A 23-year-old female player presented with a six-month history of posterior thigh pain. While she related the onset of pain to playing football, she did not give a clear history of trauma. The pain reliably woke her from sleep (at about 4am) each night and was almost completely eliminated when she took oral ibuprofen before bed. A hanging leg test (fulcrum test) reproduced her thigh pain.
A lateral x-ray shows smooth cortical thickening of posterior femur. There is no aggressive periosteal reaction, evidence of fracture or soft tissue abnormality. On MRI there is a fusiform thickening of the posterior femoral cortex with a small intracortical focus of T2 hyperintensity. There was enhancement of the intracortical area after contrast. Subsequent CT imaging further demonstrates the cortical thickening and demonstrates an ovoid-shaped, lucent ‘nidus’. Appearances are most consistent with an osteoid osteoma.
This young woman was diagnosed with an osteoid osteoma based on her history and radiology findings. She has been referred for radiofrequency ablation of the lesion. This procedure is less invasive than surgical resection and is successful in up to 96% of cases.
Osteoid osteomas are a relatively common benign bone tumour. They are most frequently found in long bones, such as the femur and tibia, but can occur at any site. They generally present in younger patients (being most common before the third decade) and are approximately three times more common in males. The most common presenting symptom is pain. This is classically worse at night and is improved with oral NSAID.
Cortical thickening surrounding a small central core of lower density (the nidus) are the classical radiological finding. X-rays may be normal; however, the cortical thickening is generally well visualised with this imaging modality. The central ‘nidus’ is sometimes visible on x-rays as a well-circumscribed lucent region, occasionally with a central sclerotic dot. CT imaging is generally considered to be the imaging modality of choice. The nidus is generally best appreciated on this imaging modality appearing as a focally lucent area within surrounding sclerotic reactive bone. A biopsy may also be needed to confirm the diagnosis in some cases.
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