Prophylactic Surgery in Split Cord Malformations

CHAPTER 11

Vivek Tandon, Skanda Moorthy, and Ashok K. Mahapatra

Table of Contents

■ Introduction

■ Clinical Presentation

■ Investigations

■ Treatment

■ Outcome

CHAPTER
11

Prophylactic Surgery in 11 Split Cord Malformations

Vivek Tandon, Skanda Moorthy, and Ashok K. Mahapatra

Introduction

Split cord malformations (SCMs) are a rare type of spinal dysraphism, and they are usually associated with low-lying tethered cords. SCMs constitute about one-third of spinal dysraphisms.2 Type I SCM has two hemicords in two separate dural sacs split by a bony spur present over variable spinal segments, and Type II has both the hemicords in the same dural sac and are split by a membranous septum. Type I SCMs have four subtypes, depending upon the location of the bony spur.² The most common location of SCM is dorsal and lumbar spine, and rarely can they be encountered in cervical or sacral areas.² In a newborn, conus ends at L3 level and as the child grows due to disproportionate growth of cord and vertebral segments, there is ascent of the cord till its final adult level of L1. SCM and low-lying tethered cord may be linked with a variety of other anomalies like conus lipoma, myelomeningocele, lipomeningomyelocele, dermal sinus tract, or meningocele.

As children with these malformations may be completely asymptomatic, controversy exists regarding prophylactic surgery in these patients. Low-lying cord can often be associated with scoliosis both congenital as well as secondary to weakness of paraspinous muscles. Prophylactic detethering before scoliosis correction is a preferred option in case of a low-lying cord.²^–² Prophylactic detethering increases the mobility of the cord inside the vertebral column; hence, decreasing the chances of damage during corrective surgery. However, there are opinions against the same on the basis that prophylactic surgery does not improve the neurological status. In contrast, it may cause deterioration, and is also associated with other neurosurgical complications like cerebrospinal fluid (CSF) leak, infection and neurological deterioration.²^,² Other factors against detethering include loss of posterior bony elements, which may contribute to further osseous defects and potential for regrowth of the spur.²^,² The option of prophylactic surgery with all its pros and cons should be discussed with the patients, and in this chapter we present our view, based on existing literature and our vast experience.

Clinical Presentation

Most of these patients present in early childhood either due to neurocutaneous stigmata or development of neurological deficits and deformity; however, there are incidents of patients presenting in the adulthood either due to back pain, neurological symptoms, or they may be completely asymptomatic. Associated tethering of the cord leads to limited cord movement and stretching while flexion and extension of back. This chronic stretching of the cord leads to ischemic insult to the cord and results in neurological symptoms. Various presenting clinical features include hypertrichosis in the back, dermal sinus, chronic back pain, numbness in the foot, weakness of lower limbs, bladder bowel incontinence, and scoliosis which may occur due to weakness of paraspinal muscles on either side.²^,²

Occasionally, physicians diagnose patients incidentally. These patients do not have neurological symptoms but are diagnosed due to presence of cutaneous stigmata, scoliosis, or radiological screening for any other cause.

Investigations

MRI is the investigative modality of choice; contrast should be used when a dermoid or teratoma is suspected on initial imaging. On MRI imaging, presence of two hemicords separated by a bony septum in two separate dural sheaths is diagnostic of Type I SCM, while a membranous septa separating the two hemicords in a single dural sheath is suggestive of Type II SCM. In about 50% of the cases, they occur at L1–L3 levels, and in about 25%, they occur at D7–D12 levels; in the rest 25% cases, they may occur at a higher level. Associated findings include scoliosis or other anomalies like lipomyelomeningocele and dermal sinus tract. Normal filum terminale is less than 2 mm thick. A thick fatty filum with lower than usual cord ending level (below L2) is a common finding in these cases (Fig. 11.1).