Primary extraskeletal osteosarcoma in the pineal region. Case report.

Primary extraskeletal osteosarcoma occurring in the brain parenchyma is distinctly uncommon, with only five cases having been reported. The authors describe the case of a 45-year-old man who presented with progressive headache and diplopia. Computerized tomography scanning and magnetic resonance imaging results revealed a pineal region tumor with obstructive hydrocephalus. The patient underwent partial resection of the tumor. The histological examination showed large pleomorphic tumor cells embedded in osteoid matrix. Immunohistochemical analysis was negative for various antibodies and thus excluded a glial, germ cell, epithelial, and lymphoid tumor origin. Only vimentin showed strong positivity in most of the tumor cells. Ultrastructurally, the tumor cells were rich in dilated rough endoplasmic reticula. Clear zones between tumor cells and osteoid matrix were observed. The osteoid matrix was made up of small collagen fibrils and hydroxyapatite deposits. The tumor was not attached to the bone structure of the skull. These findings are consistent with the features of extraskeletal osteosarcoma. Data from complete medical and radiological studies excluded a metastatic origin for this tumor. Partial resection and postoperative radiotherapy had provided tumor control at 11 months after the onset of symptoms. This is the first reported case of a primary extraskeletal osteosarcoma occurring in the pineal region.