[Epiphyseal tibial osteoblastoma: report of a rare localization and review of the literature].

Osteoblastoma is an uncommon benign bone tumor diagnosed in about 1% of primary bone tumors. Predominantly observed in the axial skeleton, it can be observed in long bones (20%), generally in the diaphysis (80% of the long bone localizations). In typical cases, standard imaging is highly suggestive of the diagnosis. The typical image is a "lytic" zone surrounded by bony condensation, and a minimal osteosclerotic reaction peripherally, rarely invading the soft tissues. Diagnosis is confirmed at pathology: osteoblast-like cells disseminated in an abundant conjunctive background surrounded by immature richly vascularized bone. The tumor we report presented an unusual localization and an atypical aspect on the imaging studies. Located in the tibial epiphysis, this osteoblastoma invaded the soft tissues, as seen on the CT and MRI studies which visualized an encapsulated tumor with a calcified shell and a liquid-like tumefaction suggestive of a tumor arising from the synovial.