Abstract
We report a rare case of malignant hemangiopericytoma (MHP) arising from the ulna of an eight year-old boy. X-ray findings revealed expansive lytic lesions with bubble appearance in the distal metaphysis of the right ulna. Computed tomography showed no cortical destruction. By magnetic resonance imaging, the lesion was highly enhanced with gadolinium. Histologically, the oval tumor cells tended to cluster around numerous capillaries. Reticulin stain revealed that proliferating neoplastic cell were hemangiopericytes. Vimentin and HLA-DR were positive, while SMA, myoglobin, desmin, EMA, cytokeratin and S-100 were negative. Ultrastructure of MHP revealed pinocytotic vesicles and distinct basal laminae. After preoperative chemotherapy, the tumor was removed en-bloc, and one forearm bone was adopted for the reconstruction MHP of bone is reported to be only 0.1% of all malignant primary bone tumors. Also, the presented case was the youngest and the only ulna case ever reported.