Split Cord Malformations Type II

CHAPTER 5

Amol Raheja, Tarang K. Vora, and Ashok K. Mahapatra

Table of Contents

■ Introduction

■ Embryogenesis and Histopathology

■ Clinical Presentation

■ Diagnostic Imaging and Radiological Workup

■ Principles of Management

■ Conclusions

CHAPTER
5

Split Cord Malformations Type II

Amol Raheja, Tarang K. Vora, and Ashok K. Mahapatra

Introduction

Split cord malformation (SCM) is the currently acceptable nomenclature for any patient with double spinal cords. The unique morphology of SCM acquired by each patient depends on three embryogenetic fates of the endomesenchymal tract: (1) variable extent to which endomesenchymal tract persists; (2) the embryo’s ability to heal around endomesenchymal tract; and (3) the cumulative destiny of dislocated midline mesoderm and endoderm.2^,²

As per Pang’s classification, SCM is further subclassified into type I/II, based on median septum characteristics and dural tube status surrounding the two hemicords.²^,² SCM type I houses each hemicord in its own dural tube, which are separated by a rigid osseocartilaginous midline septum. On the contrary, SCM type II consists of a single dural tube housing two hemicords separated by a fibrous median septum, which is nonrigid²^,² (Fig. 5.1). This currently acceptable classification helps subdivide SCM cases preoperatively, based on the radiological imaging, and further plan their surgical management and risk assessment accordingly.²^,²^,² This chapter has been conceptualized to understand the embryogenesis, clinical presentation, diagnostic imaging, radiological workup, decision-making process, and surgical strategy in management of individuals with SCM type II.

Fig. 5.1 Radiographic imaging of a 20-year-old female presenting with progressive neurological deficits and neuropathic ulcers. Axial (a–d) and coronal (e) MRI of dorsolumbar spine demonstrating SCM type II, with two hemicords lying within the single dural tube (marked by arrow). There is no bony spur seen in the median septum separating and tethering the two hemicords.

Embryogenesis and Histopathology

In contrast to SCM type I, pathogenesis of type II malformation involves lack of precursor cells’ recruitment from meninx primitiva during the mesenchymal investment period over the abnormal fistula (accessory neurenteric canal), it is possibly attributable to the completion of endomesenchymal tract prior to the appearance of definite meninx primitiva (day 30).² Hence, the development of midline mesenchymal components will be much less complex in type II malformation, where only a thin fibrous septum is formed between the two hemicords. Moreover, the fibrous septum of type II SCM is anatomically located at the caudal extent of the split, and is usually oriented obliquely in such a fashion that its dural attachment is almost always caudal to its hemicords attachment.²^,²^,²^,² The explanation for this observation is that relatively more compliant endomesenchymal tract in SCM type II presumably renders the hemicords with slightly higher degree of freedom for vertical movement as compared to SCM type I. More permissive and pliable transfixation of the neural tube by the endomesenchymal tract in SCM type II probably also accounts for lower extent of “splitting” of the cord seen in SCM type II when compared to SCM type I.²^,²^,²^,² The fact that majority of type II SCM cases have intact overlying skin over the split cords implies that the cutaneous ectoderm closed the dorsal opening of fistulous neurenteric canal and formed intact skin in the early stage of its embryogenesis. However, the involvement of surface ectoderm by dorsal endomesenchymal tract can get manifested in the form of hypertrichosis, capillary hemangioma, etc.²^,²^,²^,² A more infrequent association of open myelomeningocele and SCM can be occasionally seen, although the exact embryogenetic mechanism accounting for such an association is not known.²^,²^,²^,²

Pluripotent cells from endomesenchymal tract could develop into multiple discrete tissues. Ersahin 2 demonstrated that pathological specimens from median septa of SCM patients reveal lymphoid tissue, blood vessels, dermoid cysts, tubular epithelia, muscle tissue, ganglion cells, fetal renal tissue and, rarely, teratomas in addition to osseocartilaginous tissue seen in SCM. The hypothesis for the presence of displaced neural crest cells in the median fibrous septum of SCM type II stems from the histological evidence of presence of ganglion cells, suggesting that the “extra” nerve roots in median septum are essentially the central processes of neural crest cells entrapped by the endomesenchymal tract.²^,² Intestinal duplication or neurenteric cyst, endodermal remnants of endomesenchymal tract, may be rarely associated with SCM type II.²^,² Persistence of ventral and dorsal endomesenchymal tract leads to differential association of dermoids, intestinal malrotation, and dermal sinus tract with SCM type II. The theory of ectoendodermal adhesion and endomesenchymal tract is further supported by the presence of variable degree of ectodermal, mesenchymal, and endodermal structures detected from the median septa.²^,²

Clinical Presentation

SCM is noticed in approximately 20% of children with neural tube defects.²^,²^,² Neurological deficits are proportionately distributed across both SCM types I and II. In a large series of 300 SCM patients by Mahapatra,² it was demonstrated that 60% of patients had cutaneous marker and 80% had scoliosis or lower limb deformities, which act as surrogate markers for underlying SCM. The most frequently associated cutaneous marker with SCM type II is hypertrichosis, with an incidence varying from 20 to 55%.²^,²^,²^,² Majority of SCMs are seen in lumbosacral region, followed by dorsal region, and only rare instances of cervical cord tethering by SCM type II has been reported in the literature. Therefore, a strong clinical suspicion is paramount in timely diagnosis of cervical SCMs, which if left untreated may lead to hand dysfunction apart from spastic legs.²