Neurocristic cutaneous hamartoma: a distinctive dermal melanocytosis with an unknown malignant potential.

Neurocristic hamartomas (NCHs) result from aberrant development of the neuromesenchyme. In addition to a dermal melanocytic component, these tumors can contain neurosustentacular and fibrogenic components and can undergo malignant transformation. Although NCHs have many features in common with other dermal melanocytic neoplasms, including cellular blue nevi and some congenital nevi, they have distinctive clinical and histologic features. We present a case report of a 27-year-old white woman with an NCH of the scalp. The clinical, histologic, and immunohistochemical features are compared with those of other dermal melanocytic neoplasms. The NCH contained epithelioid pigmented melanocytes positive for S-100 and HMB45, within which there were well-circumscribed nodules of S-100+/Leu 7+/HMB45- cells surrounded by a capsule composed of spindle cells positive for epithelial membrane antigen. The stromal cells throughout the tumor were diffusely CD34 positive, and hair follicles were decreased and dystrophic within the tumor. NCHs represent neoplastic dysplasia that involves not only melanocytic cells but also neurosustentacular and fibrocytic effector cells. The histologic and immunohistochemical features, along with the decreased and dystrophic hair follicles, suggest that the abnormalities in the mesenchyme are significant and result from the contribution of neural crest cells to the cellular and matrix components of the mesenchyme.