Periosteal osteoblastoma: A case report and a review of the literature

Osteoblastomas located on the surface of cortical bone, so-called periostea l (juxtacortical) osteoblastomas, are extremely rare. A 24-year-old man com plained of pain and swelling in the left knee. The clinical and radiologica l investigation showed a tumor located in the posterior portion of the dist al shaft of the femur. The radiological differential diagnosis included par osteal osteosarcoma, periosteal chondroma and periostitis ossificans. A fro zen section was obtained and histology revealed an osteoblastoma with large epithelioid-appearing osteoblasts consistent with an aggressive osteoblast oma. An en bloc resection of the tumor was performed and the definitive his tology of the whole specimen revealed a typical osteoblastoma. The authors draw attention to the fact that periosteal osteoblastoma is a rare tumor th at could be mistaken clinically and histologically for other and more commo n tumors at this location.