MAGNETIC-RESONANCE-IMAGING IN OSTEOID OSTEOMA

The purpose of this study was to determine magnetic resonance imaging (MRI) features of osteoid osteomas and to evaluate the place of MRI in the diagnostic workup of suspected osteoid osteoma by comparing its diagnostic value with that of computed tomography (CT). Nine patients with radioclinical features highly suggestive of osteoid osteoma were investigated using bone scintigraphy, CT scan and MRI. MRI sequences were weighted for T1 (TR : 500 ms-TE : 34 ms), T2 (TR : 2000 ms-TE 50-100 ms) and T1 after intravenous injection of gadolinium-DTPA contrast material. The appearance of the nidus and surrounding area were analyzed, as well as the accompanying inflammatory reaction involving the bone marrow, soft tissues or synovium. All patients had surgical treatment. Clinical recovery was achieved in every case. Histological studies confirmed the diagnosis of osteoid osteoma in 7 patients. In two cases, histological confirmation was not obtained and the exact nature of the lesion therefore remained in doubt, although clinical and scintigraphic findings as well as the subsequent course were consistent with the diagnosis of osteoid osteoma. In 5 cases, MRI proved inferior to CT scan for detecting the nidus. MRI disclosed edema of the bone marrow not seen on CT scan sections in 5 cases, edema of the soft tissues in three cases, and synovitis with joint effusion in one patient with an epiphyseal osteoid osteoma. At present, MRI plays only an ancillary role in the diagnosis of osteoid osteoma, which rests on the concomitant use of bone scintigraphy and CT scan. However, MRI can provide additional evidence to support the diagnosis of clinically suspected osteoid osteoma when CT scan findings are not conclusive.