Parosteal osteogenic sarcoma of the mastoid bone.

Parosteal osteogenic sarcoma (POS) is an uncommon surface bone tumor, most often arising from the metaphyseal end of long bones. Involvement of the cranial bones is rare, with only 1 case of mastoid bone POS previously reported in the literature. Two patients with POS of the mastoid are presented, 1 followed up for 25 years after surgical treatment. The presenting signs and symptoms, as well as distinctive radiographic findings, are discussed. Histologic features are also described. Typically, cranial POS appears as a sessile, densely ossified surface growth with radiating bone spicules that blend with surrounding soft tissue. Treatment is en bloc resection, which is curative in most cases.