Split Cord Malformations Type I

CHAPTER 4

Shweta Kedia, Rajesh Meena, and Ashok K. Mahapatra

Table of Contents

■ Introduction

■ Anatomy and Classification

■ Inheritance

■ Clinical Presentation

CHAPTER
4

Split Cord Malformations Type I

Shweta Kedia, Rajesh Meena, and Ashok K. Mahapatra

Introduction

The first mention of split cord malformation (SCM) type I was made for a 1,800-year-old cadaver with a butterfly-shaped vertebra at the thoracolumbar junction, which had a bony spur that divided the spinal canal into two.²^–² However, Ollivier² has been rightly credited to have described diastematomyelia in 1837. The origin of this term is Greek: diastema synonym of cleft, and myelos for cord. In 1892, almost 55 years later, Hertwig used the term “diastematomyelia” for split spinal cord, each having an individual dural sac divided by a bony spur in the midline with a single set of dorsal as well as ventral nerve roots.²

SCM is considered a presentation of occult spinal dysraphism. It is present mostly in the pediatric population, but there are few cases reported in adults as well.²^,² The literature suggests the incidence rate of 2 to 4 per 1,000 live births, but it may be misleading,² as it has a complex presentation and may not always be diagnosed correctly.²^–² The female to male ratio is 1.5–1.3:1 and is suggestive of female preponderance.²^–² The classical description of SCM type I is when the spinal cord is divided by a bony spur into two hemicords in the sagittal plane, each having their own central canal with dorsal and anterior horns and usually associated with a low-lying conus with thick or fatty filum.² These patients have varied degree of urological, musculoskeletal, and sensory system involvement with subtle or obvious cutaneous markers.

In this chapter, we shall discuss the anatomy, imaging, clinical presentation, management, and outcome of SCM type I. Embryogenesis has been discussed in chapter 2 in the book.

Anatomy and Classification

SCM has been commonly classified into two types: type I with an intervening bony or fibrocartilaginous spur dividing the neural tube into two with separate dural sheath, and type II, where there is a fibrous septum between two hemicords and a single dural sheath which encloses the split cord.²

Not all SCMs fit these descriptions precisely, and there has been several attempts to reclassify the SCM for a better anatomic understanding.² In their paper, Mahapatra et al have attempted to classify the SCM I into four subtypes. They studied the location and extent of the bone spur bifurcating the spinal cord and based on that they explained each subtype in surgical context.²

The bony spur extends in the anteroposterior direction and usually divides the canal with the cord into two almost equal halves, or at times the spur runs oblique in the axial plane, and this divides the spinal cord into asymmetrical halves, one of which is normal and the other abnormal, hypoplastic. The embryogenesis also supports this new classification. Type Ia SCM in this classification can be because of the endomesenchymal tract disappearing variably at the upper and lower portions after splitting the notochord and the neural plate. Primitive meninx induces bone formation in the center of the split. Likewise, in Type Ib, the endomesenchymal tract disappears caudally, while in Type Ic the endomesenchymal tract remained persistent at the lower pole. Type Id has wide, tight split with the bone septum straddling the bifurcation, and here the endomesenchymal tract remains persistent throughout. The MRI and the axial CT scan findings often correlate with this classification and help surgeons anticipate the intraoperative findings.²

The spur is most commonly observed in the lumbar area, but also has been reportedly observed in the cervical, lower thoracic, upper thoracic, and sacrum in decreasing order of frequency.2

It is not also unusual to find that the two hemicords continue as two different fila, but normally at the end of the spur, they join together to continue as a single filum. In the presence of two separate fila, one should think of composite SCMs and go through the imaging carefully.²^–²

Inheritance

Most of the times, SCMs appear in isolation and does not show a familial pattern. Only four cases mentioned in the literature showed a hereditary pattern and all of them were in females.² No reports mention an affected parent and a child. However, again, these numbers may be misleading because of the rarity of reporting. Some authors did suggest an X-linked inheritance in a dominant fashion.

Unlike, the often-quoted risk incidence of 4% of having an affected child for parents with spinal dysraphism, it cannot be said for a parent with SCM.²

Clinical Presentation

The usual presentation is at the age of 2 to 4 years, with a second peak at adolescence at the time of rapid growth. With the advancement in the imaging, the age at diagnosis can range from the prenatal period to adulthood.²^,²^–²

The presenting symptoms can be divided into cutaneous stigmata, deformities in the lower limb/ musculoskeletal system, and neurological deficits (Box 4.1).

Box 4.1 List of clinical signs and symptomatology

Cutaneous findings

•Hypertrichosis.

•Capillary hemangioma.

•Hyperpigmentation.

•Dimple.

•Subcutaneous lipoma.

Orthopedic deformities

•Kyphoscoliosis.

•Unilateral lower limb atrophy.

•Pes echinovarus/cavus/valgus/calcaneovarus.

•Neurotrophic ulcers in foot.

•Spontaneous amputation of toes.

Neurological findings

•Low back pain.

•Paraparesis/paraplegia, monoparesis with or without bladder and bowel involvement.

Hypertrichosis is the most common skin manifestation.²^–² Pang² in his paper on clinical presentation of split cord suggested that these cutaneous manifestations may result from minor aberrations occurring during the surface ectoderm development. It is not so commonly present in patients with myelomeningocele (MMC), as these aberrations are overshadowed by chaotic changes occurring in the surface ectoderm, which are also occasioned by the unneurulated neural plate. This theory has been supported by other authors as well.²^,²

All the structural deformities that occur in patients with SCM type I makes it surgically challenging. Literature states that scoliosis may be seen in almost 30 to 60% of patients with SCM.²^,² Also, conversely, 5% of patients with congenital scoliosis may have underlying SCM.²^,²^–² Higher the age of the child, more are the chances of scoliotic deformity (Fig. 4.1).

Fig. 4.1 (a–d) Patient presented with kyphoscoliosis. On investigation, he is found to have SCM type I.

It has been observed that the presenting complaint of adults with SCM is usually back pain and sciatica, as a part of manifestation of tethered cord.²^,² Occasionally, skin, musculoskeletal, or neurological abnormalities may also be present since childhood but were ignored.²^,²^–² Usually, trauma or strenuous exercise may lead to the precipitation of symptoms.² SCMs have been shown to be associated with the anomalies listed in Box 4.2.