Brodie's Abscess Following Radiofrequency Ablation of an Atypical Osteoid Osteoma

A 15 years old boy presented with an atypical osteoid osteoma (OO) in distal femur. He underwent radiofrequency ablation (RFA) elsewhere. He presented to our centre a year later with persisting pain. MR scan showed incomplete ablation of the nidus as there was only a single pass of the RF probe for a 14 mm long linear lesion. We also found penumbra sign and wall enhancement on contrast MRI suggestive of a Brodie's abscess (BA). Under CT guidance the OO was drilled and BA was saucerised. Following this he was treated with culture sensitive antibiotics and his symptoms resolved. BA and OO are common differential diagnoses. RFA of OO leading to BA has not been reported in literature. Atypical linear OO requires multiple probe placements to ablate the long nidus. Diligent care should be taken to avoid intraoperative contamination in CT room which could lead to infection.