RESUMO
INTRODUCTION: Osteosarcoma is a malignant mesenchymal tumor including cells that present an osteoblastic differentiation. On the skull, it has often extra-axial development associated with bone reaction. We report an atypical and rare case of intracranial or cerebral osteosarcoma underline the radiological and pathological diagnostic difficulties. CASE REPORT: Our case concerns a primary osteosarcoma without bone involvement in a 10-year old boy who was admitted for intracranial hypertension with progressive worsening and brachial monoparesis. Subtotal resection was performed but the postoperative course was not favorable. The child died five months after the initial surgery. Its radiological aspect prompted us evoke several diagnoses including glioma or meningioma. On the histological level, osteosarcoma, especially with poorly differentiated cells, can be deceiving with other processes, including a gliosarcoma that was revealed by simple microscopic reading before being confirmed by an immunohistochemical study. CONCLUSION: In the absence of any bone reaction or known extra-cranial location, it can be difficult to suggest the diagnosis of osteosarcoma based on imagery alone. Immunohistochemistry is essential for an accurate diagnosis.