Atypical Presentation of an Osteoid Osteoma With a Multicentric Nidus.

An osteoid osteoma is typically a benign bone tumor affecting young adult males, often presenting with nocturnal pain alleviated by nonsteroidal anti-inflammatory medications (NSAIDS). It usually manifests as a solitary nidus with surrounding sclerosis. An osteoid osteoma with a multicentric nidus, characterized by multiple nidi, is a rare variant. A 12-year-old girl presented with a one-year history of worsening, nighttime pain in her upper left leg. Plain radiographs revealed two lytic lesions with sclerosis. A computed tomography (CT) scan confirmed two well-defined sclerotic lesions with central lytic lesions. Magnetic resonance imaging (MRI) demonstrated two hypointense lesions with peripheral hyperintensity on short tau inversion recovery (STIR) sequences, suggestive of osteoid osteoma with a multicentric nidus. Differential diagnoses included osteomyelitis with Brodie's abscess, osteoblastoma, chondroblastoma, and malignant lesions. Due to the atypical presentation and lack of experience with radiofrequency ablation (RFA) for multicentric cases, surgical excision was performed. Histopathology confirmed osteoid osteoma. After rehabilitation, the patient was asymptomatic at six months with no recurrence on radiographs. This case highlights the unusual presentation of osteoid osteoma with a multicentric nidus in a young female. Radiological workup with plain films, CT, and MRI was crucial for diagnosis. While RFA is gaining popularity, surgical excision remains a valid option, especially for atypical cases.