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,
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