Terminal myelocystocele.

Terminal myelocystoceles constitute approximately 5% of skin-covered lumbosacral masses and are especially common in patients with cloacal exstrophy. Pathologically, terminal myelocystocele consists of (a) a skin-covered lumbosacral spina bifida (b) an arachnoid-lined meningocele that is directly continuous with the spinal subarachnoid space; and (c) a low-lying, hydromyelic spinal cord that traverses the meningocele and then expands into a large terminal cyst. The terminal cyst bulges into the extraarachnoid compartment caudal to the meningocele and forms a distal sac that does not communicate with the subarachnoid space. The terminal cyst is lined by ependyma and dysplastic glia, is directly continuous with the dilated central canal of the cord, and probably represents a ballooned terminal ventricle. Patients with terminal myelocystocele have normal intellectual potential and are usually born without neurological deficit, so these defects must be identified and repaired early, before the onset or progression of lower extremity pareses.