A 54-year-old female was referred to our institution with a 1-week history of headaches. Her past medical history was unremarkable. Magnetic resonance imaging (MRI) revealed a large, partially necrotic and calcified tumor in the parenchyma of the left frontal lobe with marked surrounding edema and mass effect on midline structures, but without any dural attachment. The tumor appeared hypointense on non-contrast T1-weighted images (Fig. 1a) and iso-to hyperintense on T2-weighted images (Fig. 1b). The enhancement of the tumor was irregular and most prominent at its periphery (Fig. 1c–e). The preoperative clinical diagnosis was meningioma or calcified glial tumor. She underwent incomplete resection of the tumor and histopathologic examination revealed a malignant mesenchymal neoplasm displaying a poorly differentiated spindle cells with interspersed eosinophilic osteoid production, calcification intimately associated with the malignant cells, and localized new bone formation (Fig. 1f). Immunohistochemistry was negative for epithelial membrane antigen (EMA), glial fibrillary acidic protein (GFAP), CD34, desmin and neurone specific enolase (NSE) but positive for vimentin (Fig. 1g), P53 (Fig. 1h), osteopontin (Fig. 1i) and osteonectin (Fig. 1j). Antisera against the proliferation marker Ki-67 revealed very variable immunoreactions (80%). Given the microscopic appearance a histopathologic diagnosis of primary intracerebral osteosarcoma was made.
Extraskeletal osteosarcoma is rare and is defined as a malignant mesenchymal neoplasm that produces osteoid as well as bone or chondroid material and is located in the soft tissue without any bony attachment (Chung and Enzinger 1987). Primary intracranial osteosarcoma most often represent intracranial invasion from a tumor arising from the skull (Salvati et al. 1993), and meningeal osteosarcomas which arise from the mesenchymal components of the meninges are also reported (Dagcinar et al. 2008). However, primary intracerebral osteosarcoma is rare with very few reported cases in literature.