Introduction to Split Cord Malformations

CHAPTER 1

Amol Raheja, Sanjeev A. Sreenivasan, and Ashok K. Mahapatra

Table of Contents

■ Introduction

■ Embryogenesis

■ Clinical Profile

■ Diagnostic Imaging and Radiological Workup

■ Principles of Management

CHAPTER
1

Introduction to Split Cord Malformations

Amol Raheja, Sanjeev A. Sreenivasan, and Ashok K. Mahapatra

Introduction

Over decades, the nomenclature for patients with double spinal cords have been changed from diplomyelia or diastematomyelia initially to the currently accepted split cord malformations (SCM), due to the implications of their disparate embryogenesis, dubiety in their terminology, and conflicting usage.²^,² Multiple initial hypotheses for the genesis of SCM included disorder of notochord genesis, germ layer segregation, or neurulation. However, the most widely accepted hypothesis is the Pang’s unified theory of embryogenesis, which proposes that a common ontogenetic error leads to double cord malformations vis à vis formation of adhesions between endoderm and ectoderm, ultimately culminating into an endomesenchymal tract surrounding persistent accessory neurenteric canal that bisects the developing notochord into duplicate hemineural plates.²^,² This modified state of developing hemineural plates and embryogenetic destiny of endomesenchymal tract constituents govern the final configuration of hemicords and nature of midline septum. This hypothesis also explains the high incidence of fore- and midgut anomalies as well as open myelodysplastic and cutaneous lesions associated with SCM.²^,² 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

Pang further subclassified SCM into type I and II, based on median septum characteristics and dural tube status surrounding the two hemicords.²^,² SCM type II consists of single dural tube housing two hemicords, which are separated by a fibrous median septum that is nonrigid. On the contrary, SCM type I houses each hemicord in its own dural tube, and they are separated by a rigid osseocartilaginous midline septum.²^,² All other associated tethering elements in SCM such as centromedian vascular structures, myelomeningocele manqué, and paramedian nerve roots do overlap between SCM types I and II; hence, there are no consistent differentiating criteria.²^,² 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 patients with SCM in a nutshell. A detailed discussion will be conducted separately in further chapters.

Embryogenesis

The key differentiating step between formation of SCM-I and SCM-II is the recruitment of meninx primitiva precursor cells during mesenchymal investment over endomesenchymal tract.² Pluripotent cells of endomesenchymal tract could develop into a variety of tissues, including 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.² Similarly, endodermal remnants may present as neurenteric cyst or intestinal duplication.²^,²

Only gold members can continue reading. Log In or Register to continue