Split Spinal Cord Definition - PowerPoint Presentation

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Split Spinal Cord

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Definition

the presence of a longitudinal cleft within the spinal cord

across one or more vertebral segments.

Type I malformations (formerly diastematomyelia) are characterized by a bony septum that cleaves the spinal canal in the sagittal plane and a duplicated thecal sac.

Type II

malformations (formerly diplomyelia) are characterized by a cleft

cord within a single dural sac, often tethered by a fibrous midline

septum to the adjacent dura

.

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S

ingle error

in embryogenesi

s

adhesion between the ectoderm and endoderm

leading to a persistent neurenteric canal.

SCMs are accompanied by nonfunctional

paramedian nerve roots traveling within a fibrovascular bundle

to or beyond the dura.

fibrous tract extending from the epidural

space to a small overlying plaque of atretic skin may also be

present.

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SCM is often

heralded by characteristic cutaneous and orthopedic findings.

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EPIDEMIOLOGY

Incidence

3.8% to 5% of all congenital spinal

anomalies

.

The prevalence of SCM is estimated to be 1 in 5000(0.02%) live births.

S

light female preponderance, approximately 1.3 : 1

.

peak age at initial medical evaluation is 4 to 7 years, although there is a second peak between 12 and 16years of age.

T

ype I SCMs occur more frequently

than type II lesions.

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The most common associations (in descending order) are tethered/low

lying cord (>50%), kyphoscoliosis (44% to 60%),syringomyelia (27.5% to 44%), and other forms of spinal dysra-phism such as thickened or fatty filum, dermoid cyst, dermal sinustract, neurenteric cyst, and spinal lipoma (11% to 26%)

.

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When SCM in association with myelomeningocele

three to four

times more likely to be a type I malformation and tends to occur

at or just rostral to

level

o

f

the

myelomeningocele

defec

t

.

Diastematomyelia is most commonly encountered in the

lumbar region, followed by thoracolumbar, thoracic, and cervical

regions, and occurs over an average of six vertebral levels

.

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EMBRYOGENESIS

SCMs are thought to occur during the third week of embryogenesis, concurrent with gastrulation, as a result of failure of fusion

of the notochord in the midline and subsequent persistence of an

accessory neurenteric canal.

P

ersistent adhesion of the

ectoderm and endoderm, which called an accessory neurenteric canal.

A

cleft notochord, with subsequent

induction of a cleft spinal cord.

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SIGNS AND SYMPTOMS

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IMAGING

The cardinal feature on MRI

is the presence of two hemicords, which are best visualized on

T1-weighted sequences

.

The cleft begins

below T11, and the hemicords most often reunite after two tothree vertebral segments.

A

ssociated fatty filum

Associated tethering anomalies

.

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IMAGING

proper categorization of the

malformation as type I (with an associated “owl sign” on MRI

or

type

2 on T2 MRI.

T2-weighted axial and coronal images

may also demonstrate a hypointense fibrous band in type II SCM.

In type I malformations, computed tomography (CT) best

delineates the configuration of the osseous spur.

The more common bony segmentation defects include

bifid vertebrae, bifid laminae, Klippel-Feil malformation, butterfly vertebrae, and hemivertebrae.

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IMAGING

Hypertrophic

arches are often fused to the lamina of an adjacent segment, a

condition referred to as intersegmental laminar fusion. When associated with bony spina bifida (60% of cases), this finding is virtually pathognomonic for type I SCM

.

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SURGICAL MANAGEMENT

The presence of a type I SCM is often taken as indication

for operative intervention.

By contrast,many surgeons elect to serially obser

v

e

ne

urologically and urologically asymptomatic patients in whom type II SCM is discovered incidentally or as a result of the presence of a cutaneousmarker only.

G

oal is to untether

the spinal cord by operative management of both the SCM and

any associated tethering anomalies.

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Surgical repair of SCM performed in conjunction with intraoperative electrophysiology, including continuous somatosensory evoked potential

monitoring of the extremities at and below the malformation,motor evoked potential monitoring, or electromyography and

anal sphincter monitoring

.

The patient is positioned prone after a Foley catheter is

placed.

SURGICAL MANAGEMENT

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Care

must be taken during midline exposure to avoid durotomy and neural injury given the high incidence of concomit

a

nt

neural arch defects.

The operation begins

with bilateral paraspinous muscle exposure generally extending

one to two levels above and below the SCM to allow dissection

to extend from normal to abnormal anatomy.

SURGICAL MANAGEMENT

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Rongeurs or a high-speed drill (or both) should then

be used to perform bilateral paramedian laminectomies, while

preserving the midline lamina and spinous process and thus preventing any torque or lateral force from disrupting the bony spur

prematurely

.

Once the spur is isolated and exposed, blunt subperiosteal dissection may be performed to separate the dural sleeves

from the spur bilaterally.

Once freed, the spur may be resected carefully with a small

rongeur or high-speed drill.

SURGICAL MANAGEMENT

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Under magnification, the dura is opened sharply in the midline

above and below the lesion and on either side of the split at the

level of the duplicated dural sleeves

.

Sharp dissection can be used

to free the hemicords from their medial attachments to the dural

sleeves.

Once freed, the central dura can be sharply resected

to the level of the posterior longitudinal ligament ventrally to

restore the normal configuration of a single thecal sac

.

SURGICAL MANAGEMENT

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Any associated tethering lesion (sinus tract, fatty filum, or

terminal lipoma) should also be addressed.

Any additional tethering bands should also be transected so that both hemicords and the conus can move freely within the spinal canal.

Dorsally, the dura is

closed in watertight fashion, if

necessary, with a dural patch.

The patient should be kept flat postoperatively for 1 to 2 days

to allow a preliminary seal to form along the dural suture line.

SURGICAL MANAGEMENT

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OUTCOMES

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