Osteoma of the mastoid.

We present herein a rare case of osteoma mixtum of the mastoid. The main features of the osteoma were demonstrated clearly by preoperative tangential X-ray projection. Histological studies revealed the osteoma to be composed of multiple small foci of ossification on the outer layer with a large single inner mass. Subsequent examinations revealed that the osteoma had arisen from the parietosquamosal suture.