MRI of extraocular orbital diseases

The author investigated the usefulness of MRI in the diagnosis of extraocular orbital diseases, and the diagnostic ability of MRI was compared with that of CT. The materials consisted of 38 cases of diseases in extraocular orbital region (all cases were examined with MRI and 34 of them were also examined with CT). MRI was performed with spin echo or STIR sequences using a 1.5 tesla superconductive unit (GE SIGNA). CT was performed using SOMATOM CR and DR-H. The study showed that MRI was equally or more useful than CT in detecting lesions as well as assessing the internal architecture and extension of the lesions. Differentiation between benign and malignant tumors by MRI is difficult from their signal intensity only and can be made from their extraorbital extension, just as by CT. In Graves' orbitopathy, T2-weighted images were more sensitive in reflecting its new or old pathological changes than CT. T1-weighted images enhanced with Gd-DTPA were useful in differentiating sphenoid wing meningiomas from other tumors, but not useful in assessing the degree of intraorbital extension. STIR sequences were particularly useful in the diagnosis of optic nerve atrophy and expectd to be applied to the lesions which were not detected or poorly demonstrated with CT and spin echo sequences. (author)