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Idiopathic
Spinal cord herniation is a rare cause of myelopathy. However, this condition
is been increasingly recognized. We describe a case report with a supplemental
intraoperative video and review the pertinent literature.
INTRODUCTION
Case Report
A 53 year lady presented with history of tingling and numbness
involving left lower limb, weakness of lower limbs which was more pronounced on
the right side and gait instability. She reported a gradual worsening of
symptoms since two years, which had become more conspicuous in last six months
and needed a stick to ambulate. She also noticed that she was unable to
perceive any temperature sensation in her left lower extremity but never had
any bowel or bladder irregularity. She had no other co morbidity or prior
surgery. On examination there was decreased tactile and pin prick sensation and
reduced temperature perception in left lower limb. The joint position and
vibration sense was impaired in bilateral lower limbs. Weakness in right lower
limbs was more at distal extremity. The knee and ankle reflexes were diminished
bilaterally. The
neurological evaluation was suggestive of a Brown-Sequard syndrome at the level
of T4. MRI of the dorsal spine
suggested an anterior displacement of the spinal cord with a characteristic
kink (Figure 1).
The herniated spinal cord was seen in the axial MRI. With the patient
in prone position, using motor evoked potential (MEP) and somatosensory evoked
potential (SSEP) guidance, a T3-5 laminectomy was done and a midline durotomy
was performed and the dentate ligaments were sectioned. The anterior displacement of the spinal cord
was visualized and the defect in the anterior dura was identified. The defect
was increased in size to release the herniated spinal cord from the adhesions
and the herniated cord was gently reduced(Figure
2.). All these maneuvers were guided by intraoperative electrophysiological
monitoring. After ensuring complete reduction of the ventrally herniated cord
at T4 level, the defect in anterior dura was carefully delineated and repaired
with autologous fascia (onlay patch). The cord was slightly atrophied and the
subdural space was capacious, hence the dura was closed primarily (Video 1.). The postoperative course
was uneventful and the patient improved symptomatically within 3 weeks of
surgery. With continuing physiotherapy and gait training her walk improved
significantly. At 3 months, she could walk around with very minimal support
with significant improvement in her sensory perception. Her postop MRI showed
complete reduction of the herniated cord (Figure
1).
DISCUSSION
1. Pathogenesis
Presence of a dural defect is the pathognomic feature of this
condition. There are three theories regarding the pathogenesis of this dural
defect. (Table 1.) Aizawa and
coworkers described 3 types of ventral dural defect: (a) a defect in the inner
layer of the duplicated ventral dura; herniated spinal cord is covered by an
outer layer of dura (b) direct epidural spinal cord herniation through a
full-thickness dural defect and (c) an
epidural cyst or pseudomeningocele [11].
Irrespective of
the reason of dural defect, it is believed that the spinal cord attempts to
plug the defect initially and eventually spinal cord herniation occurs due to
the CSF pulsations. This is followed by adhesions at the site of defect, which
“tethers” the cord and causes vascular compromise and subsequent myelopathy.
The limited motion in the thoracic spine, the anterior position of the thoracic
cord, the physiological thoracic kyphosis and the physiological anterior motion
of the spinal cord with cardiac and pulmonary movement may facilitate this
process [12].
2. Imaging
MRI is the gold standard technique for diagnosis of ISCH. However
misdiagnosis is extremely common and has been reported in 21% of cases in
literature [13]. The most common “cause” of misdiagnosis was a dorsal arachnoid
cyst.
In MRI, typical features of ISCH [14] are as follows
1. Ventral displacement,
2. Sharp ventral angulation of thoracic spinal cord,
3. Enlargement of dorsal subarachnoid space
4. Attachment of the herniated spinal cord to the ventral dura with
complete obliteration of intervening CSF space.
ISCH has been classified based on sagittal imaging into three types
according to the severity of herniation and displacement: Type K (kink),
showing a ventral spinal cord kink; Type D (discontinuous), showing complete
spinal cord disappearance at the herniated site; and Type P (protrusion),
showing obliteration of anterior subarachnoid space no or minimal kink [15].
These types may represent different stages in the development of ISCH.
Phase-contrast MRI can be crucial in excluding a posterior compressing
arachnoid cyst and may replace computed tomographic myelography [14]. In
ISCH, the spinal cord is frequently shifted ventrolaterally and sometimes
rotated toward the side of tethering. Tethering of the spinal cord at the side
of the herniation results in unilateral damage of the lateral funiculus and
might cause symptoms of Brown-Sequard syndrome. Occasionally bone defect due to
the ISCH has also been reported [15]. Some of the other atypical signs include
the nuclear trail sign, presence of T2 hyperintensity in the cord or the
presence of a syrinx [16].
3. Management
Surgery is the treatment of choice for reversing or stopping the
progression of serious neurologic deficits. Intraoperative electrophysiology is
an important adjunct. A combination of MEP and SSEP is usually preferred for
these cases [2]. Laminectomy with sectioning of the dentate ligaments and
gentle rotation of the cord is usually adequate to visualize the herniation.
Occasionally these maneuvers may not suffice and in those cases, posterolateral
bone removal (facetectomy or costotransversectomy or transpedicular
approach)may be performed to performed to gain access anteriorly or
anterolaterally [12]. This additional bone removal may also be necessary in
cases with persistent intraoperative electrophysiological changes.
There are 3 main treatment strategies to manage the dural defect:
(a) Primary closure of dural defect
Wortzman first performed primary suturing of the dural defect in 1974
[1]. However there is not enough space to pass the needle for primary suture.
This procedure increases the risk of spinal cord damage.
(b) Duraplasty after reducing the spinal cord
Duraplasty is a more commonly used technique first described by
Masuzawa and coworkers in 1981 [17].Some of dural substitutes which were used
are muscle fascial flap, fat, lyophilized dura, and gortex membrane [18]. Some
authors have performed duraplasty, even when there is evidence of dural duplication
[19]. Arts et al. have proposed the use of a dural graft to wrap the spinal
cord and thus to prevent future re-herniation [20].
(c) Enlargement of the dural
defect to prevent cord strangulation.
The technique was first described by Nakazawa and was performed by the
authors, who proposed “dural duplication” as the cause of spinal cord
herniation [3]. It must be emphasized
that reduction of the spinal cord should be performed first before enlargement
of dural defect is carried out to prevent neurological deterioration [6]. This
technique is easier and requires less traction of the spinal cord than repair
of the dural defect. However, anterior cerebral spinal fluid collection is a
complication after this procedure, though they are rarely symptomatic.
Some authors in the past have also performed a biopsy of the herniated
cord with a suspicion of a malignancy due to the reddish appearance of the cord
[21, 22]. Postoperative syrinx has also been reported in two patients out of
seven patients in a caseseries. These authors have therefore recommended an
expansile posterior duraplasty to ensure circulation of the CSF [12].
Recurrence of herniation has also been reported infrequently [23].
There are a total of 15 cases reported in literature where the patients
have been treated in a non-operative manner [13]. Conservative management may
be possible in patients with mild or non-progressive neurological deficits.
These cases have shown stabilization of their neurological deficits without any
improvement or worsening [13].
4. Predictors of outcome
The outcomes for
patients who initially presented with Brown-Séquard syndrome were better than
for patients with spastic disorders (paralysis, paraparesis, and monoparesis)
[2]. Groen et al in their meta analysis also reported that the patients
undergoing release of the spinal cord and enlargement of the dural defect had
the best outcome in terms of motor function [2]. Barbagallo et al stated that
outcome was less favorable for spinal cord herniation at a vertebral body level
than for disk-level herniation [24]. Presence of bony defects and T2
hyperintensities in the preop imaging has also been suggested as a predictive
factor for severe preoperative symptoms as well as poor postoperative outcomes
[21].In a review of 159 patients, it was reported that 74% improved after
surgery, 18% had stabilization of their neurological deficits and 8%
deteriorated after surgery [13]. Recurrence of herniation has been reported in
a patient even after 10 years of surgery and hence long-term surveillance is
recommended [25].
CONCLUSION
ISCH is a rare
cause of myelopathy, which is being increasingly recognized with advances in
imaging and improved awareness. Reduction of herniation and duraplasty to
repair the dural defect is a safe and effective method to improve the
neurological status in patients with Brown-Sequard syndrome.
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