INTRODUCTION
The
general term "spinal dysraphism" refers to those congenital
malformations involving any or all of the tissues on the mid-line of the back.
It was initially introduced by Lichtenstein in 19401. The exact
incidence of these lesions is not known with clinical estimate of 4–8/ 10,000
reported in some studies2.
Two
forms of spinal dysraphism exist: a closed form "spina bifida
occulta" and an open form "spina bifida aperta". In spina bifida
occulta the skin overlying the spinal anomaly is intact and no neural tissue is
exposed. This group includes dorsal dermal sinus, caudal regression syndrome,
diastemato-myelia, tight filum terminal, intradural lipoma, syringohydromyelia
and anterior sacral meningocele3.
The tethered cord syndrome (TCS) is not some sort of
malformation. Instead; it is a clinical syndrome that may ensue as a
complication of myelomeningocele repair or as the presentation of occult spinal
dysraphism4. TCS involves traction on a low-lying conus medullaris
with progressive neurologic deterioration due to metabolic derangement5.
The age
of presentation of TCS ranges from early childhood to the elderly. The
presentation differs according to the underlying pathology including: back and
leg pain, cutaneous signs, weakness, gait deterioration, foot deformities,
progressive scoliosis and sphincter dysfunction6,7.
Early
surgical untethering should be considered upon diagnosis of asymptomatic or
symptomatic spinal dysraphism. It has the greatest chance of restoration of
neurological function8,9.
These
findings prompted us to evaluate our current clinical practice and set out the
following study goals. First; to give a detailed description and to analyze the
clinical, urodynamic, Somatosensory evoked potential (SSEP) and MRI findings in
patients with occult spinal dysraphism. Second, to examine the validity of our
multidisciplinary team evaluation in selecting children for untethering before
the inception of progressive irreversible neurological deficits.
SUBJECTS
AND METHODS
From January 2006 to January 2011, 10 children with occult
spinal dysraphism attributable to various pathological conditions were referred
to the department of neurosurgery Suez
Canal University Hospital. The following children were
included: Asymptomatic children with cutaneous stigmata, or those presented
with symptoms and signs of spinal dysraphism; no history of previous surgery;
age <12 years.
Pre-operative assessment of Neurological dysfunction (Back
pain, sphincter dysfunction, weakness or atrophy of the lower limbs),
Orthopedic deformities (Pes cavus, Talipes equines, equinovarus) and Urological
dysfunctions (Urinary incontinence, abnormal urodynamic studies, complications
of chronic urinary retention e.g. hydronephrosis) were recorded.
Urodynamic
tests examination (laborie, Ontario
Canada)
were done with special attention to bladder hyperreflexia10. In urodynamic
tests, compliance and capacity of the bladder, leak point pressure, and
uroflowmetry were recorded. Bladder hyperreflexia was considered to be the
major indication for surgery.
Somatosensory
evoked potential (SSEP) examinations by neurologist (Dantec key Point TM
apparatus, Denmark)
were evaluated searching for indicated for surgery with relatively normal
clinical examination. Posterior tibial SSEP was used. Delay in N22 wave
latency, low amplitude, blockade of conduction was considered to be
pathological8.
MRI was done for all the patients. All had low lying coni
medullari. Tight filum terminal was
considered by the presence of a short filum with conus medullaris below
L2. A thick (fatty) filum was defined as
a filum diameter >2 mm11 (Figure 1). Fatty lipoma within a
thickened filum terminale is a stripe of increased signal intensity on sagittal
T1-weighted images. In lipomyelo-meningocele, sagittal T1-weighted image shows
high signal intensity subcutaneous lipoma creeping through a wide posterior
bony spina bifida into the spinal canal to connect with the low lying spinal
cord (figure 2). Dermal sinuses are easily recognized on mid sagittal MRI as a
thin hypointense stripe crossing the subcutaneous fat. Associated anomalies such
as Chiari malformation, syringomyelia and/or hydromyelia, scoliosis, and
vertebral anomalies were also considered9.
Operative and
postoperative outcome:
During
surgery and after laminectomy, filum terminal was known as microscopic aspect
of the filum including; midline posterior position, tension and retraction
after section, thick and fatty aspect, serpentine vessel on its surface, its
pallor as compared with the nerve roots, and usually thick than 2mm9.
Untethering is achieved simply by dividing the tight filum terminale. (Figure 1-F)
For lipomyelomeningoceles, untethering procedures consist
of dissecting and debulking the lipoma upon the lumbodorsal fascia, laminectomy
on the lower lumbar spine according to the level involved, and opening the Dura
for exposing the intradural portion of the lipoma. The junction between the
lipoma and the neural placode is dissected and divided for untethering. The
lipoma was subtotally excised to allow the neural placode to move freely within
the spinal canal, and any tethering arachnoidal adhesions were divided.
After the subtotal resection of the lipoma, the pia was
closed if possible and the filum terminale was divided to release any potential
tethering (Figure 2). Successful intraoperative untethering is defined as the
conus medullaris retracts rostrally for at least one level of lamina. When the
cerebrospinal fluid (CSF) space seems inadequate, patches of dural substitute
were used. After satisfactory hemostasis, the wound was closed in layers.
Post-operative complications were reported.
Post-operative:
Patients were maintained in a prone position for 5 days. When the patients had
no signs of CSF leakage, they began to mobilize. In case of CSF leakage or
infection, further beds redden days were considered till the wound become
clean.
During
follow-up period; urodynamic and SSEP were evaluated post operatively 6 months
while clinical evaluation was extended thereafter for assessment of improvement
after surgery. Comparison was made between the pre and post-operative data.
Data were presented as mean ± standard deviation (SD), and
considered significant when the two-tailed P value was <0.05.
Differences in dichotomous outcomes preoperatively versus postoperatively were
assessed using the chi-square test and the Fisher exact test.
RESULTS
Ten children with tethered cords attributable to various
pathological conditions were included. Their ages ranged from 1 month to 7
years. Seven patients (70%) were females and 3 (30%) were males. All had
cutaneous stigmata. Five patients did not have primary toilet training; the
rest were toilet-trained for various periods of time, but then showed
deterioration in their bladder function. Three patients had back pain (30%) and
one patient had leg pain (10%). All the patients (except one) had normal motor,
sensory and reflex functions in their lower extremities. This patient had
distal weakness with equinovarus deformity of foot (Table 1).
Urodynamic
tests were performed in nine patients but one patient with dermal sinus was
operated early at the age of one month. Bladder hyperreflexia was considered to
be the major indication for surgery in five patients (Table 3). Three patients
had evidence of delay or block at posterior tibial on SSEP, five were normal,
and two had difficulties in recording. Definitive diagnosis was made on MRI. No
patient had associated congenital anomalies as syringo-hydromyelia, split
notochord syndrome or anterior sacral meningocele.
All the patients had untethering. Resection of the lipoma
was incomplete in two patients with transitional type of lipomyelomeningocele
but we were able to close pia in one case (Figure 2-D). One case of
lipomyelomeningocele needed further dural patches during closure. Although Dura
was tightly closed in all cases, we had five children (50%) with CSF leakage.
Two patients (20%) had persistent leakage that mandate subcutaneous catheter
drainage above the incision line and improved after two weeks. One patient
(10%) had skin infection due to primary skin sinus and improved with time, one
patient with transient foot drop for two months, and lastly one patient (10%)
had transient urine retention due to conus manipulation in case with caudal
conus lipoma (Table 2).
The
follow-up period ranged from 6 months to 4 years. During the follow-up, all the
patients had either symptoms unchanged (3 patients, 30%) or improved (7
patients, 70%). In 7 patients symptoms totally resolved. No manifestations of
recurrent retethering detected in any patient during the follow up period.
Table (3) shows the Pre and Postoperative Urodynamic and
Somatosensory Evoked Potential (SSEP) parameters. They were done six months
post operatively. There was statistically significant improvement in the
bladder function capacity, compliance and post voiding residual. Only two
patients still had hyperreflexic bladder. Data showed that SSEPs provide more
helpful information about the neurophysiological condition of the conus
medullaris during the follow-up period after detethering. One patient didn’t
improve from leg weakness after surgery and had equinovarus deformity. But SSEP
response to untethering showed no significant improvement (P=0.56) as shown in
urodynamic.
DISCUSSION
Knowledge
of the normal embryology allows better understanding of spinal dysraphism
defects and the anatomical relationship seen on diagnostic studies. The skin
lesions associated with spinal abnormalities include hypertrichosis, dimples,
lipoma, angioma and naevi12. In this study, about 9 cases (90%) had
a cutaneous lesion. But only seven patients (70%) had clear skin cutaneous
lesions lead to a clinical suspicion of spinal dysraphism3. This
situation clarifies why mean age group is relatively higher in tight filum
terminal group rather than lipomyelomeningocele dermal sinus. Nevertheless, patients without apparent
neurological deficits or clear skin lesion may have abnormal electrophysiologic
or urodynamic studies13. This alternate is helpful in early
detection of cases which mandate further MRI study14.
Final
diagnosis of spinal dysraphism depends mainly on MRI. Hall et al15
also found MRI to be the procedure of choice to diagnose a tethered cord and
had an excellent correlation between MRI and the surgical findings. Raghavan et al.16 concluded that
MRI was very useful in visualizing the conus medullaris, assessing the
thickness of the filum terminale, and identifying traction lesions in a patient
clinically suspected of having tethered cord syndrome (TCS). Associated bony
dysraphism was easily evaluated17.
In the
tethered cord syndrome, the distal lumbar spinal cord is fixed at 2 points,
first at the site of tethering, and second at the nerve roots exits. During
extension, flexion or the abdominal Valsalva maneuver there is a lack of motion
and stretching of the cord and roots, which can lead to ischemia and an
anaerobic metabolism10. The clinical spectrum of TCS includes pain,
sensorimotor defects of the lower extremities, bladder and bowel dysfunction,
and leg atrophy and scoliosis. In this study, 6 (60%) cases had initial presenting
symptoms of neurologic and urologic symptoms due to tethering of the spinal
cord and 5/6 (83%) had sphincter troubles3. Because the
inter-neuronal axon connections require an aerobic metabolism, they are the
first affected and clinically this leads to urinary incontinence and a
decreased skeletal muscle reflex. In contrast, the long neuronal tracts
involving muscular movement are less susceptible to hypoxic injury and, hence,
the findings of lower limb weakness with associated hyperreflexia and an upward
Babinski reflex are delayed manifestations of neurological impairment18.
Loss of the sacral reflex arc and the development of neurogenic detrusor
over-activity are the earliest alterations that can be detected by physical and
urodynamic examinations. In this study, patients with bladder hyperreflexia
responded favorably to TC release (3/5 60%). (1) Neurogenic detrusor
overactivity bladder had the highest response rate for surgery with average 59%
- 72%10, 19, 20.
Constipation
is not frequently referred in the literatures as associated with tethered cord.
In this series, constipation represented 20% of cases. Rosen et al., noted that
only 9% of children with spinal cord abnormalities had intractable constipation
but TC was the most common association21. In another study,
constipation was found in 42% of patients, decreased to 25% after surgery10.
All the
patients, except one, had normal motor, sensory, and reflex functions in their
lower extremities. Back pain (30%), leg pain (10%), and distal foot weakness
and foot deformities (10%) were found in the study. Limb deformities may be
associated with abnormal electrophysiology within the spinal cord22
or abnormal innervations of the lower limb13,20, and therefore, may
be unlikely to be responsive to untethering13,14. Sequential SSEPs
through stimulation of the posterior tibia1 nerve, although difficult to
perform in infants, can give a better account of the clinical evolution, based
on changes in cortical and lumbar amplitudes and latencies23. Serial
SSEP with peroneal or posterior tibial stimulation may reflect deterioration
secondary to retethering on follow up. Static rather than deterioration was
noticed denoting success untethering8,24.
Although,
we have relatively high incidence of post-operative CSF leakage 50% and one
child with skin infection, up to 20% of patients who undergo untethering
procedures experience local complications1. Other reports showed
about 3.9-5% of patients manifested neurological deterioration14, 25.
Controversy
persists regarding surgery in asymptomatic with TCS. In a given patient, it may
be difficult to decide whether there is a likelihood of progression or
development of neurological symptoms. Most patients are referred for surgery
only after onset or progression of symptoms18. In this study, 70% of
cases improved and 30% were stationary in their symptoms. Many surgeons
recommended that if surgery is delayed until the onset of neurological
deficits, there is a definite risk of incomplete neurological recovery6,9,10,17,23,24.
Furthermore, even if there is neurological recovery after surgery, the
orthopedic deformities of the feet which may have developed in the meantime are
permanent17.
In conclusion; Occult
spinal dysraphism and the tethered cord syndrome present innumerable challenges
to the neurosurgeon and neurologist. Early recognition of symptoms and signs
due to tethering of the spinal cord especially cutaneous stigmata should raise
suspicion for the disease. Advances in diagnostic imaging, urodynamic study,
neurophysiological monitoring, and early surgical release of the tethering
element have resulted in proper management of these clinical disorders. Follow
up is important to record improvement and tracing occasionally recurrent
retethering which mandate re-surgery.
[Disclosure: Authors report no
conflict of interest]
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