Plaque-like osteoma cutis with transepidermal elimination.

Osteoma cutis is a rare lesion that consists of the presence of bone tissue within the dermis and/or hypodermis. It may be classified as primary osteoma cutis, when bone tissue develops in the skin without any pre-existing lesion and secondary osteoma cutis, which is more frequent and occurs when osseous tissue develops on a pre-existing lesion. We present a case of primary plaque-like osteoma cutis involving the scalp, left forehead and left cheek, which appeared in an adult male. Histopathological study showed several islands of mature osseous tissue involving the full thickness of the dermis. In some areas, there was also transepidermal elimination of bone spicules. We review the literature about previously reported similar cases.