. The bony spur extends to the
ventralsurfaceofthe canal.
anatomical point for intraoperative localization is that the
septum can be consistently located where the spinal canal
is widest. A blunt dissecting tool can be used to carefully
separate the surrounding dural sleeve from the bony spur
(Fig. 103-5). Not uncommonly, the widest area ofthe bony
septum is located at its junction with the overlying lamina.
Occasionally,but not uncommonly, the septum may be ma-
nipulated as to fracture its narrow ventral base for complete
removal (Fig. 103-6A). However, most commonly it has to
be removed in a piecemeal fashion using small rongeurs or
a micro drill with diamond bur (Fig. 103-68). The septum
often contains relatively large blood vessels at its ventral at-
tachment. which frequently causes brisk and spontaneous
bleeding. Such bleeding can be easily controlled by applying
a piece of bone wax, placed at the tip of a Kittner, and gen-
tly applying pressure to the base. When using a micro drill,
the assistant should use thin brain metal bands to protect
the dura and the spinal cord from injury.
Following complete resection of the bony septum. the
dura is opened in the midline above the level of the di-
astematomyelia and the incision is carried medially along
both dural sleeves and continued caudally in the midline as
well (Fig. 103-7). Care must be taken when exploring the
medial dural sleeves because fibrous adhesions and non-
functional paramedian nerve roots may tightly adhere to
the dural sleeve. These adhesions should be sharply dis-
sected and cut (Fig. 103-8). Due to the mechanics of bone
and spinal cord growth, the septum is closely pressed
against the caudal end of the split dural sacs. Consequently,
Figure 103-4
Followinglaminectomies,
the bony spur is left in place after its at-
tachment
to the
posterior elements.
Fibrous dural attachments to the bony
spur are freed ina circumferentialfashion.

762
Lumbarand Lumbosacral Spine: Posterior Approach
Figure 103-5
Intraoperative picture demonstrating a bony spur
splittingthe duralsac intwo. Bluntdissectorsare used to carefullyfree
the surroundingduralsacfromthe bonyspurpriorto its removal.
the two hemicords are similarly tightly adhered to the cau-
dal end of the split dural sac (Fig. 103-9). Freeing of the
hemicord and dural dissection of this area is fraught with
danger and possible injury to the spinal cord.
Following resection of the dura of the ventral surface, a
dural defect may be created. Ifit is possible and easily done,
the dural edges may be approximated
with absorbable
A
B
Figure 103-6
(A) The bony spur may be removed
by fracturing
its
base and removing
it as a single unit. (8) When the attachment
is too
wide and unable to be removed in a single piece, the bony spur may be
removed
using micro drills and pituitary
rongeurs to reach its ventral
surface.
Figure
103-7
Following
resection
of the bony spur, the dural opening
is performed
as demonstrated
in Fig. 103-6.
suture. However, oftentimes it is not possible to primarily
close the dural defect, which may be left alone. (SFleaks
are uncommon due to the abundant adhesions presentven-
trally to the posterior longitudinal ligament.
SplitCordMalformation1/(Diplomyelia)
Type IIseldom demonstrates abnormal bony abnormalities
of the posterior elements,
unlike type I malformations
(Fig. 103-10). Following removal of the posterior elements,
the dural sac is seen and often the locations of the in-
tradural septa are not apparent. The dura is sharply incised
in the midline and when purely dorsal, the septum isim-
mediately exposed (Fig. 103-11). Several anatomicalvaria-
tions may be found because the septum can be locateddor-
sally,ventrally, or completely traversing the cord.Giventhat
these fibrous septa are usually thin, the cleft betweenhemi-
cords is typically small, and extensive dissection between
the hemicords
is not advocated
(Fig. 103-12).
It maybe
Figure 103-8
After the dural sac has been completely
opened, the
medial dural sleeves need to be resected flush with the ventral surface
with the spinal canal. Oftentimes
it is not necessary to repair the dural
defect of the ventral surface because abundant
adhesions to the bony
elements
preclude cerebrospinal
fluid leaks.

103
Repair of Diastamatomyelia
763
Figure103-9
Intraoperative picture demonstrating
complete resec-
tionofthe medialdural sleeves and two hemicords in place.
necessaryto expose the ventral surface by carefully rotating
thecordto one side to expose the ventral
attachment
for
sectioning.Following transection
of the septum,
the cord is
freed,and this can be corroborated
by gently
sliding
a
Woodsondental tool across the ventral surface of the cord
atthesiteofseptal attachment
(Fig. 103-13).
Figure103-10 Splitcord malformation type II.Thisaxialdiagram
demonstratesthe two hemicords found in a single dural sleeve and a fi-
brousbandtraversing from ventral to dorsal aspects of the thecal sac.
Figure 103-11
Followingdural opening. athickfibrousband oftis-
sue is seen splitting the spinal cord into two and extending into the
ventral surface ofthe canal.Thedorsal aspect ofthe bandcan be sec-
tioned and removedfollowingthis exposure.
Closure
The intradural space is irrigated with lactated Ringer's
solution and adequate hemostasis is obtained. The dorsal
aspect of the dura is closed with 4-0 Neurolon in a run-
ning, interlocking, watertight fashion. This maneuver in
split cord malformations type Ileads to the reconstitution
of the two dural sacs into a single dural tube. The epidural
Figure 103-12
Intraoperative picture demonstrating the parame-
dianfibrousband splittingthe cordasymmetricallyintwo.

764
Lumbarand LumbosacralSpine:PosteriorApproach
Figure 103-13
Following resection of the fibrous band in type IIsplit
cord malformation,
elevators can be used to gently elevate the ventral as-
pect and resect the attachment
of the fibrous band to the ventral surface
of the canal. This maneuver thus completely
untethers the spinal cord.
space is also irrigated
and careful hemostasis
of the
epidural veins is obtained with bipolar electrocautery and
Gelfoam. Valsalva maneuver is performed to ensure a wa-
References
1. BoopFA,Chadduck WM. Repair of diastematomyelia.
In: Rengachary
55, Wilkins
RH, eds. Neurosurgical Operative Atlas. Vol 3. Park Ridge,
IL: MNS:
1993:221-225
2.
Keating RF, Goodrich
JT. Tethered
cord syndrome:
management
of myelomeningocele,
diastematomyelia
and hypertrophied
filum
tertight dural closure. The paraspinous muscles are closely
approximated with 2-0 absorbable sutures (Vicryl)along
with the dorsal lumbar fascia. Marcaine 0.25%maybein-
jected into the muscle and subcutaneous tissue (maximum
dose 1 mL/kg). Subcutaneous tissue closure can be done
with 4-0 absorbable suture and the skin is closedwith
running 4-0 nylon.
.
PostoperativeCare
To minimize (SF wound leakage, the patient is main-
tained flat in bed for 48 hours. A Foley catheter is leftin
situ to improve patient comfort and to minimize moving
and sitting. In adult patients.
sequential
compression
pneumatic stocking should be used to minimize venous
thrombosis development. If significant muscular spasms
are present. Valium may be given to control pain andin-
crease comfort. Postoperative antibiotics are not routinely
or commonly used. By the third postoperative day,the
head of the bed is slowly raised until the patient isfully
sitting and tolerating
it well. The patient may be dis-
charged from the hospital when ambulating and voiding
without difficulties.
terminale.
In: Rengachary
55, Wilkins
RH, eds. Neurosurgical
Opera-
tive Atlas. Vol 7. Park Ridge, IL: MNS:
1998:211-218
3.
Pang D. Split
cord
malformation.
In:
Pang, ed. Disorders
of the Pedi-
atric Spine. New York:
Raven:
1995:203-251

104
SacralAgenesis
NatarajanMuthukumar
. Indications
. Contraindications
. Objective
. SurgicalTechnique
AnesthesiaandPositioning
TetheredCorddueto ThickenedandTautFilumTerminale
Lipomyelomeningoceleand IntraspinalLipomas
DuralSacStenosis
. Conclusions
Sacralagenesisisan underdiagnosedclinical entity. The preva-
lenceofsacralagenesisis high in certain high risk groups like
childrenwith anorectal malformations and children born to
diabeticmothers.I-3Until recently, the neurological deficits in
patientswith sacralagenesiswere considered to be due to de-
velopmentaldysgenesisof the neural elements and therefore
untreatable.However, recent experiences have shown that
certainpatients with sacral agenesis may have treatable in-
traspinallesions.2,4,SSacral
agenesismay be either partial or
total.Paradoxically,treatable intraspinal lesionsare more com-
monin partial sacral agenesis.sThis chapter emphasizes the
surgicalmanagement of common surgically correctable in-
traspinallesionsencounteredin sacralagenesis.
. Indications
. Tethered
cordduetothickenedandtautfilumterminale
. Lipomyelomeningocele
andintraspinallipoma
. Duralsacstenosis
.
Contraindications
.
Therearenoabsolutecontraindications.
. Objective
Toreleasethecordfrom lesionsthat tether it without dam-
agingfunctionalneuraltissue.
.
SurgicalTechnique
Anesthesia and Positioning
General anesthesia is used.The patient is placed prone with
supports under the chest and iliac crests (Fig. 104-1). The
abdomen should be free from compression to avoid exces-
sive epidural bleeding. Electrophysiological
monitoring
is
useful to identify
and differentiate
the functional
neural
elements from the tethering
lesions. Ultra short acting
Figure104-1
Patient ispositioned prone tak-
ingcare not to compressthe abdomen. Allpres-
sure points shouldbe adequatelypadded.
765

766
Lumbarand Lumbosacral Spine: Posterior Approach
muscle relaxants are preferred to aid in the intraoperative
electrophysiologicalmonitoring.
Tethered Cord due to Thickened and Taut Filum
Terminale
With the patient in the prone position. a vertical skin
incision is made extending from L4to the midsacral region
(Fig. 104-2). Muscles are separated subperiosteally, and
laminectomy of the caudal vertebral
elements
is per-
formed by conventional methods (Fig. 104-3A). Special
care should be taken while performing this step in all pa-
tients with occult spinal dysraphism
because unrecog-
nized defects in the bony elements can lead to inadvertent
injury to the thecal sac and its contents (Fig. 104-38). The
dural cul-de-sac is exposed (Fig. 104-04). The dura is
opened in the midline and the operating microscope is
brought into the field at this juncture. The illumination
and magnification provided by the microscope are indis-
pensable in identification and separation of the filum ter-
minale from the surrounding sacral nerve roots. In most
cases. the filum can be easily identified because it lacks the
nodes of Ranvier, which are seen in the nerve roots with
high magnification, it exits dorsally. and it has a bluish hue.
In many cases, the identification of the filum is made easier
by the fatty infiltration
of the filum. Once the filum is
identified. the next step is to separate the nerve roots that
might be adherent to it (Fig. 104-5A). Special attention
should be paid to separation of the nerve roots on the ven-
tral side of the filum (Fig. 104-58). After separation of all
the nerve roots, the filum is electrically stimulated to ver-
Figure 104-2
Theincisionismade from the midlumbarto the mid-
sacralregion.
ify that no functional neural structure is adherent orem-
bedded in it. The filum is then held separately with two
right-angled hooks, and it is cauterized at two levelsata
distance of approximately
1 cm and cut. The sectioned
filum is sent for histopathological
examination. Durais
closed watertight using nonabsorbable sutures. Themus-
cles and the skin are closed in routine fashion. It is.thepol-
icy of this author to nurse the patients in prone position
for 3 days with elevation of the foot end of the bed toal-
low adequate dural healing, even when the dural closureis
watertight.
If necessary, dural closure can be reinforced
with fibrin sealant to prevent postoperative cerebrospinal
fluid (CSF)leakage.
Lipomyelomeningocele and Intraspinal Lipomas
Inthiscondition.there isa lipomatousmassinthelowback
that passes through a defect in the fascia, muscles,andbone
to attach to the conus medullaris
(low placed)/cauda
equina. The goals of surgery in this condition are to debulk
the lipoma without damaging functional neural elements,
release the compression from the first deformed laminaand
fibrous band immediately proximal to the lipomatousmass,
and achieve watertight reconstitution of the dural sac.
With the patient in prone position, a vertical skin inci-
sion is made extending two to three segments aboveand,
if applicable. below the lesion. The skin flaps are dissected
all around the lipomatous mass to define the plane be-
tween the lipoma and the lumbar fascia. In large lipo-
myelomeningoceles. adequate care should be taken while
dissecting the skin flaps because flap necrosis can occur
with improper handling. In large lipomyelomeningoceles,
a limited debulking of the superficial lipoma can be done
at this stageto facilitatethe subsequent dissections.Once
the lipomatous mass is delineated
all around. the next
step consists of exposing the deformed lamina immedi.
ately proximal to the lipomatous mass. As the cordis
pulled dorsally by the lipoma, the cord is subjected to
compression by this deformed lamina. Therefore it ises-
sential to remove this lamina and the associated fibrous
band. The next step consists of opening the dura proximal
to the lipoma (Le., over the normal cord). The dural at-
tachment to the lipoma should be carefully separated all
around. Special attention should be paid to preservation
of nerve roots that may be attached to the dura becauseof
the rotation of the spinal cord induced by the lipoma.In
dorsal lipomas. the next step consists of debulking the
lipoma. Care should be taken to leave a thin layer ofthe
lipomatous mass adherent to the cord (Fig. 104-6A,B).No
attempt should be made to develop a plane of cleavage
between the lipoma and the cord because such attempts
will invariably produce devastating neurological deficits.
Dorsallipomasare often associatedwith thickenedfilum
terminale. which should be sectioned. Once the lipomais

104
SacralAgenesis
767
A
l
II
I
~
B
Figure104-3
(A) Muscles are separated
subperiosteally
to expose the posterior bony spinal elements.
Special care should be taken in children
withoccultspinal dysraphism because deficiency of the underlying bony element can lead to indavertent
injury to the dural and neural structures.
(8)Intraoperative
photograph
showing
the defect
in the lamina
in a case of dorsal
lipoma.
Black arrow
points
to the bony defect.
White arrow
points
to the dural defect
through
which the lipoma
enters
the thecal
sac. Failure to appreciate
this bony defect
during
subperiosteal
dissection
will lead to
neural injury.
L, lamina.
Figure104-4
Exposureofthe duralcul-de-
sac.

.
768
LumbarandLumbosacralSpine:PosteriorApproach
A
--
-
B
Figure104-5
(A) Sectioning of the fatty filum after separation of the nerve roots. Electrophysiological monitoring at this juncture greatly facilitates
the avoidanceofinadvertentneuralinjury.(8) Intraoperativephotograph showinga grosslythickenedfatty filum.Longwhitearrowpointstothefatty
filum. Short white arrow points to the nerve hook that is used to lift and separate the filum from nerve roots. Blackarrowheads point to the dura mater.
-,
,
< I
A
B
Figure 104-6
(A) In cases of dorsal lipoma with tethered
cord.
the spinal cord above and below should be exposed adequately
and the lipoma should be sectioned
from the neural element tak-
ing care to leave a thin sheet of lipomatous
tissue adherent to the
cord. No attempt should be made to establish a plane of cleavage be-
tween the cord and the lipoma. (8) Intraoperative
photograph
of a
case of dorsal lipoma
showing
a large subcutaneous
lipoma pass-
ing through
the dural defect.
White
arrow
points
to the lamina.
Black arrow points to the narrow lipomatous
pedicle. White arrow-
head points to the dural defect. 0, dura mater.

104
Sacral Agenesis
769
/
A
to.. "'-'1:4
B
Figure104-7
(A) In caudal lipomas, the lipoma should be debulked and sectioned from its attachment
to the cord. (8) Intraoperative photograph
showinga partially debulked
caudal
lipoma
being
lifted to reveal the roots
of the cauda
equina.
White arrow
points
to the dura.
Black arrow points
to
the cauda equina roots.
L, lipoma.
debulked.if possible, the normal anatomy of the cord can
berestoredby pial stitches. However, this is not always
mandatory.In caudal lipomas. where the cord inserts into
thelipomalocated in the dural cul-de-sac (Fig. 104-7A),
thelipomais transected at its caudal most extent and de-
bulked.In certain caudal lipomas, nerve roots might tra-
versethe mass and hence care should be taken to identify
andpreservethem (Fig. 104-78). Watertight dural closure
isachieved,if necessary, with autologous fascia or artifi-
cialdura. It is the author's preference to use autologous
fascialgrafts rather than artificial dura. Reinforcing the
duralsuture line with fibrin sealant is preferable because
(SFleakageis a significantand not uncommoncomplica-
tionof this surgery. The patient is then nursed in the
prone position with the foot end of the bed elevated for a
minimum of 3 days.
Dural Sac Stenosis
Dural sac stenosis is an uncommon entity.2lsolated stenosis
of the dural sac has not been reported in other conditions.
Myelographic findings are indistinguishable from tethered
cord with low lying conus and thickened filum terminale.
However, on opening the dura, all the roots of the cauda
equina are found clumped together and may even protrude
like sphagetti during dural opening. Generous duroplasty
using autologous material is a simple and effective treat-
ment (Fig.104-8).

770
Lumbarand Lumbosacral Spine: Posterior Approach
.
Conclusions
There is a high incidence of sacral agenesis in certain high-
riskgroups like children with anorectal malformations and
children born to diabetic mothers. Sacral agenesis can be
References
1.
Muthukumar N. Subramaniam
B.Gnanaseelan T.Rathinam R.Thiruthava-
doss A.Tethered cord syndrome
in children
with anorectal
malforma-
tions.j Neurosurg 2000;92:626-630
2.
Pang D. Hoffman
Hj. Sacral agenesis
with
progressive
neurological
deficit. Neurosurgery
1980:7:118-126
3.
Pang D. Sacral agenesis and caudal spinal cord malformations.
Neuro-
surgery 1993;32:755-778
FIgure 104-8
In patients with dural sac stenosis a liberal
duroplasty to enlarge the spinal theca is performed.
either partial or total. Tethering of the spinal cord can occur
inbothtotaland partialsacralagenesis:however,it ismore
common in the latter condition. A high index of suspicion
and careful attention to details will ensure a good postoper-
ative result.
4.
Muthukumar
N. Gurunathanj.
Sampathkumar
M. Gajendran
R.Sacral
agenesis
occurring
in siblings:
case report.
Neurosurgery
1992;30:
946-948
5.
Muthukumar
N. Surgical
treatment
of nonprogressive
neruological
deficits
in children
with
sacral
agenesis.
Neurosurgery
1996;38:
1133-1137

105
SelectiveDorsalRhizotomyof the
LumbosacralSpinalCordfor Spasticity
inCerebralPalsy
J.ParkerMickle
. Advantages
. Disadvantages
. Surgical
Technique
Positioningand Anesthesia
Incisionand Dissection
. Complications
. Conclusion
Thisoperation was first described by Foerster! and subse-
quentlypopularized by Fasano et aJ2and Peacock et aP and
is presently preformed
through
a narrow
laminectomy
involvingL1through SLvertebral segments. Amore limited
exposure can
be
utilized
with
the
rhizotomy
being
preformedat and just caudal to the conus medullaris.
This
procedure,however, is less accurate in localization
of levels,
and it subjects the spinal cord to a higher risk of injury.
. Advantages
. Quickprocedure takes less than 2 hours
. Lowmorbidity
. Excellentreduction in spasticity
. One-timeprocedure
. Disadvantages
. Permanent
. Significantpostoperative pain
. Long-segmentlaminectomies
. Surgical Technique
Positioning and Anesthesia
Thepatient is positioned as shown and needle electromyo-
graphic (EMG) electrodes
are placed
in the major motor
groups bilaterally (Fig.105-1). The back isshaved, prepped,
and draped for a midline incision from L1 through 52 spinal
segments. The type and level of anesthetic is important in
this procedure because the intraoperative physiology uti-
lized in this partially selective procedure can be adversely
influenced by these variables. The skin and subcutaneous
tissues are infiltrated with local anesthetic with a vasocon-
strictive agent and bleeding is much reduced in exposure if
subperiosteal and intramuscular injections of this material
are also made.
Incision and Dissection
The skin incision, subcutaneous tissue, and superficial fas-
cia are incised and the deep lumbodorsal fascia and under-
lying perispinal muscles are carefully elevated from the
underlying
spinous
processes
and
laminae
from
L1
through 51.The interspinous ligaments are left intact and
lateral exposure is limited to the most medial edge of the
facet joints (Fig. 105-2). At the cranial and caudal expo-
sure the interspinous tissues are removed with a rongeur
to expose the epidural fat at each level. A footed power
tool craniotome is then used to laminectomize both sides
from caudal to cranial. At L4and LSit is necessary to tilt
the craniotome somewhat cranially and at these points the
foot of the tool must be passed quite deeply to accommo-
date the normal lordosis in these areas (Fig. 105-3). This
technique removes a plate of laminae, dorsal spines, and
interspinal ligaments that can be replaced at the termina-
tion of the operation. The dura is opened leaving the
underlying arachnoid intact and sutured up firmly with
771

772
Lumbarand Lumbosacral Spine: Posterior Approach
EMG needle leads
Figure 105-2
Thesubcutaneous tissue andfasciaare retracted from
the spinous process. The interspinous ligaments are left intact and ex-
posure is limited laterally by the medial edge of the facet joints.
Figure 105-1
The patient isplaced inthe pronepositionon
the operating table with electromyographic needle elec.
trodes inserted into the major musclegroups ofthe lowerex.
tremities bilaterally. A midline incision is made from11
through 52.
retracting sutures. This important
maneuver minimizes
epidural bleeding once the cerebrospinal fluid (CSF)is
drained from the canal (Fig. 105-4). The arachnoid isop-
ened and the underlying nerve roots in the caudaequina
are inspected. The last large nerve root exiting through its
neural foramen is S1.S2 is much smaller. The dorsal roots
at each level are separated from the underlying and grayer
ventral root in sequence before electrophysiological test-
ing is commenced. Warm saline is used to irrigate oncethe
dura is opened. Stimulation and selection of fibers isbe-
gun at S2 on one side and in turn each root is investigated
from caudal to cranial, transecting on average 50%of fibers
at each level (Fig. 105-5). The selection criteria electro-
physiologically are controversial and vary. In our operating
room, we grade the compound muscle action potential
from 0 to 4, transecting those fibers demonstrating the
properties
of grades 2 through 4. The investigation and
transection of fibers can be performed with loupe magnifi-
cation or with the use of the microscope. In our experience,
most of the input to the spasticity in these individuals
arises from S2and S3 and we strongly recommend includ-
ing the S2 level in this operation. The risk for bladder dys-
function following this procedure including this root isa
concern but we have not seen an increased incidence of
this complication with careful selection of fibers from this
level. The dura is closed in a watertight
fashion (Fig.
105-6). Gelfoam is placed over the closed dura and the
bone can be replaced prior to closing muscle, fascia, and
skin (Fig.105-7).

105
DorsalRhizotomyfor Spasticityin CerebralPalsy
773
Figure 105-3
A drill with a footplate is used to perform the
laminectomy on both sidesfrom caudalto cranial.
Figure 105-4
The dura is opened and tacked up with sutures while leaving the underly-
ing arachnoid
intact.
The arachnoid
is opened
giving a clear view of the underlying
nerve
roots in the cauda equina.

774
Lumbar and Lumbosacral Spine: Posterior Approach
Figure105-5
The dorsal roots are separated from the ventral root in sequence before electrophysiological
testing begins. Stimulation and selec-
tion of the dorsal roots begins at 52 on one side and each root is investigated from caudal to cranial, transecting
50%of fibers at each level.
r
Figure 105-6
The dura is closed with a watertight
closure.

105
Dorsal Rhizotomyfor Spasticity in Cerebral Palsy
775
. Complications
Thisoperation can be extremely painful, but this can be
minimized with
the
placement
of
a
caudal-epidural
catheterat the time of closure (Fig. 105-7).
Once the deep
fasciais closed snugly, narcotic and local anesthesia
can be
injectedin the caudal epidural space to minimize
postoper-
ativepainand spasms. This regimen and the Foley urinary
catheterare continued for 3 days.
Asidefrom pain and spasms
postoperatively,
other
po-
tentialproblemsinclude bladder dysfunction, (SF leakage,
andprogressive spinal instability.
We have had only two
(SFleaksin 375 procedures
for selective rhizotomy. Both of
thesehad to be closed at a reoperation. Pain and spasms
can be virtualIy
eliminated
with
the
caudal
epidural
anesthetic already outlined.
We have had one male suffer
urinaryincontinence,
which
resolved
after 3 months
fol-
lowingrhizotomy. Two patients
with
preexisting
severe
lordosisin the lumbosacral
spine developed
incapacitating
painand progressive malalignment
secondary
to dif-
ferentation of the spine. Both of these
individuals
under-
wentmajor reconstructive stabilization
procedures and
bothwere older individuals
at the time of selective
rhizotomy.
. Conclusion
GeneralIy,this is an excellent operation for a properly
selectedpatient with low morbidity
and virtually no
mortality.The ideal candidate
is the 4- to 6-year-old
childwith virtualIy pure motor diplegia secondary to
prematurity.
References
1. Foerster O. On the indications
and results
of the excision of posterior
spinal nerve roots in men. Surg Gynecol Obstet 1913;16:463
1 FasanoVA,BroggiG. Barolat-Romana G.SquazziA.Surgicaltreatment
ofspasticity in cerebral
palsy. Childs Brain 1978;4:289-305
Figure 105-7
The lamina, which was removed during the opening.
may be sutured in place, resulting in a laminoplasty.
The soft tissue is
reapproximated
as well as the lumbosacral
fascia. The subcutaneous
and skin layers are reapproximated.
Acaudal-epidural catheter may be
placed at the time of closure to inject a narcotic and load anesthetic to
reduce postoperative
pain.
3.
Peacock WJ. Arens LJ.Berman
B. Cerebral
palsy spasticity:
selective
posterior
rhizotomy.
Pediatr
Neurosci 1987; 13:61-66

106
Iliac Crest Bone Grafting
Sanjay Dhall and Larry T. Khoo
.
Indications
.
Contraindications
.
Advantages
.
Disadvantages
.
Objective
.
Surgical Technique
Anesthesia and Positioning
Posterior Iliac Crest Approach
Anterior Iliac Crest Approach
.
Techniques of Graft Harvesting
. Closure
Forcases of spinal pathology associated with an underlying
degree of instability, it is necessary both to decompress the
neural elements and to fixate and reconstruct the vertebral
column. This is typically accomplished via a two-part
ap-
proach.lnstrumentation
is used to provide immediate post-
operative stability, whereas bony arthrodesis and grafting
are used to create a subsequent bony fusion. It is the solid-
ity of this osseous union that will ultimately determine the
overall stability and successof a spinal fusion procedure. All
instrumentation
systems will inevitably fail in the face of a
mobile nonunion. In specific situations such as a fibular
graft placed within
a cervical corpectomy site, the bone
graft itself can provide immediate structural support and
stability aswell.
In 1911,Albee described the first successful use of trans-
planted bony autograft in the treatment of deformity asso-
ciated with Pott's disease. To achieve arthrodesis, bone in
the form of either allograft or autograft can be employed.
Although there continues to be significant controversy sur-
rounding the risks and benefits of either, most experienced
spinal surgeonsagreethat autogenous grafts yield the high-
est rate of successful fusion. As our understanding of bone
fusion biology has progressed, this principle has also been
validated at the molecular level. Whereas allograft is only
osteoconductive, allograft bone with its bone matrix pro-
teins and mineral-collagen, is also osteogenic and osteoin-
ductive. The most common site of bony allograft used for
spinal fusions is the anterior and posterior iliac crest.
776
I
.
Indications
.
Intervertebral disk disease
.
Vertebral neoplasm
.
Vertebral fracture
.
Spinal deformity or instability
.
Spondylolisthesis/spondyloptosis
.
Bone grafting for fusion in smoking patients (relative)
.
Contraindications
. Priorgraft harvestingfrom samesite(relative)
.
Radiation or compromised vasculature of donorsite
(relative)
.
Tumorinvolvingdonorsite
.
Infectioninvolvingdonorsite
.
Lifeexpectancy< 3 months
(relative)
.
Advantages
.
The iliac crests are easily accessed from the prone, supine,
or lateral position.

. Theyare subcutaneous
with a minimum
of intervening
criticalneurovascular
structures
at risk.
. Theiliaccrests perform no vital mechanical function and are
relativelyexpendable with minimal long-term disability.
. Largereserve of both cortical
and cancellous
bone al-
lowsfor a wide variety of shapes and sizes.
. Ifa longposterior lumbar incision is planned. the approach
canbe done through the same incision by subcutaneously
elevatingthe soft tissues laterally to the iliac crest.
. Significantbone availability
. Nofear of transmissible
disease
. Osteoinductive, osteogenic. and osteoconductive
. Disadvantages
. Significantdonor site morbidity
. Neural,vascular. visceral injury
. Pelvicfractures
. Hematoma or seroma formation
. Pelvicinstability
. Cosmeticdeformity
. Infection
. Iliaccrestgraftharvestingcanbe associatedwith signif-
icantmorbidityin up to 20 to 30%of cases.
. Themostcommon sequelae include:
. Chronicpersistent pain at the graft site in up to one
thirdof patients
. Director indirect lateral femoral cutaneous nerve in-
jury with lateral thigh numbness or meralgia pares-
thetica(anterior approach)
. Director indirect cluneal nerve injury with buttock
analgesia(posterior)
. Vascularinjury of the superior gluteal artery
. Hematomaor seroma
. Pelvicinstability from sacroiliac joint disruption or
fracture
. Herniationthrough the crest defect
. Cosmeticdeformity
. Localinfection
. Objective
Toobtain an adequate
autogenous
bony graft (e.g., cortico-
cancellouswedge. strips. plugs) from the iliac crest via ei-
theran anterior or a posterior approach.
. SurgicalTechnique
Anesthesiaand Positioning
Becausethe harvesting
of iliac crest bone grafts is done as
anadjunctive procedure
to spinal fusion, the patient can be
106
IliacCrest Bone Grafting
777
either in a supine, prone, or lateral position depending on
the nature of the primary spinal operation. General anes-
thesia should be initiated in routine fashion. and the patient
positioned in the desired operative position. For anterior
iliac crest grafts taken in the supine position. it is often
helpful to place a small folded towel or other "bump" to ele-
vate and medially rotate the ipsilateral ilium superficially.
The anterior superior iliacspine (ASIS)is usually clearly vis-
ible and provides a useful reference point during position-
ing. In the prone position. no additional special preparation
is generally needed because the posterior superior iliac
spines (PSIS)are subcutaneous and typically readily palpa-
ble. As with all spinal procedures, utmost care should be
paid to properly pad all pressure points and to position the
extremities in relaxed postures to prevent traction injuries.
Prepping and draping of the iliac harvest sites can either be
done separately from the primary operative site or in con-
junction with contiguous sites during posterior or lateral
lower lumbar procedures.
Posterior
Iliac Crest Approach
SkinIncisionandMusculocutaneousFlap
The PSISis palpable under the buttock dimple in the medial
and superior portion of the buttock region. The posterior il-
iac crest then curves upward and laterally from the PSIS.Ifa
separate approach is required. an oblique incision is made in
line with the palpable iliaccrest and centered over the PSIS.
An oblique, curved, or vertical incision can be made accord-
ing to surgeon preference (Fig. 106-1). The cluneal nerves
Figure 106-1
Anoblique incisionismade in linewith the palpable
iliaccrestand centered overthe posterior superioriliacspine.

778
Lumbar and Lumbosacral Spine: Posterior Approach
also cross the posterior iliaccrest 8 to 12 cm anterolateral to
the PSISand are at risk for causing painful neuromas and a
numb buttock if injured (Fig. 106-2). Typically,if the inci-
sion is kept < 8 cm lateral to the PSIS,the nerves are pro-
tected. If a midline posterior lumbar incision has already
been done, the incision can be extended to the sacrum, and
the subcutaneous tissue and fat elevated off the lumbodor-
sal fascia laterally to the iliac crest. This plane should be
identified at the level of the midline incision and then
opened and mobilized. Asthis plane is avascular,this medial
to lateral exposure of the PSIScan usually be accomplished
bluntly under mild tension of the musculocutaneous flap.
Exposing the Posterior Iliac Crest
The fasciacan then be incised starting over the PSISextend-
ing laterally directly over the bony crest. The thickest por-
tion of the posterior iliac crest is directly lateral to the PSIS
along the posterior gluteal line along the tubercle. This area
is ideal for harvesting cancellous bone graft. The gluteus
maxim us, medius, and minimus originate from the lateral
surface of the ilium. The superior gluteal nerve innervates
the medius and minimus whereas the inferior gluteal nerve
supplies the maximus. The posterior gluteal line, which
separates the gluteus maximus and medius attachments to
the ilium, is identified. An incision is made sharply along
this line, and the muscles are then dissected off both sur-
faces of the crest. Subperiosteal dissection is performed in
the outer cortex caudally. Use of a slow-moving Bovie tip,
Surgicel,Gelfoam,and bone wax where needed is helpful to
reduce bleeding and maintain hemostasis.
Figure 106-2
If the incision is kept < 8 cm lateral to theposte-
rior superior
iliac spine, the superior
cluneal nerves are protected.
Figure 106-3
Dissection extending to the sciatic notch woulden.
danger the superior gluteal artery and sciaticnerve.

Dissectionshould not extend to the greater sciatic notch.
Thesciaticnerve and superior gluteal artery are at risk if
thedissectionis taken close to or beyond the sciatic notch
(Fig.106-3). To avoid these structures, the dissection is
keptsubperiostealand cephalad to the sciatic notch.An
imaginaryline is created from the PSISout laterally and
perpendicularto the longitudinal axis (Fig. 106-4). Keeping
thedissectioncephalad to this level protects the notch and
itscontents.After appropriate mobilization of the muscles
andperiosteum has been completed to expose the ilium,
retractorscan be placed to maintain the exposure. Because
theprimaryangle of retraction is caudal and lateral, a Tay-
lorretractorcan be placed with its point along the infero-
lateralfaceof the posterior iliac wing. Using a lap sponge
anchoredto the bed, gentle yet firm retraction of the gluteal
musculocutaneousflap can be obtained. Caution should be
exercisedto avoid placing the Taylor too deep within the
sciaticnotch.
Thekeyto safety in this approach is keeping the dissec-
tionsubperiosteal. If the dissection strays into the gluteal
musculature,excessive bleeding and injury to the neurovas-
cularstructures are more likely.Also the large vascular
structuresleave the pelvis via the sciatic notch. Laceration
ofthesuperior gluteal artery typically occurs near this re-
gionandcancausevessel retraction into the pelvis.Ifthe
sacroiliacjoint
is visualized, the dissection
has been
broughttoo medial. If the sciatic notch is visualized, the
dissectionhas been brought too distal.
106
IliacCrestBoneGrafting
779
Figure 106-4
Toprotect the sciatic nerve and superior gluteal
artery,a dissectionisnevercarriedbelowan imaginarylineextend-
ing laterellyand perpendicularto the PSIS.
Anterior Iliac Crest Approach
Skin Incision and Musculocutaneous Flap
Most commonly, anterior crest grafts are used for interbody
fusion during cervical, thoracic, or lumbosacral operations.
Likethe posterior approach, corticocancellous plugs, strips,
or dowels can be obtained. After elevation and preparation
of the anterior graft site as already described, the ASISand
adjoining crest are subcutaneous, typically visible,and eas-
ily palpable. Likethe posterior approach, the incision should
center over the iliac tubercle where the quantity of cortico-
cancellous bone is greatest. The skin incision can be made
parallel to or immediately along the crest margin.
Exposing the Anterior
Iliac Crest
The adjacent muscles include the gluteus minimus, medius,
and tensor fascia latae with their origins along the lateral il-
ial wall. These muscles are all supplied by the superior
gluteal nerve. Similarly,the abdominal musculature is also
attached to the medial wall of the ilium and is segmentally
innervated. Because there are no intervening vital struc-
tures, exposure is readily and safely achieved in a similar
manner described for the posterior iliac crest approach.
Given that the anterior crest has far less overlying soft tis-
sue and musculature, a medium-sized self-retaining retrac-
tor is typically all that is needed to maintain the exposure.

780
Lumbar and Lumbosacral Spine: Posterior Approach
..
Figure 106-5
It is important not to extend the exposure over
the anterior tip ofthe anterior superior iliacspine because separation
of the inguinal ligament from its attachment can occur, leading to
hernia.
It is important not to extend the exposure overthe
anterior tip of the ASISbecause separation of the inguinal
ligament from its attachment can occur, leading to hernia
(Fig.106-5).Furthermore,graftsshouldbetakennocloser
than one to two fingerbreadthsnear the ASIStip.Aweakly
attached ASIScan be easily avulsed by the strong actionof
the attached tensor fascia lata or sartorius muscles.Addi-
tionally, the ASISplays an important role in cosmesisas
well as in comfort with wearing pants and belts.
.
Techniques of GraftHarvesting
Depending on the nature and type of bone graft desired, the
exact
technique
of crest
harvesting
will vary. For cases
where corticocancellous
chips are desired, an osteotome can
be used to create a cortical window
below the actual crest
line. Preservation
of this outer crest margin is beneficial for
both cosmetic and functional
reasons. Longitudinal parallel
cuts are used to create corticocancellous
strips of bone (Fig.
106-6). The osteotome should be visualized carefullyduring
this maneuver to avoid making fractures through the sciatic
notch and sacroiliacjoint. Additionally,care should betaken
not to violate the inner table to decrease
the risk of postop-
erative hernia. Generally, bone harvesting from the inner
table is associated
with a higher risk of peritoneal
violation,
perforation,
and retroperitoneal
hematoma.
For cases where primarily cancellous bone graft is desired,a
much smaller "window" can be made along the iliac tubercle
in the region ofthe PSISor ASIS.Only a small exposure ofthe
crest line is made, with minimal muscular stripping, to allow
the creation
of the window. Gouges and curettes
are then
used to remove the cancellous bone from between the cortical
walls thus sparing their muscular and soft tissue attachments
(Fig. 106-7). This approach
helps to minimize
postoperative
graft site pain by decreasing
scarring and maintaining the
anatomical musculotendinous
insertions around the ilium.
When
large wedge-shaped
grafts
or plugs are needed,
careful exposure of the medial wall of the ilium shouldbe
completed
prior to bone harvesting.
Direct visualization and
Figure 106-6
Longitudinal parallel cuts are usedto
create corticocancellousstrips of bone.

theavoidanceof blind cuts are essential to prevent deep
pelvicandretroperitoneal injury and bleeding. Useof an os-
cillatingsawin such cases may also be helpful in creating
smoothparallel cuts and to help prevent microfractures,
therebyincreasingthe integrity of the graft.
Wheneverpossible, bone graft should be harvested near
thetimewhen the operative site is ready. As the harvesting
processdisconnects the graft from its blood supply, pro-
longedintervalsbetween harvesting and actual grafting can
causedessicationand ischemia of the bone. Maintenance of
thehealthand moisture of the graft are thus essential in
improvingthe chance of a successful fusion. As such, wrap-
pingofthe graft(s) in wet normal saline gauze and decreas-
ingtheout-of-body time are important surgical goals.
. Closure
Incaseswhere the crestal margin has been violated, it may
bedesirableto reconstruct the cosmetic edge with titanium
platesor mesh. Similarly, when large defects of the medial
106
IliacCrestBoneGrafting
781
Figure 106-7
Agouge isusedto removethe cancellousbone
from between the corticalwalls,thus sparingtheirmuscularand
soft tissueattachments.
iliac wall have been created, repair with mesh, plates, or
bioabsorbable materials can help to significantlyreduce the
chanceof anabdominalhernia(Fig.106-8).Reconstruction
of largecrestaldefectshas also been reported to decrease
the incidence of chronic pain due to musculotendinous
incompetency.
Meticulous hemostasis is essential in the graft site. Exces-
sive use of bone wax to control bleeding cancellous edges
should be avoided because this will retard bone healing and
has been associatedwith a higher incidenceofseromafor-
mation. Typically, the use of thrombin-impregnated
Gelfoam, Avitene, or similar substances is effective to stop
bleeding. Forlarge defects, the use of a good closed suction
drainage system is wise. The muscle and fascia are then su-
tured to their original anatomical positions. Restoration of
the musculotendinous gluteal and abdominal attachments
over some type of solid support (e.g., bone or metal plates)
is important to decrease pain and prevent cosmetic dim-
pling. The wound is then dressed in the usual fashion.
Drains should be left in until their output is minimal but
generally should not remain for greater than 2 to 3 days.
Figure 106-8
The iliacwing defect is filled with bone cement,
and malleable bladesare used to repair the iliac wall asshown.

782
Lumbarand LumbosacralSpine:PosteriorApproach
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..

Section VI
MinimallyInvasive Spine Procedures
A. Cervical
. 107. Cervical Endoscopic
Foraminotomy
B.Thoracic
. 108. Thoracic Endoscopic
Sympathectomy
. 109. Thoracoscopically Assisted Spinal
Surgery
C.Lumbar
. 110. Lumbar Chemonucleolysis
. 111. Arthroscopic and Endoscopic
Microdiskectomy via
Posterolateral Access
. 112. ForaminalEpiduralEndoscopic
Diskectomy
.
113. Percutaneous SpinalCord
Stimulator Implantation
.
114. Retroperitoneal Exposureof the
LumbarSpine
.
115. MicroendoscopicDiskectomy
.
116. MicroendoscopicDecompression
for LumbarStenosis
.
117. MicroendoscopicallyAssisted
TransforaminalLumbar
Interbody Fusion
.
118. Vertebroplasty and Kyphoplasty

107
CervicalEndoscopic Foraminotomy
LarryT.Khoo, Lacey Bresnahan, and RichardG. Fessler
. Indications
. Contraindications
. Advantages
. Disadvantages
. Objective
. SurgicalTechnique
Posteriorforaminotomy for posterolateral cervical stenosis
isasafeand efficacious alternative to anterior surgical pro-
cedures.First described
by Scoville and Frykholm
in the
late1940s,posterior cervical foraminotomy was for many
yearscommonplace among the surgical armamentarium
of
mostneurosurgeons.1-5 It allowed for direct decompression
ofthe stenotic foramen
and nerve root while minimizing
therisks of injury to the visceral and neurovascular
struc-
turesof the neck. Perhaps even more importantly,
posterior
foraminotomy does
not
result
in fusion
of the
cervical
spine,which is particularly important to the younger pa-
tient. Over recent
years,
the
popularity
of anterior
ap-
proacheshas eclipsed
the use of classical posterior
foraminotomytechniques.
As long-term
experience
with
anteriorcervical decompression has grown, so too, how-
ever,has the recognition
of its many limitations
and poten-
tialcomplications.
Itisforthese reasons that spinal surgeons are, once again,
revisitingposterior decompression for posterolateral cervi-
caldisk disease.
Theeffectiveness of posterior cervical laminoforami-
notomyfordecompressionofthe lateral recessand neural
foramenhas been well documented in numerous publica-
tionsoverthe last 4 decades.6-11When compared with stan-
dardanterior cervical techniques, the posterior approach
viaa "keyhole" type osteotomy
may provide
better
expo-
surefordecompression
of the exiting root and for removal
oflateral osteophytes
and disks.12.13For cases of isolated
radiculopathyfrom either a lateral disk or osteophyte,
93 to
97%ofpatients experienced
symptomatic
improvement
by
simplyfreeingthe nerve root via decompressive lamino-
foraminotomyand removal of either
or both the disk and
theosteophyte.2.7.10.14
Enthusiasm
for the operation
was tem-
peredby the significant cervical muscular
pain and spasm
thatoften followed. The use of wider incisions for adequate
visualizationand the need for significant paraspinous
muscle
Anesthesia and Positioning
Incision and Approach
Laminotomy and Foraminotomy
Diskectomy and Anterior Osteophyte
Decompression
Closure
dissection were blamed for this postoperative pain syn-
drome that resulted in a slower recovery course.
Microendoscopic foraminotomy (MEF) represents the
modern evolution of the classic operation with a minimally
invasive approach and high-magnification
direct endo-
scopic visualization. Developments in percutaneous surgical
access, optical technology, neuroanesthetic techniques, and
noninvasive imaging modalities have brought posterior
foraminotomy into a new millennium of spinal surgery. By
minimizing the amount of tissue trauma and muscle injury,
the MEFprocedure overcomes the limited visualization,
postoperative pain, muscle spasm, and prolonged disability
that served to limit the open foraminotomy operation.
The MEFprocedure is also able to accomplishthe same de-
gree of bony and soft tissue decompression
as open
foraminotomy.13The average proportion of facetremoval and
length of nerve root decompression can actuallybe greater in
the MEFthan in an open decompression.13.15Scoville,one of
the pioneers and early champions of the posterior lamino-
foraminotomy (LF)operation, reported excellent or good re-
sults in 95%of his patients.3-5Hiscontemporaries, adorn et al
and Raaf,reported similar good and excellent outcomes of
85%and 94%as wel1.9.10
Morerecent literature from the era of
the operating microscope has since corroborated these ear-
lier works. Henderson et al reported a 96%incidence of pain
relief after posterior LFin 846 consecutively operated pa-
tients.7 Our clinical experience with the MEFprocedure has
yielded symptomatic improvement for -87% of patients with
neck pain and 92%ofpatients with radiculopathy.15Thus MEF
yields the same clinical results as open foraminotomy with
far less tissue trauma during the approach.
Aword of caution is needed. Microendoscopic techniques
such as MEFdo involve a very steep learning curve that
must be diligently overcome. The two-dimensional
view
and hand-eye spatial separation of the technique can be ex-
tremely disorienting at the beginning. The operation should
785

786
Minimally Invasive Spine Procedures: Cervical
~
be first learned in the safe confines of a surgical teaching
laboratory in cadavers. Only after one has become comfort-
able with the endoscopic technique should one perform the
MEFin the operating theater. Assuch, a significant amount
of time is requisite before any surgeon can gain facility with
this procedure. This steep learning curve, however, is well
justified when one considers the many benefits to the pa-
tient. Compared with open foraminotomy, the MEFtech-
nique offers significant reductions in operative blood loss,
length of hospital stay, and postoperative pain and disabil-
ity,lSPerformed safely and correctly, the cervical MEFis a
paradigm of outpatient spinal surgical procedures.
"Theseaisdangerousandthestormsterrible.but theseob-
stacleshaveneverbeensuffidentreasonto remainashore., ."
(Ferdinand Magellan c. 1520).
.
Indications
.
Posterolateral "soft" disk herniation
.
Posterolateral "hard" disk herniation
.
Posterolateral osteophytic and spondylytic disease
.
Cervicallateral recess stenosis
.
Cervicalforaminal stenosis
.
Hypertrophy or buckling of ligamentum flavum
.
Facetarthropathy with foraminal compression
. Smallbenign extradural lesions of the recess and foramen
.
Contraindications
. Cervicalmyelopathy
.
Largecentral disk herniations
.
Central stenosis (acquired or congenital)
.
Centralosteophytic or spondylytic disease
.
Ossificationof the posterior longitudinal ligament
.
Severekyphotic deformity
.
Subluxation or spondylolisthesis (relative)
.
Cervicalspinal instability (acute or chronic)
.
Primaryor metastatic tumor
.
Osteomyelitisor other infection
.
Pseudomenigocele or cerebrospinal fluid (CSF)fistula
.
Advantages
.
Avoids risk of injury to anterior neurovascular and vis-
ceral structures
.
Easysurgicalapproachwith minimal trauma to dorsal
muscle and fascia
. Decompression under direct visualization of root along
its entire length
.
Maintains stability of motion segment if < 50%facet
removed
.
Avoidsfusion and risk of adjacent-level degeneration
.
Preserves mobility of the motion segment
. Decreasedblood loss,hospitalstay,postoperativepain
.
Disadvantages
. Limitedabilityto addressanteriorpathology
. Inabilityto dobilateralposteriordecompression
.
Inabilityto fuse motionsegment forcasesofinstability
.
Inabilityto correct cervicalalignment for kyphosisor
deformity
. Steeplearningcurveofendoscopicspinaltechniques
.
Objective
Toobtain a minimally invasive, fluoroscopically guided per-
cutaneous
access to the level of the pathology and to
directly decompress the nerve root along its course in the
lateral recess and neural foramen by completing a lamino-
foraminotomy and also a diskectomy if needed.
.
SurgicalTechnique
Anesthesia and Positioning
Following the induction of general endotracheal anesthesia,
adequate intravenous access is secured. Local anesthesia
combined with intravenous sedation is inadequate formost
cases of MEFbecause there is a substantial risk of injuryto
the spinal cord and nerve roots should there be anyacci-
dental movement during the procedure. During our initial
experience with the MEFtechnique, we positioned the pa-
tients prone on either standard chest roles with aJacksonor
a four-poster frame. In our last 13 cases, we adopted a sit-
ting position with a Mayfield headrest, which significantly
improved visualization, relieved epidural venous conges-
tion, and decreased operative blood loss (Fig. t07-tA).
For the purpose of this text, the sitting position will be
assumed.
After positioning the patient, utmost care should be di-
rected to ensuring that the cervical spine and neck muscu-
lature are not kinked or held in an unfavorable position.The
neck, chin, and chest must be allowed to remain loose and
free of compression. Forthe first several cases performed in
the sitting position, a central venous pressure (CVP)
catheter was placed into the right atrium in anticipation of
blood loss and possible venous air embolus. Precordial
Doppler monitoring was also used to detect such air emboli
within the atrium. Asour facility and experience with this
surgical technique has grown, we no longer routinely place
a CVPcatheter due to the brevity and minimal blood lossof
the operation. To date, we have had no cases of sympto-
matic air embolus during the MEFprocedure. Similarly,we
do not typically place a Foleycatheter for routine cases.We

....
I
107
Cervical Endoscopic Foraminotomy
787
)
A.
- '::ii;'," JI':':':a;
_:,
I
-'II'
iI
i 11I8:...
B
Figure107-1
(A) Patient in sitting position with Mayfield headholder and fluoroscope in place. (B) Surgeon standing behind patient with microen-
doscopicapparatus in place.
routinelyutilizeintraoperativesomatosensoryevokedpo-
tential(SSEP)monitoring of the operated dermatome as
wellas of distal distributions
to examine spinal cord
integrity.Electromyographic recordings (EMGs)can also be
usedtoassess motor integrity of the involved root. After the
initialinduction of anesthesia,
we have refrained from
theuseof neuromuscular paralytics to allow for improved
feedbackfrom the nerve root during the operation.
Formost cases, a single intraoperative dose of either An-
ceforvancomycin is used. We do not routinely employ Sol-
umedrolor other glucocorticoids for neural protection dur-
ingMEFprocedures. The fluoroscopic (-arm is brought into
thesurgicalfield so that real-time lateral fluoroscopic im-
agescan be easily obtained. Anteroposterior (AP) fluoro-
scopicimages can be obtained during initial Steinmann pin
localizationif additional confirmation in the coronal plane
isdesired.The surgeon generally stands directly behind the
neckofthe patient.Thevideomonitorsaretypicallyplaced
onthe patient opposite of the operative side. However, the
ultimatearrangement
of the video monitor and (-arm
monitorshould be varied to allow for optimal ergonomic
flowduringthe procedure.Fig.107-18demonstratesanex-
ampleof this operative arrangement with a closeup view of
theendoscopicapparatus in place as it would appear during
theprocedure(inset).
Incisionand Approach
Astabincision is initially made -1 cm off midline ipsilat-
eralto and at the level of the pathology. Under fluoroscopic
guidance,a thin Steinmann pin is inserted through the pos-
teriorcervical musculature and fascia down to the facet or
lateralmass of the target level. Particular caution should be
takenat this point to ensure that the guidewire is docked
onboneto avoid inadvertent dural penetration. It is better
toerrlaterallyduring this docking maneuver to prevent en-
teringthe sometimes wide interlaminar space. Ideally, the
pin should rest at the spinolaminar junction on the medial
edge of the facet complex (Fig. 107-2). Although we have
not routinely done so, AP radiographic images can be ob-
tained
to guarantee
proper pin positioning.
Once the
guidewire is docked on the facet in question, the skin inci-
sion is extended above and below the Steinmann pin for a
total length of -2.0 cm. The skin edges are retracted and
the cervical fascia is incised using Metzenbaum scissors.
(are should be taken not to cut muscle fibers during this
procedure because this can cause unnecessary blood loss.
This sharp opening of the fascia allows for easier passage of
the sequential dilating cannulas with a minimum of force.If
a barrier such as loband has been placed on the skin, it
should be dissected away from the skin edges to prevent
plastic sequestra that can occur during placement of the
percutaneous dilators.
The series of dilators are then sequentially inserted
through the neck soft tissues, over which a 16 or 18 mm
tubular working channel is then inserted (Fig. 107-2D).
Real-time lateral radiographic images should be obtained as
often as needed to insure a proper working trajectory
throughout
this process (Fig. 107-2A-C). The working
channel (tubular retractor) is then attached to a flexible re-
tractor affixed to the operating table side-rail and locked in
position at the junction of the lamina and lateral mass. The
endoscope should be white-balanced and an antifog agent
applied to the lens. It is then attached to the tubular retrac-
tor via the circular plastic friction couple. We employ the
METRxsystem(MedtronicSofamor-Danek;Memphis,TN)
of endoscopic retractors, camera, and instruments for our
MEF procedures (Fig. 107-3). Because this system was
initially designed for lumbar diskectomy, several modifica-
tions have been made to better optimize its use in the
cervical MEFprocedure. These include lengthening of the
table-mounted
retractor as well as a better selection of
smaller profile dissectors and Kerrisons for use in the more
delicate cervical spine. Additionally, the endoscopic camera

788
MinimallyInvasiveSpine Procedures: Cervical
Figure 107-2
Lateral radiographic images demonstrating (A)the
placement of the Steinmann
pin down to the junction
of the lateral
mass and lamina over the (4-(5
foramen. (B) Sequential
passage of
the metal dilators allows for a minimally traumatic
spreading of the
posterior cervical muscles off the surgical area. (C) The final 18 mm
tubular retractor is then put into position to provide the final surgical
exposure. (D) Illustration depicting
serial dilators in dorsal muscula-
ture of cervical spine.
used today has far superior resolution and clarity than the
cameras used during our previous cadaveric studies and ini-
tial operative cases.Further modifications of the tubular re-
tractor and surgicalinstruments are ongoing.
Laminotomy and Foraminotomy
Once the tubular retractor is set in the desired position
(Fig. 107-4A), a Boviecautery with a long tip is used to re-
move the remaining muscle and soft tissue overlying the
lateral mass and facet. It is best to begin this dissection lat-
erally where the bone is clearly felt.The dissection can then
be continued medially to expose the laminofacet junction,
with care being taken not to slip into the interlaminar space
at this point. Often the ligamentum flavum is thinned oral-
together absent near the lateral edge of the interlaminar
space, thereby placing the dura and spinal cord at higher
risk. With the bone well visualized, a small straight endo-
scopic curette is used to scrape the inferior edge of the su-
perior lamina and the medial edge ofthe lateral mass-facet
complex (Fig. 107-48). This exposure is then carried under-
neath the lamina and facet with the use of a small angled
endoscopic curette. This curette is used to hook under the
lamina and to free the soft tissue from its periosteal attach-
ment. Proper placement of the curettes can be confirmed
under fluoroscopy to double check that it is indeed under
the lamina of the correct level (Fig. 107-4C). Gooddissec-
tion of the underlying flavum and dura from the bone de-
fines the relevant anatomy and helps to prevent incidental
dural tears. Bleeding from epidural veins and the edgeof
the flavum is controlled via a long-tipped endoscopic bipo-
lar cautery. Forbleeding underneath the edge of the lamina,
angled bipolar forceps with a 45 degree angle are often use-
ful. After the plane has been clearly defined, a small angled
endoscopic 1 or 2 mm Kerrison rongeur is utilized to begin
the foraminotomy (Fig. 107-5A). Periosteal and bone bleed-
ing is addressed with bone wax and cautery. In cases of
marked facet arthropathy and enlargement, a drill with a
long endoscopic
bit (e.g., AM-8 bit with
Midas Rex
(Medtronic, Minneapolis, MN] or TACbit with MEDNext
drill) can be used to further thin the medial facet and lateral
mass (Fig. 107-58). Often the lamina can be oriented in
quite a vertical fashion making it difficult to bite it witha
Kerrison punch. In such instances, it is best to use a drillto
simultaneously thin and flatten the lamina down. Frequent
dissection of the soft tissue off the bone with an angled
curette facilitates safe use of the Kerrison rongeur (Fig.
107-5C,D). In this fashion, the decompression is carefully
continued inferiorly and laterally along the course of the
neural foramen (Fig. 107-5E). The laminoforaminotomy is
completed when the nerve root has been well exposed
along its proximal foraminal course. The adequacy of the
decompressionshould be confirmedbypalpatingthe root
along its course with a small nerve hook (Fig.107-5F).
Diskectomy and Anterior Osteophyte
Decompression
For cases where a herniated disk is present, either a nerve
hook or small no. 4 Penfield is used to mobilize the nerve
root superiorly to expose the disk space and fragment. For
this maneuver, additional exposure can be obtained by
drilling a small portion of the superomedial portion ofthe
pedicle directly below the exiting nerve root. Because the
nerve root lies directly against this portion of the pedicle,
removing it will create space for the root to be mobilized.
With the root retracted, the disk fragment is then removed
in a standard fashion with curettes and long endoscopic pi-
tuitary rongeurs. Additionally, osteophytes encountered in
this region can also be drilled or curetted as needed. Down-
biting or downpushing
curettes (e.g., Epstein curettes)
can be used to reach anteriorly around the nerve root
and dural margin. With gentle pressure and use of a mallet,