Osteoid osteoma is a benign skeletal neoplasm composed of osteoid and woven bone.

Its incidence is app. 11% of all bone tumours.

Age: 10-25 years.

2:1 male predominance.

50% of cases occur in the femur and tibia with predilection for upper end of femur particularly the neck and trochanters. App. 10% of cases occurs in the spine, most of these affecting the neural arch.

Clinically it presents as severe pain, worse at night, which is dramatically alleviated by the use of aspirin.

Pathologic feature of the tumour is a nidus that is usually 1 cm or less in diameter. Most common location within the bone is in the cortex, with intramedullary and subperiosteal lesions also occurring.

The characteristic appearance of a cortical lesion is as a radiolucent nidus surrounded by florid perifocal reactive sclerosis. The site of the tumor determines the degree of bone sclerosis. In medullary tumors, sclerosis is minimal or absent. Cortical and subperiosteal tumors provoke considerable sclerosis. Long-standing tumors demonstrate more sclerosis. Children also mount more of a sclerotic response than do adults. 60% of spinal lesions occur in the lumbar spine, usually creating an ivory pedicle or neural arch.  CT is the ultimate diagnostic tool for the precise localization of the nidus. Intra-articular lesions cause synovial thickening or inflammation and joint effusion, which may be readily apparent on MRI.   Radionuclide bone scanning of uptake of technetium-99m phosphonates shows intense activity at the site of the tumor.

Several techniques are available for ablation of osteoid osteoma. The tumour can be percutaneously ablated by using radiofrequency (RF), ethanol, laser, or thermo coagulation therapy under CT guidance.