Hair Follicle Nevus

Abstract

Congenital nonmelanocytic nevi include epidermal nevi, connective tissue nevi, sebaceous nevi, hair follicle nevi, and proliferations of other dermal and subcutaneous structures including smooth muscle and adipose tissue. Such lesions often involve the skin of the head and neck region and are sometimes associated with syndromes of genodermatosis. Tumors with follicular differentiation include a large variety of lesions that recapitulate various structures of the hair follicle. Numerous classifications of hair follicle tumors are proposed by experts in the field with limited consensus. Hair follicle nevus, or congenital vellus hamartoma, is an extremely rare lesion of the hair follicle with only scattered case reports in the English literature. The lesion most commonly presents at birth as a small papule on the head and neck area and represents a follicular hamartoma with a high degree of differentiation toward the hair follicle. We report another case of 2 hair follicle nevi occurring in the same adult patient. Immunohistochemical profiling of hair follicle tumors, though most useful in differentiating basal cell carcinoma from trichoepithelioma, is also helpful in characterizing the morphology and thus classification of benign follicular neoplasms such as follicular hamartomas and hair germ tumors. As the immunohistochemical features of hair follicle nevus have not yet been evaluated, we additionally report the staining characteristic of this entity using CD34, bcl-2, and CD10 immunohistochemical stains.