Spectrum of nonterminal myelocystoceles

OBJECTIVE: To present the magnetic resonance imaging features, clinical findings, and possible embryologic bases for nonterminal myelocystoceles, a distinct subset of closed spinal dysraphisms. METHODS: We retrospectively analyzed imaging series and clinical records from five newborns and one older child with skin-covered soft tissue masses along the posterior midline spine. Spinal (6 patients) and brain (5 patients) magnetic resonance imaging was performed before surgical repair and compared with clinical findings, observations at surgery, and final lesion histology. RESULTS: The lesions affected the cervical (n = 3), thoracic (n = 2), and lumbar (n 1) regions. In each case, the dome of the mass was covered by thickened, dystrophic epithelium with no subcutaneous fat, whereas the base and lateral walls of the mass were covered by normal skin. All patients were neurologically intact at presentation. In three cases, a stalk emanated from the dorsal normal spinal cord, crossed a narrow posterior bony Spina bifida, and coursed through a posterior meningocele to attach to the inner aspect of its dome. The other three cases showed dissection of a hydromyelic cavity into the stalk, converting it into a second "cyst" within the meningocele. Concurrent anomalies included focal hydromyelia immediately cranial to the origin of the posterior stalk (n = 2), mild Chiari 11 malformation (n = 3), triventricular hydrocephalus from aqueductal stenosis (n = 1), filar lipoma (n = 1), and presumed neurenteric cyst (n = 1). At surgery, the sac was resected in all cases, but intradural exploration and untethering was performed in only three children. Embryologic considerations indicate that the spectrum of these lesions likely arises from partial limited closure of the neural tube, failed disjunction of the cutaneous ectoderm, and variable degrees of hydromyelia. CONCLUSION: The nonterminal myelocystocele is a distinct form of closed spinal dysraphism characterized by a skin-covered meningocele, which is either crossed by a fibroneurovascular stalk that extends from the dorsal aspect of the spinal cord to attach to the dome of the meningocele (abortive form, or myelocystocele manque) or contains a hydromyelic cavity that is continuous with the ependymal canal of the spinal cord (complete form).