Osteoid Osteoma of Calcaneum

Osteoid osteoma is a benign osteoblastic tumor of the bone which is composed of osteoid and atypical bone which was first described by Jaffe in 1935. It usually occurs in males (2:1) in 10-20 yr of age group. Typical clinical features are pain worsening at night which relieves on ingestion of analgesics. It is commonly seen in the long bones, proximal femur and diaphysis of tibia. 10% occur in bones of foot, 2-3 % in calcaneum. Radiologically, it is characterized by nidus which is composed of osteoid and osseous tissue within highly vascularised connective tissue matrix. It is mostly less than 10mm in diameter. CT and X-ray show intracortical nidus which is sometimes surrounded by medullary sclerosis. MR shows hypointense sclerosis with central nidus which appears iso to hypointense on T1 WI and iso to hyperintense on T2WI with surrounding marrow edema. Double lesion sign is seen on radionuclide scan. Treatment includes surgical excision of nidus and surrounding sclerotic bone OR CT guided radiofrequency ablation of the nidus.