Parosteal osteogenic sarcoma arising in cranial bones: clinical and radiologic features in eight patients.

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Parosteal osteogenic sarcoma is a distinct surface bone tumor with a better prognosis than conventional osteogenic sarcoma. We studied eight histologically proved cases of cranial parosteal osteogenic sarcoma. The tumors were identical in histologic appearance to parosteal osteosarcoma arising in long bones. Clinically, the tumor presented as a hard, painless, nodular scalp mass. The prevalence in women outnumbered that in men by 3:1, with most cases occurring between the second and third decades of life. Plain radiographs showed a rounded, sessile bone growth of variable size arising from the outer table of the skull. The tumor was heavily ossified centrally with variable margins and, at times, with radiating bony spicules at the periphery. No satellite bone nodules were noted in adjacent soft tissues. In three cases a fine radiolucent cleft was demonstrated between the tumor and the underlying outer table on the tangential radiographs or CT. After en bloc resection of the tumor, follow-ups for 20 years in one patient and 1 year in two patients showed no recurrence. Parosteal osteosarcoma of the skull is a rare low-grade tumor that usually arises from the outer table of the skull and has distinctive radiologic features that should distinguish it from other exophytic cranial bone neoplasms.