Osteoid Osteoma

Findings: There is a cortically based lytic lesion with surrounding sclerosis and cortical new bone formation.

Discussion: Osteoid osteomas are lesions with less than 2cm nidus of osteoid/woven bone in vascular tissue. 75% of osteoid osteomas are cortically based, 25% are cancellous based. They usually occur in the meta/diaphyses of long bones, typically the femur and tibia.

The differential diagnosis includes:
- Brodies Abscess
- enostosis (bone island)
- osteoblastoma (>2.5 cm)
- osteoma (cold on bone scan)
- stress fracture (linear lucency)

Source: http://www.statdx.com