Dattaraj P. Sawarkar, Deepak K. Gupta, and Ashok K. Mahapatra

Introduction

Occult spinal dysraphism2 is not an uncommon clinical entity in neurosurgical practice. Split cord malformation (SCM) is a rare form of spinal dyraphism characterized by a split along the midline of the cord, dividing it into two symmetric or asymmetric entities housed in same or separate dural tubes. SCMs represent up to 5% of the outpatient pediatric population with congenital spinal anomalies. Most of the patients are children and they present to their physician in infancy or early childhood. Age groups commonly presenting with these disorders are 4 to 7 years and 12 to 15 years;² the latter being a result of the growth spurt around puberty, which unmasks certain clinical features. Presence of neurocutaneous markers is a hallmark sign on first clinical examination. SCMs are congenital disorders where there is division of the spinal cord into two halves by a bony or fibrous spur. Cohen and Sledge² described diastematomyelia as a cleft or split within the spinal cord. Diplomyelia, coined by von Recklinghausen, is the presence of a separate cord-like structure dorsal or ventral to the original cord. Dimyelia is the presence of two true separated spinal cords within two distinct dural sacs. However, many of these terms were utilized interchangeably in the literature.

Over the years, various classifications have been described in the literature for SCMs.

Pang’s Classification

The unified theory of embryogenesis was first described by Pang et al,^2,2 classifying the SCMs in two types:

1.Type I SCM: It comprises two dural sacs separated in the midline by a bony spur. There is fusion of the lamina to the adjacent levels, and these laminae are often hypertrophic. CT scan examination reveals a bony spur. Type I SCM is usually characterized by presence of spina bifida defect and fusion of adjacent segments. These are most commonly located in the lumbar region (Fig. 3.1 and Fig. 3.2).

2.Type II SCM: It comprises a single dural sac encasing two hemicords. These are tethered to the dura via a fibrous band. MRI reveals two separate hemicords within a single subarachnoid space. Presence of fibrous strand can be demonstrated on a high-resolution MR. This may be located anywhere along the neuraxis.

Composite Split Cord Malformations

Some patients may have same or both types of SCMs at different levels with normal cord in between. This form of complex dysraphism is called composite SCM. Type I SCM has two hemicords housed in separate dural sheaths with an intervening bony spur, and type II SCM has two hemicords housed in a single dural tube with an intervening fibrous median septum (Fig. 3.3). The embryogenesis of such composite SCMs can be explained by the multiple neurenteric canal theory. There can be multiple separate foci of ectoendodermal adhesions and endomesenchymal tracts during the embryogenesis, leading to the development of composite SCMs with an intervening normal cord. This unique presentation of composite SCMs was noted by Ailawadhi and Mahapatra² in a patient having three posterior bony spurs and one fibrous spur at different levels. Similarly, Singh et al² reported a patient with long-segment type I SCM and type II SCM at the lower levels. The frequency of composite type SCM has been reported to be less than 1% by Harwood–Nash and McHugh.²

Location of Spur

SCMs can also be categorized according to location of spur. It can either be:

Chandra et al2 pointed out the presence of dorsally situated spur in 1999.

Completeness of Spur

Classification depending upon completeness of spur:

Anatomical-pathological modifications to Pang’s classification for type III SCMs were described by Alzhrani et al.2 They subdivided type III multilevel SCMs into the following: type IIIA: Bony spur at multiple levels, type IIIB: Fibrous septum at multiple levels, and type IIIC: Mixed fibrous and bony spur at multiple levels or with associated anomalies.

SCMs Associated with Other Spinal/Cranial Dysraphisms

•Spur alone.

•Spur with spinal dysraphisms like myelomenigocele (MMC)/myelocystocele/syringomyelia/lipoma/dermoid.

•Spur with cranial malformations like hydrocephalus (HCP)/Chiari/craniosynostosis (Fig. 3.4).

Spinal dysraphisms are congenital malformations affecting the spinal cord and vertebral bodies heterogeneously. These malformations can be simple or complex. Contiguous, solitary malformations are termed simple, whereas multiple malformations occurring in combination or in a noncontiguous manner with other organ anomalies are termed complex.

Open form of spinal dysraphisms can present incongruously with SCMs. MMCs have been reported in up to 41% of all SCMs.² Clearly, both open and closed forms of spinal dysraphisms can occur together. MMC was reported in 17.4% of SCM patients by Ozturk et al.² In their series of 33 patients with MMC, Higashida et al² noted three patients (9%) with SCM.

Chiari malformation, HCP, and syrinx are other frequent associations in patients with SCM and
MMC,^2,2 complicating the management of these disorders. Usually patients with SCM do not show association with Chiari malformation, but in patients with both SCM and MMC, it is a common occurrence.² HCP and syrinx also have been noted to be more common in patients with SCM associated with MMC than in those with pure SCM.^2,2 Myeloschisis associated with SCM has also been reported by Akiyama et al² and Yamanaka et al.² A case of lumbar SCM with lateral hemimyelomeningocele and associated Chiari II malformation was noted by Rowley and Johnson.²

Myelocystocele can also present with SCM. A 4-month-old girl with diastematomyelia, terminal myelocystocele arising from one hemicord, ectopic right kidney, Chiari I malformation, and partial sacral agenesis was reported by Parmar et al.2 A complex spinal dysraphism with two different level SCMs along with nonterminal myelocystocele, bifid fatty filum, coccygeal dermal sinus, and HCP was reported by Khandelwal et al.² A series of 17 and 8 cases of myelocystoceles were noted by Gupta and Mahapatra² and Jaiswal and Mahapatra,² respectively. Other organ abnormalities such as OEIS complex which include omphalocele (O), exstrophy of bladder (E), imperforate anus (I), and spinal abnormalities (S) are a common occurrence in patients with myelocystocele.²

A case of HCP, Chiari malformation, syringohydromyelia, SCM, dermal sinus tract, lumbosacral myelomeningocele, and tethered cord was noted by Emmez et al.² A 5-year-old boy with tethered cord, diastometamyelia, spinal dysraphism, terminal lipoma, spinal epidermoid, and dermal sinus tract was reported by Avcu et al.² Similarly, a child with a type I SCM associated with hemivertebrae, lipomyelomeningoceles in each hemicord of the SCM, a terminal myelocystocele, and concurrent segmental meningocele was reported by Solanki et al.² Two cases of SCM with intraspinal teratoma were reported by Maiti et al,² of which one was extradural within meningocele and other intramedullary.

Spur with Intracranial or Extracranial Malformations

•Spur with extracranial malformations (like dextrocadia/renal/gastrointestinal tract [GIT]/lung).

•Spur with intracranial malformations.

Other organ system malformations like genitourinary, cardiac, renal, etc. are frequently associated with spinal dyraphisms. Cases of multiple spinal dysraphic states with situs inversus or dextrocardia have been reported by Dwarakanath et al2 and Tubbs et al.² A complex form of SCMs associated with teratoma, extending into the mediastinum, was noted by Naik et al.² A 1-day-old male neonate with multiple right-sided anomalies, hypoplastic right face, decreased movement of the right upper limb with absent right cervical hemivertebrae, right cervical lipomyelomeningocele, and cervical diplomyelia with right hemicord terminating in a blind pouch was reported by Shieh and Lam.² Sacral hypoplasia and agenesis of right kidney was reported by Higashida et al² in one of their patients with MMC along with SCM.

A classification system should be relevant in terms of its embryology and clinical finding as well as help in planning management, deciding type of surgery, and helping in deciding long-term outcome.

New Proposal for Type I Split Cord Malformation by Mahapatra and Gupta^2,2

Pang’s unified theory of embryogenesis is well-accepted.² The theory states all SCMs to be a result of an error in the formation of the accessory neurenteric canal connecting the amnion and the yolk sac. This tract is invested with mesenchyme to form an endomesenchymal tract, splitting the neural plate and the notochord. All types of SCMs cannot be explained by this hypothesis.

To address this shortcoming, a new classification, based on intraoperative findings of spur level and its relation to cord, was put forth by Mahapatra and Gupta.^2,2 Their proposed subclassification of SCM type I is detailed below (Fig. 3.5):

Related posts:

Introduction to Split Cord Malformations Adult Split Cord Malformations Split Cord Malformations Type I Anesthesia for Neural Tube Defects Protocol for Management of Split Cord Malformations Composite Split Cord Malformations or Multisite Split Cord Malformations

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