Neuroectodermal neoplasms arising in congenital nevi.

Congenital giant nevi of neuroectodermal origin are composed predominantly of melanocytes and occasional neural elements. Neoplasms arising in such nevi may be morphologically heterogeneous with variable clinical behavior. We report the case of a female infant born with multiple pigmented nevi, including a giant hairy nevus of bathing trunk distribution in which arose a large pedunculated mass involving the sacral region, buttocks, perineum, and left thigh. Within this neoplasm, mixtures of neural crest-derived tissues having both melanocytic (nevus) cell and neural supportive (neuroid of Schwannian) cell differentiation were identified. The neural differentiation, which was seen in the dermis and subcutaneous tissue, had a neurofibromatous appearance and demonstrated multiple pseudomeissnerian corpuscles. In addition, at 16 months of age the child developed a malignant melanoma in the flank region of this congenital giant nevus. The morphologic pluripotentiality of the primitive neural crest derivatives in congenital nevi has only recently been elucidated. These lesions should be regarded as neuroectodermal neoplasms and subclassified according to their differentiating histologic characteristics because prognosis and management are influenced by morphologic determinants.