Omphalokeratolith.

A 69-year-old woman presented with a firm, black umbilical mass of unknown duration. It was easily removed with a warmed otic glycerin preparation. Histologic examination showed that it contained laminated keratin, amorphous material resembling sebum, numerous terminal hairs, and scattered collections of bacteria. Moderate amounts of argentaffin staining material were detected throughout the specimen, and the black color of the lesion was probably due to melanin and oxidized lipids, much like an open comedone. The mass is appropriately called an omphalokeratolith.