Epiphyseal pseudotumor of the tibia:an uncommon presentation of osteoarthritis.

Epiphyseal pseudotumor secondary to osteoarthritis are rare in patients under 50 years. We report here the case of a 48-year-old woman who complained of pain in the medial side of the left knee for three years. X-rays of the left knee showed a large lytic lesion containing multiple septae, with sclerotic margins at the upper end of the tibia, associated with knee osteoarthritis. An epiphyseal tumor of the left tibia was suspected. CT scan of the left knee concluded in a giant subchondral cyst secondary to osteoarthritis. Subchondral cysts or geodes are a common finding in patients with knee osteoarthritis. Nevertheless, some unusual aspects of the lesions may lead to diagnosis difficulties.