Complex Split Cord Malformations

As per this classification, all SCMs belong to the complex dysraphic states. However, in clinical practice, we do come across patients with SCMs along with other dysraphism, open or closed. The best way to describe them would be to refer to them as “complex spina bifida.” After a thorough literature search, we could find the term “complex spina bifida” first used by Raj Kumar et al in their paper on SCM with meningomyeloceles (MMC).²^,² He preferred to classify them as a separate entity to understand their embryology and clinical implications better, and proposed a revised classification over that of Pang’s as type I SCM with MMC and type II with MMC.²

Since then, the term “complex spinal dysraphism” have been used by several authors to illustrate the presence of multi- or same level, similar or different forms of spinal dysraphism, with or without hydrocephalus or syrinx, presenting in single individuals.²^–² This definition is controversial and may extend to include anything that is beyond the definition of isolated spinal dysraphism.

Mahapatra et al made an attempt to classify these complex dysraphisms into five broad categories based on literature citations.²

The common complex SCM encountered in clinical practice are as follows:

•Complex spinal dysraphism.

•Multicomponent spinal dysraphisms, consisting variable combinations of myelomeningocele, SCMs, lipoma, neurenteric cyst, dermoid, etc.

•Multilevel spinal dysraphisms like SCMs.

•Complex lipoma.

•Spinal dysraphisms with Arnold–Chiari malformation with or without associated hydrocephalus and syringomyelia.

•Spinal dysraphisms associated with other organ system malformations.

Embryogenesis

Complex spinal dysraphism occurs due to the disorders occurring in early embryonic stage (2–6 weeks). This stage involves complex changes in the cellular arrangements in the embryo and consists of gastrulation (weeks 2–3), primary neurulation (week 3), and secondary neurulation (week 3–4) and then goes through a multistep process.2^,² Any of the two stages with the gastrulation stage may be involved in complex dysraphisms. When the formation of the endomesenchymal tract happens before 3 weeks, it gives rise to type II SCM. SCM type I occurs when the endomesenchymal tract formation takes place after 4 weeks of gestation. The presence of commonly associated spinal abnormalities such as dermal sinus tracts, spinal lipomas, dermoids, neurenteric cysts, and even a meningocele or myelomeningocele occurs if the abnormal fistula forms between day 21 and 30.²

This form of presentation of SCM, while defies the universal theory of embryogenesis as advocated by Pang, also opens up the discussion on missing links between gastrulation and neurulation.²^,² Despite the various embryological hypotheses that have been put forth to explain the etiology of different types of spinal dysraphism, the experimental evidence in support of the same is absent.²^,²^–² The discrete nature of the lesions in these cases do imply that there are multiple sites of embryogenetic error happening in different stages in a particular individual. So, in a patient with SCM with low-lying cord along with hydromyelia, spinal lipoma and MMC, varied embryological stages are being affected. Partial retrogressive differentiation along with failed terminal cord involution results in low-lying cord.² Abnormal dilatation of the central canal after neural tube closure causes hydromyelia.² When there is premature separation of ectoderm and neuroectoderm during neurulation, it results in spinal lipoma,² and MMC arises from failed neural-tube closure.

The overdistension theory has also been used to explain the extremely high occurrence of multiple neural tube defects in the same baby. Therefore, oversecretion of neural tube fluid leads to rupture of the closed neural tube, resulting in secondary neural tube defects.²

As per Gardner, rupture of this overexpanded neural tube beneath an intact cutaneous ectoderm results in the proteinaceous neural tube fluid infiltrating the mesoderm. This extraneous protein causes dislocation of cells and further injury occurs by yet unidentifiable substrates of mesodermal organs.

This would also explain the occurrence of composite SCM.

Each subtype of these complex forms of dysraphism have been well described in literature. A knowledge of all of these is important, so as not to get carried away by the more obvious anomaly and miss out on other hidden offending pathologies existing simultaneously. In order to discuss the complex dysraphism, we need to walk through the complete spectrum of its associations.

■ Multicomponent Complex Spinal Dysraphism

The first and foremost topic authors discuss is MMC, which is the most common concurrent finding with SCM. It is a classic example of a situation where both the closed and open forms of dysraphism coexist. Data on its incidence varies because of the lack of uniform reporting system, but almost 10 to 40% of the cases of SCM may present with MMC. They also frequently present along with Chiari malformation, hydrocephalus, and syrinx, which are not otherwise present in pure SCMs (Fig. 10.1).²^,²^–²
Akiyama et al² and Yamanaka et al² have both reported cases on SCM with myeloschisis on separate occasions. Higashida et al documented absence of right kidney and hypoplastic sacrum in one of their MMC patients with SCM. There is also mention of hemimyelomeningocele in the literature, although rare.²^–² It may also be associated with a neurenteric cyst (Fig. 10.2). Rowley and Johnson reported a case of lumbar SCMs where one cord failed to neurulate, resulting in hemimyelomeningocele and associated Chiari II malformation and other visceral and osseous anomalies.²

Fig. 10.1 (a–d) Type 1 SCM presenting with Chiari malformation and holocord syrinx is one of the classic example of complex dysraphism.

Fig. 10.2 Spinal dysraphism along with neurenteric cyst is another form of complex spinal dysraphism.

Myelocystocele has also been reported to coexist with SCM. Parmar et al first described terminal myelocystocele arising from one hemicord in a 4-month-old girl with SCM I.2 This patient also had ectopic right kidney, Chiari I malformation, and partial sacral agenesis. Solanki et al reported a 10-month-old child with a type I SCM associated with hemivertebrae, lipomyelomeningoceles in each hemicord of the SCM, and a terminal myelocystocele.² This child was operated for myelocystocele elsewhere and the rest of the tethering elements were not looked for. The occurrence of all of this in one individual patient would require involvement of gastrulation, primary, as well as secondary neurulation. There are reports of nonterminal myelocystocele as well along with composite SCM.²

There have been several reports on multiple forms of dysraphism present at different levels in one individual. Emmez et al enumerated seven congenital malformations consisting of hydrocephalus, Chiari malformation, syringohydromyelia, SCM, dermal sinus tract, lumbosacral MMC, and tethered cord.² Similarly, Avcu et al reported a 5-year-old boy presenting with six different forms of dysraphism.² Maiti et al reported two cases of complex SCM with intraspinal teratoma, one located intramedullary and the other extradural within meningocele.² Naik et al and Ugarte et al reported a complex spinal dysraphism with mediastinal teratoma in two separate occasions.²^,²

■ Multilevel Complex Spinal Dysraphism or Composite Split Cord Malformations (SCMs)

Moving away from the discussion of different spinal dysraphisms present in one patient to multilevel split in single individual with intervening normal cord, multiple neurenteric canal theory leading to two or more separate foci of ectoendodermal adhesions and endomesenchymal tracts can explain the embryology of composite SCM.

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