A small (< 2 cm) lucent nidus, often with central mineralisation, surrounded by dense reactive sclerosis — CT with thin sections finds the nidus that the sclerosis hides, and guides ablation.
Orient first
- Night pain relieved by NSAIDs in an adolescent or young adult.
- Cortical in long bones (femur, tibia), posterior elements in the spine (painful scoliosis).
- Intra-articular lesions cause synovitis and little sclerosis.
Acquire the study
- Radiograph first; thin-section CT (≤ 1 mm) with multiplanar reformats to find and localise the nidus; CT-guided radiofrequency ablation.
The manoeuvre
- Thin axial slices in bone window through the sclerosis: round nidus under 2 cm, measure in mm.
- Central mineralisation within the nidus; vascular groove sign.
- Location: cortical, medullary, subperiosteal, intra-articular — for the ablation route.
- Distance to nerves and skin for ablation planning.
What confirms it
- A nidus under 2 cm with surrounding sclerosis on CT in a patient with typical pain.
What licenses you to exclude it
- Thin-section CT through the painful site without a nidus makes osteoid osteoma unlikely.
The classic misread
- Calling it a stress fracture — a fracture line is linear, a nidus is round.
- Missing an intra-articular nidus with little sclerosis.