OSTEOID OSTEOMA - MR-IMAGING VERSUS CT

PURPOSE: To compare the performance of computed tomography (CT) and ma gnetic resonance (MR) imaging in diagnosis of osteoid osteoma. MATERIA LS AND METHODS: Nineteen patients with histologically proved osteoid o steoma underwent CT and MR imaging before excision of the lesion. CT a nd MR images were compared regarding lesion conspicuity and detection of marrow, soft-tissue, and/or synovial changes adjacent to the primar y lesion. RESULTS: CT was more accurate than MR imaging in detection o f the osteoid osteoma nidus in 63% of cases. MR imaging was better tha n CT in showing intramedullary and soft-tissue changes in all cases. T his may produce a misleading aggressive appearance on MR images. There was a statistically significant correlation between presence or absen ce of marrow or soft-tissue changes and treatment with antiinflammator y medications (P < .05). CONCLUSION: CT remains the best imaging modal ity for diagnosis of osteoid osteoma. MR images should not be interpre ted without reference to plain radiographs and CT scans if serious err ors in diagnosis are to be avoided.