Periosteal osteoblastoma of the distal femur.

Periosteal osteoblastoma is a rare benign osteoblastic bone tumour located on the cortical bone. We report a case of periosteal osteoblastoma located at the distal femur in a 31-year-old man. Clinical, radiological and histopathologic findings are described and differential diagnosis is discussed. Despite its rarity, periosteal osteoblastoma should be considered as a possible diagnosis together with periostitis ossificans, periosteal chondroma, periosteal osteosarcoma and parosteal osteosarcoma when confronted with a superficial bone lesion.