Eruptive vellus hair cysts: case report and review of the literature.

A 6-year-old Caucasian girl had dozens of asymptomatic, flesh-colored, 2- to 5-mm eruptive vellus hair cysts. These papules on the buttocks, thighs, and groin increased in number for three months. Histologic examination revealed poorly defined, keratin-filled cysts in the upper middermis, containing numerous transversely or obliquely cut portions of vellus hair. The histopathologic differential diagnosis with other epithelial cysts containing hair shafts is debated, and new clinical differential diagnoses are proposed. Review of the literature suggests that eruptive vellus hair cyst is not a rare disorder, but its frequency is probably underestimated due to paucity of symptoms. Nevertheless, the clinical relevance of some of the differential diagnoses should convince clinicians to obtain histologic confirmation.