A 15-year-old boy has a 3 cm painful swelling of the proximal tibia with night pain relieved by aspirin. X-ray shows a small radiolucent nidus (<2 cm) surrounded by dense reactive sclerosis. The diagnosis is:

• A Osteosarcoma
• B Osteoblastoma
• C Bone island (enostosis)
• D Osteoid osteoma ✓

Explanation

Osteoid osteoma is characterised by a central nidus (<2 cm, containing woven bone and fibrovascular tissue) producing prostaglandin E2, which causes intense night pain dramatically relieved by NSAIDs (aspirin). The surrounding reactive sclerosis is secondary to the nidus. Osteoblastoma is histologically identical but the nidus is >2 cm and is not reliably NSAID-responsive. Treatment: CT-guided radiofrequency ablation of the nidus is now the gold-standard minimally invasive treatment. Open surgical excision is reserved when RFA is not feasible.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.