Retained Medullary Cord of Skin-uncovered Saccular Type Requiring Differentiation from Myelomeningocele

Retained medullary cord is a form of closed spinal dysraphism proposed by Pang et al. It is thought to result from the failed regression of the medullary cord, giving rise to a non-functional cord-like structure. This cord-like structure is continuous with the functional cord and tethers it, thereby causing symptoms. We previously reported five patients with saccular retained medullary cord, in whom a cystically dilated dural cul-de-sac protruded outside the spinal canal. This protrusion occurred through sacral spina bifida at or below approximately the S2-3 level, where the dural cul-de-sac is located, and through the sacral hiatus, forming a sacral subcutaneous meningocele sac. In these cases, the retained medullary cord terminated at the apex of the sac. We report a patient in whom the lower half of the sac lacked skin coverage and contained a neural placode-like structure, necessitating differentiation from an open myelomeningocele. The infant had no neurological deficits. Surgery was performed on the second day after birth. A non-functional cord-like structure was resected at the cranial end of the surgical field, excised en bloc with the skin lesion, and cord untethering was performed. Histopathological examination revealed glial fibrillary acidic protein-immunopositive neuroglial tissue containing an ependymal lined central canal-like structure. The retained medullary cord tissue was directly exposed at the site where the skin was missing. Patients previously diagnosed with terminal apical myelomeningocele based solely on neuroradiological findings are likely to have saccular retained medullary cord. In such cases, prophylactic cord untethering is an important surgical consideration in addition to sac repair.