Histologic features of scalp melanocytic nevi.

Abstract

The scalp has been proposed as an anatomic site that harbors melanocytic nevi with distinctive histologic attributes, so-called "special-site" nevi, similar to nevi on the breast and genitalia. However, detailed studies are lacking. We sought to better delineate the features of scalp melanocytic nevi, particularly lesions that may qualify as special-site nevi. The histologic features of 365 total melanocytic nevi of the scalp were studied from 322 patients over a consecutive period of 18 months from July 2007 through January 2009. A total of 56 nevi with characteristic features were identified. The most common features were: (1) random melanocytes containing large nuclei (92.9%) and abundant pale cytoplasm with dusty melanin granules (96.4%); (2) large nests (76.8%) situated along the sides of rete and between rete ridges (85.7%); (3) nests of poorly cohesive melanocytes (82.1%); (4) overlap features with Clark nevi (75.0%); and (5) overlap features with superficial congenital nevi (50.0%). Pagetoid spread (14.3%), asymmetry (23.2%), and poor lateral demarcation (16.1%) were less common. These 56 lesions predominated in the first 2 decades of life and were not observed after age 35 years. Lack of long-term clinical follow-up of patients is a limitation; however, no recurrences or malignancies from these patients' scalps were submitted in the time period (≥ 3 years) since the initial biopsies. A special site scalp nevus is recognizable amongst scalp melanocytic nevi, and this lesion is more common in younger patients. Familiarization of its features should assist in the diagnosis and management of scalp melanocytic lesions.