[Magnetic resonance imaging of sacral insufficiency fractures: characteristic features and differentiation from sacral metastasis].

Seven patients with sacral insufficiency fractures and seven patients with sacral metastasis were studied with MR imaging. The diagnoses were confirmed with other imaging modalities and clinical follow-up. The insufficiency fractures appeared as bands of abnormal signal: low signal intensity on T1-weighted images and slightly low to iso signal intensity on T2-weighted images. The lesions were delineated better on T1-weighted images than on T2-weighted images. The sacral alae were involved in all patients; five patients had bilateral lesions. The lesions that run across the sacral body were seen in three cases. Inclined coronal images were useful in demonstrating the pattern of distribution of the sacral insufficiency fractures. In three patients with follow-up MR studies, the lesions were markedly reduced or disappeared. The sacral metastatic tumors were of low signal in density on T1-weighted images and iso to high signal in density on T2-weighted images. The extent and distribution patterns of the lesions were various. It is possible to differentiate sacral insufficiency fractures from sacral metastases based on their distribution patterns on MRI. However, if the diagnosis is uncertain or if the symptoms persist or become worse, follow-up MR studies may be necessary.