Unusual sacrococcygeal embryologic malformations with cutaneous manifestations.

Two unusual sacrococcygeal neuroepithelial heterotopias manifested as masses associated with cutaneous signs. In a 13-month-old infant, a cystic coccygeal medullary vestige was associated with a midline epidermal nevus. In another patient, a lipomeningocele with neuroepithelial heterotopia manifested as a skin tag and mass in the right buttock. In both cases, the malformations probably resulted from abnormal canalization and retrograde differentiation of the distal neural tube. Cystic coccygeal medullary vestige results from dilation of a persistent ependymal cyst present commonly in neonates at the distal part of the coccyx. The lipomeningocele appears to have arisen from an aberrantly formed ependymal canal. The embryologic events that gave rise to the lesions, the differential diagnosis of postrectal masses, and the common association of midline lesions of skin and soft tissue with neural defects are stressed.