Gliosarcoma with osseous tissue: an occasional metaplastic component.

Glioosarcomas represent a rare entity of intrinsic CNS neoplasms consisting of glial and sarcomatous elements; they account for 2 % of glioblastomas. There have been few reports of metaplastic osseous transformation in gliosarcomas. Here we report a rare case of gliosarcoma with metaplastic osteoid in a 57-year-old male patient. Magnetic resonance imaging revealed a large solid cystic heterogeneous mass lesion in the left temporal lobe with peri-tumoral oedema and areas of calcification. Histology revealed a grade IV tumour with neoplastic glial and mesenchymal components with myxoid change and areas of necrosis. The sarcomatous areas contained regions of benign osteoid formation. The histogenesis of the osseous element in gliosarcomas is not well understood, and could be a result of a metaplastic change or divergent differentiation from a common progenitor cell. The osseous tissue may be in the form of newly formed osteoid, benign bone tissue formation with lacunae and osteoblastic rimming, or unequivocally malignant tissue resembling an osteosarcoma.