Osteoid Osteoma

A frontal view of the right femur of a teenage boy demonstrates an ill-defined sclerotic area (arrows) in the proximal diaphysis with thickened cortex.

A coronal-reformatted CT image shows a well-defined lucency (arrow) within the central portion of sclerotic medulla. Within that lucency, a tiny calcific nidus is seen. Thickened cortex is also observed.

Facts: Osteoid Osteoma

• Self-limited benign osteogenic tumor consisting of a vascular mass (nidus) surrounded by reactive bone sclerosis
• Male predominance (male:female = 2:1). Teenagers and young adults (90% of cases between 5-30 years old)
• Characteristic pain referring to the nearest joint, worse at night. Pain is relieved by aspirin or NSAIDs
• Treatment options: surgical excision, CT-guided percutaneous resection or destruction of the nidus

Imaging Appearance

• Location: cortex, medulla or periosteum (anywhere but cortex most common)
• Long bones of lower extremity (esp femoral neck) most commonly affected. Almost never seen in flat bones and craniofacial bones
• Central lucent area (nidus) surrounded by sclerotic bone (nidus may be subtle and has variable degree of calcification)
• CT is helpful to identify the nidus (as in our case)
• MRI can be misleading because reactive bone marrow edema and soft tissue involvement may mimic malignancy

Our case: osteoid osteoma centered in the medullary cavity. The diagnosis was confirmed by CT (showing a lucent nidus with calcification) and clinical picture.

Reference:

Kadir S. Teaching Atlas of Interventional Radiology, 2005.

Vioria VJ, et al. Orthopaedic Pathology,