Pigmented follicular cyst.

This report describes the clinical and histopathologic characteristics of a pigmented follicular cyst. Clinically, it was a blue intracutaneous nodule that simulated a blue nevus. Nevertheless, the histopathologic examination showed in the mid dermis an epithelial cyst whose wall comprised a layer of stratified squamous epithelium with infundibular keratinization and whose lumen contained laminated keratin and many pigmented terminal hair shafts. The differential diagnosis with other epithelial cysts containing hair shafts in their cavities, mainly the eryptive vellus hair cyst, is discussed.