Two cases of atypical membranous aplasia cutis with hair collar sign: one with dermal melanocytosis, and the other with naevus flammeus.

Summary We report two atypical cases of membranous aplasia cutis surrounded by a rim of hairs, one case associated with dense dermal melanocytosis and the other with naevus flammeus, with characteristic clinical features. A rim of hypertrichosis, ‘hair collar’ sign, is proposed to have a close association with neuroectodermal defects. A failure of the normal closure of the cranial neural tube might have affected foetal skin development, including melanoblast migration and capillary network formation. The changes in the present cases, as well as the hair collar sign may suggest a complex hamartomatous nature of membranous aplasia cutis.