Osteoid osteoma is a small, benign but painful lesion with specific clinical and imaging characteristics. Computed tomography is the imaging modality of choice for visualization of the nidus and for treatment planning. Complete surgical excision of the nidus is curative, providing symptomatic relief, and is the traditionally preferred treatment. However, surgery has disadvantages, including the difficulty of locating the lesion intraoperatively, the need for prolonged hospitalization, and the possibility of postoperative complications ranging from an unsatisfactory cosmetic result to a fracture. Percutaneous radiofrequency (RF) ablation, which involves the use of thermal coagulation to induce necrosis in the lesion, is a minimally invasive alternative to surgical treatment of osteoid osteoma. With reported success rates approaching 90%, RF ablation should be considered among the primary options available for treating this condition.
Figure 1. Unenhanced axial CT image shows a welldefi ned complex cystic mass within the left upper quadrant. The mass contains multiple smaller, peripheral, thin-walled cysts with variable but predominantly low attenuation within a fl uid matrix (*). History A 44-year-old woman with no signifi cant medical history presented with urinary urgency and left fl ank pain. The patient was originally from Armenia and had been living in the United States for the past 20 years. At physical examination, the patient was afebrile, and there was palpable fullness in the left upper quadrant of the abdomen and left fl ank with no tenderness. Initial laboratory test results were normal except for an elevated white blood cell count of 14 (normal range, 4-11) and microscopic hematuria. Unenhanced computed tomography (CT), which was performed for evaluation of urinary tract calculus disease, resulted in the incidental discovery of a large, multiloculated, cystic left renal mass. The patient underwent subsequent multimodality evaluation.
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