Long-Term Outcome for Patients With Split Cord Malformation

Mark R. Proctor, M.D., and R. Michael Scott, M.D, Department of Neurosurgery, Children's Hospital, Harvard Medical School, Boston, Massachusetts

Neurosurg Focus. 2001;10(1) 

In This Article

Abstract and Introduction

Object. Split cord malformations (SCMs) are relatively rare forms of occult spinal dysraphism (OSD) and tethered spinal cord syndrome. The majority of these cases present in early childhood, with neurocutaneous stigmata being an early presenting feature. Prophylactic detethering surgery is advocated by most neurosurgeons due to the risk of neurological deterioration over time caused by patient growth and activity. However, unlike other forms of OSD, the course of SCM progression after surgery is not well understood, and little has been published about long-term follow-up results. In this study the authors review the results obtained in 16 patients in whom the senior author performed surgery over a 13-year period (average length of follow up almost 8 years).
Methods. Presentation, surgical approach, and outcome are evaluated, and the long-term outcome of neurological status, pain, bowel/bladder disturbance, and spinal deformities are emphasized.
Conclusions. The primary conclusion is that patients with SCM generally tolerate surgery well and experience few complications. Neurological deterioration is rare except in cases in which retethering occurs, (two patients in this series). Although impaired bowel and bladder function was stabilized or improved and pain was reliably relieved post-operatively, preexisting vertebral column deformities usually progressed after surgery and, in most cases, required spinal fusion.

Split cord malformation is a form of closed neural tube defect in which the spinal cord is longitudinally split by a fibrous band or a bone spicule. This new nomenclature of SCM was introduced by Pang, et al.,[16,17] in 1992, to eliminate confusion created by the use of the terms diastematomyelia and diplomyelia. Diastematomyelia usually refers to a split cord in which the two halves are separated by a bone spicule and contained within separate dural sleeves. In contrast, the term diplomyelia is generally used to describe a condition of two hemicords within one dural sac, often with two complete sets of nerve roots, separated by a fibrous band. Unfortunately, inconsistencies in the use of these terms have created substantial confusion on this subject in the literature. Based on the detailed findings in 39 cases and review of embryological features, Pang, et al., proposed a common origin of both malformations: an adhesion between the ectoderm and endoderm leads to an endomesenchymal tract that bisects the spinal cord. If the tract also contains cells of the meninx primitiva, the resultant malformation would be SCM Type I, or diastematomyelia. Otherwise, the formation of a separate dural sleeve and bone septum does not occur, and the malformation is a SCM Type II, or diplomyelia.[17,20]

Both types of SCMs represent lesions that tether the spinal cord during growth and movement.[17] As with all TCSs, surgical intervention is usually indicated based on an expected natural history of disease progression in the absence of treatment.[9,22] In a previous review we examined the pre- and postoperative urinary function in patients with SCM by performing formal urodynamic studies.[20] It was found that although a minority of the patients with SCM presented with urological signs or symptoms, formal testing demonstrated occult urological abnormalities in 75% of the patients. These urinary abnormalities tended to stabilize or improve after surgical intervention. Unlike other forms of spinal tethering, little is known about the long-term surgery-related outcome of patients with SCM. In this series we examine the long-term outcome of patients with SCM who have undergone surgical detethering.