|Year : 2006 | Volume
| Issue : 3 | Page : 5-9
Split cord malformations
Department of Neurosurgery, Manipal Institute for Neurological Disorders (MIND), Bangalore, India
N K Venkataramana
Department of Neurosurgery, Manipal Institute for Neurological Disorders, Airport Road,Bangalore - 560 017
Split cord malformations (SCM) are increasingly being recognized as one of the causes of tethered cord syndrome. Renaming them as SCMs has reduced the conflict in terminology, though the pathogenesis of these complex anomalies still remains controversial. The diagnosis has become easy and certain with the advent of magnetic resonance imaging (MRI). It is necessary to screen the entire spine in order to recognize all the associated anomalies and to plan the management strategies. Aim: To study the role of prophylactic surgery in patients with SCM. Settings and Design: Retrospective clinical analysis. Methods and Material: In a series of 217 children treated with spinal dysraphism from 1994 to 2004 at Manipal Institute for Neurological disorders (MIND), 38 had SCMs and the clinical presentation and surgical outcome was retrospectively analyzed.
Statistical analysis used Results: 34 children had isolated SCM, four children had other complex congenital anomalies. 23 children [type 1-18 (47%) and type 2-20 (53%)] were operated prophylactically. They maintained neurological stability after surgery. Among the children with pre-existing neurological deficits, stability was achieved in all and significant improvement in only 8%. Outcome was better in isolated SCM in compression to complex ones. Conclusion: We recommend surgery before the onset of neurological deficits. Surgical results are excellent with good microsurgical technique
Keywords: split cord malformations; diastematomyelia; tethered cord syndrome; prophylactic surgery.
|How to cite this article:|
Venkataramana N K. Split cord malformations. J Pediatr Neurosci 2006;1:5-9
Split cord malformations (SCM) are rare and complex conditions. In the recent years magnetic resonance imaging (MRI) has renewed the interest in diagnosis, basic, understanding and management of these anomalies., Now it has become an established cause of 'Tethered cord syndrome'. Several terminologies were in vogue in literature like 'Diastematomyelia' (Olivier) 'Diplomyelia' (Bruce) with poor distinction. Pang et al. have proposed unified theory and recoined them as 'Split cord malformations'. ,,, The clinical records were analyzed to evaluate the clinical features and its correlation to the surgical outcome.
Most widely accepted theory about embryogenesis of this complex malformation was originally proposed by Bremer and subsequently modified by Pang et al., as 'Unified theory of embryogenesis.' The basic error appears to be development and persistence of 'Accessory Neurenteric Canal' (ANC). In the early weeks of gestation Primitive Neurenteric Canal temporarily connects the yolk sac (Endoderm) with amniotic cavity (Ectoderm). Simultaneously an ANC appears and its persistence will result in a variety of SCMs.,, The persistence of anterior end of this canal will result in intestinal malformations, posterior end, in cutaneous malformations like angiomas, hypertrichosis, dermal sinus or dermoid. Where as the persistence of intermediate part causes the split in the notocord and the neural placode. Division of notocord then leads to formation of hemiverterbrae, bifid, hypertrophic, hyperplastic vertebrae or fusion of vertebral bodies or posterior elements. The division of placode later on drives the formation of two hemicords.
If the mesenchyme surrounding the ANC contain precursor meningeal cells which results in the formation of dura and bony spur within, leading to SCM type I. If meningeal cells are not incorporated then it is not involved in the formation of dural sac. And once ANC disappears it will be transformed into intradural fibrous band situated between the two hemicords, thus constituting SCM type II. The persistence of ANC could occasionally interfere with neurulation process leading to the formation of meningocele or meningomyelocele, compounding these malformations further.,
| » Methods and Material|| |
In a series of 217 children treated with spinal dysraphism from 1994 to 2004 at Manipal Institute for Neurological disorders (MIND) 38 had SCMs [Table - 1]. These medical records were retrospectively analyzed. The clinical features were analyzed and correlated to the surgical outcome.
After a detailed clinical examination MRI was performed under sedation to confirm the diagnosis. Majority underwent screening of entire spine. Computed tomography (CT) was done in addition in ten children. All the children underwent surgery after adequate preanesthetic evaluation. Surgery was considered prophylactic in 23 (61%) as there was no neurological deficits. These children were followed for a period of 5 years. The surgical outcome was compared between the prophylactic and symptomatic group and also correlated with clinical presentation.
| » Surgical technique|| |
The child is positioned in prone with underlying supports. Midline skin incision is made extending above and below the level of the lesion. Subcutaneous tissue and the paraspinal muscles were carefully separated. Usually, the widened interpedicular distance or thick posterior elements will assist as a landmark to locate the spinal segments involved. One should be careful about bony defects and the scoliotic curves during dissection. It is preferable to expose the normal laminae one level above and below. The laminae can be hyperplastic or fused. Laminectomy is started at the normal level and continued on both sides close to the pedicles in an encircling fashion, protecting the dura and presenting facet joints. The ligaments are gently removed. The central bony spur with its attachment to the lamina is isolated. The two dural tubes are identified and protected. The bony spur is nibbled gradually till its attachment after careful and adequate separation from dura. There can be profuse bleeding from venous plexuses or occasionally from an arterial source. The dura is then opened in the midline at normal level extending down elliptically on either side of the sleeve of the spur joining in the midline caudally. It is important to open the dura medially as close to the split as possible to prevent stenosis. The arachnoid is also opened. The dural sleeve over the spur is then completely excised. The cords are inspected anteriorly and posteriorly and all the surrounding arachnoidal and fibrous bands are removed. After securing hemostasis, the dura is closed posteriorly in the midline converting into a single dural tube. The anterior defect of dura need not be closed. If the filum cannot be accessed in the same field a separate exposure is made at L5-S1 level to cut the filum [Figure - 1] and [Figure - 2].
In type-II Malformations, posterior bony elements almost look normal and hence a marker will be necessary. After laminectomy or laminotomy of the required levels the dura is opened in midline. The hemicords are inspected under magnification for the fibrous bands. The fibrous band is usually located ventrally between the hemicords. The band is released from its dural attachment. Other fibrous bands if present should be released. The filum is untethered and the dura is closed in the midline.
In complex malformations, the other associated anomalies are also dealt with appropriately in the same sitting.
| » Results|| |
Thirty-eight children were diagnosed to have SCN out of 217 patients with congenital spinal anomalies treated at our center. This constitutes 17.5% of the various spinal anomalies seen in children. Age ranges from 3 months to 18 years, with a slight female preponderance (male - 36% and female - 64%). 28 (74%) were diagnosed by cutaneous markers like hypertrichosis, angioma and nevi in the order of preference. Hypertrichosis was a hallmark except in two (5.3%). Fifteen (39%) presented with neurological deficits. The MRI revealed type I anomaly in 18 (47%) and type II anomaly in 20 (53%). Twenty-three children were operated prophylactically. All of them maintained stable neurological state in the follow-up period. Among the children with neurological deficits, only three (8%) improved, while in the remaining, deterioration was arrested. Four (11%) children had complex anomalies and they did not show any neurological recovery. Among the symptomatic, pain improved in all and scoliosis got stabilized. There was no mortality. Transient CSF leak was seen in four (11%) and superficial wound infection in two (5%) [Table - 1].
| » Discussion|| |
Split cord malformations can be defined as a form of occult spinal dysraphism, in which any part or entire spinal cord, cauda equina, and filum terminale are divided into two lateral parts by the dorsal - ventral spur. The original description diastematomyelia denotes splitting of the cord with a bony spur extradurally. Spinal roots arise from the lateral aspect of hemicords with no medial roots. Diplomyelia is supposed to represent true hemicords therefore harbored in a single dural tube, with medial roots from each hemicord. While the others believe that diplomyelia is extremely a rare condition, associated with split of ventral and dorsal horns. Pang introduced the term 'Split Cord Malformation.'
SCM type I
Constitutes 40-50% of SCM.,, Widening of interpedicular distances and hyperplastic laminae are usually associated., Dural sac is always double, with division of spinal canal and cords by extradural bony or cartilaginous spur. The spur can be antero-posterior usually attached to posterior surface of the vertebral body. Rarely it can have dorsal attachment to the spine. The spur can divide the canal into two symmetrical halves or can be slanting in the axial plane dividing the canal asymmetrically. In such situations one of the hemicords can be hypoplastic. Harwood-Nash et al. have reported such asymmetry in 50%. In majority spur is located at lumbar and less frequently in lower thoracic, cervical and upper thoracic regions, respectively. Double level spurs have also been reported occasionally. We have encountered two level spurs in one child at lumbar and lower thoracic regions. The separation of the cords can extend over several segments before they reunite caudally and the spur is located in the crouch [Figure - 3] and [Figure - 4].
SCM type II
Accounts to 50-60% of SCMs?.,, In this anomaly dural sac is single, one spinal canal and two almost equal and symmetrical hemicords between which may be an anterio posterior fibrous band tethering the cords to the dura. Recently, the importance of these fibrous bands as the cause of symptomatic tethering has been highlighted by several authors.,,,,
| » Compound or composite SCM|| |
Usually are associated with open dysraphic states. Various forms of split cords can frequently coexist in children with dysraphism, the so-called Composite lesions. It could be type I or II or may be a combination at same or at different levels. Occasionally the division of the cord is not so clear but there may be double central canal, duplicated dorsal or ventral horns. Diffuse structural disorganization and dysgenesis is also known. Occasionally the two hemicords are partially bridged known as Horse-shoe cord. Composite lesions are associated with other forms of occult dysraphism, such as lipoma, dermoid or epidermoid, sinus tract or a teratoma.-,, Overall outcome is good in isolated SCMs, in comparison to complex anomalies., We had four children with complex associated anomalies. One should carefully evaluate these children to exclude poly malformation syndrome. Several bony and visceral anomalies are known to co-exist?,, [Table - 1] and [Table - 2].
Although majority are diagnosed in infancy, symptoms can manifest at any age. In our series majority became symptomatic by second decade as reported in the literature. The neurological symptoms can vary from pain, bowel and bladder dysfunction, motor or sensory deficits. Spinal deformity, asymmetry of the limbs, gait disturbance and trophic ulcers are the other associates. In older children pain (lumbago or lumbosciatic) and paraesthesias are more common.,, The symptoms can be precipitated by trivial fall in an otherwise asymptomatic child. Prenatal diagnosis is now possible. One should search for anomaly of spinal alignment, midline cutaneous anomaly, enlargement of spinal canal and echoic mass in the spinal canal (spur) in prenatal ultrasound examination. Prenatal diagnosis was possible in two children [Figure - 5].
Plain X-ray, CT scan, CT myelography, and MRI are the imaging modalities used to diagnose this anomaly. The radiological abnormalities have been vividly explained by Neuhauser et al. Although some of the abnormalities can be recognized on plain X-ray, high resolution CT scan is sometimes necessary in identifying the spur. MRI has become the procedure of choice, to demonstrate spinal cord, dural sac, the spur, location of filum terminale and other associated abnormalities. Filum terminale can be short and thick in 40%. Spinal cord can be completely split in some with two separate filums. Hydrosyringomyelia, dermal sinus, dermoid, epidermoid or lipoma can be associated. The CT and MRI can be complimentary in increasing the diagnostic accuracy. Urodynamics forms an important aspect of evaluation to assess the bladder function,,,,, [Figure - 6] and [Figure - 7].
| » Surgery|| |
Neurological deterioration is believed to result from the tethering phenomena. The symptoms and their manifestation may vary depending on the type and associated anomalies. Since majority become symptomatic by second decade, and eventually deteriorate in their neurological function several authors recommend prophylactic surgery. On the other hand, Jamil et al. consider that the deficit is not always progressive and surgery can only be indicated in patients with progressive neurological deficits.,,,,,
The author feels that the prophylactic surgery is logical as the neurological deficits once occur are not completely reversible, on the other hand the children with no neurological deficits maintain steady neurological state postoperatively. The onset of neurological deficits seems to be early in type I malformation in comparison to type II. Although in the initial years, type II malformations were not operated without symptoms or signs, over the years of experience, we are convinced that surgery is beneficial soon after the diagnosis. The complex anomalies and neurologically compromised children demands appropriate clinical judgement in arriving at logical decisions for surgery. The ideal time of surgery is around 6 months of age when anaesthesia and blood loss is better tolerated.
In our series, all children who underwent surgery prophylactically had very good outcome. There was no postoperative deterioration and a stable neurological state was maintained. Symptoms like thinning of limb may not improve, if one of the hemicords is thinner and may be associated with neurological dysgenesis. Nonimprovement of deficits was attributed by Erickson to the myelodysplasia with congenital neuronal absence or dysgenesis.
| » Conclusion|| |
The SCMs are rare complex forms of occult dysraphism. In type I cord is anchored by an extra-dural bony spur and short, thick filum terminale. In type II tethering is caused by fibrous band, which anchors, hemicords to the anterior dura. The MRI is the choice of investigation, but high resolution CT can be complimentary. Hypertrichosis is the commonest marker to the clinical diagnosis. Surgery and detethering should be considered prophylactically after diagnosis and in all symptomatic children. Rational decisions are necessary in children who are neurologically compromised and harbor complex anomalies. In our experience, prophylactic surgery yielded good results and prevented subsequent neurological deterioration. Outcome is very good in children with isolated split cord malformation without associated complex malformations.
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[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4], [Figure - 5], [Figure - 6], [Figure - 7]
[Table - 1], [Table - 2]