A 16-year-old boy has a 6-week history of dull aching pain in the distal femur, worse at night and relieved by aspirin. X-ray shows a small, well-demarcated radiolucent nidus (less than 1 cm) surrounded by dense reactive sclerosis in the cortex. What is the most likely diagnosis?

• A Osteoblastoma
• B Brodie's abscess
• C Ewing's sarcoma
• D Osteoid osteoma ✓

Explanation

Osteoid osteoma is a benign osteoblastic lesion characterised by a central nidus less than 1.5 cm surrounded by dense reactive bone. The hallmark is night pain dramatically relieved by NSAIDs (prostaglandin-mediated). It most commonly affects the cortex of the femoral and tibial shaft in adolescents and young adults. Osteoblastoma has a nidus greater than 2 cm and does not show the same NSAID response.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.