ENLARGEMENT OF THE TENSOR INTERMUSCULARIS MUSCLE IN GRAVES OPHTHALMOPATHY - A COMPUTED TOMOGRAPHIC AND MAGNETIC-RESONANCE-IMAGING STUDY

Objective: To determine whether the tenser intermuscularis muscle (TIM), which consists of muscle fibers in the superolateral intermuscular orbital septum, is involved in Graves' ophthalmopathy (GO). Design: The computed tomographic (n=24) and magnetic resonance imaging (n=10) appearances of the TIM were retrospectively examined in 34 patients with known GO. The severity of GO was assessed by applying a scoring system from 0 to 3 (ie, normal [0], mild [1], moderate [2], and severe [3]) to each of the rectus muscles and superior oblique muscle. The severity of exophthalmos, enlargement of the superior ophthalmic vein, and displacement of the lacrimal gland were also recorded. Results: The TIM appeared as thickening of the septum immediately behind the globe, and it was best seen on coronal. magnetic resonance images. There was enlargement of the TIM in 19 of the 34 patients, and it was bilateral in 17. Enlargement was present only in patients with moderate or severe involvement of other muscles (muscle index, >7/15), and it was significantly correlated with the muscle index (P<.05), exophthalmos (P<.05), enlargement of the superior ophthalmic vein (P<.005), and anterior displacement of the lacrimal gland (P<.01). Severe enlargement of the TIM was seen in only five of the 34 patients, and it showed a close correlation with the muscle index (P<.005), exophthalmos (P<.001), enlargement of the superior ophthalmic vein (P<.001), and anterior displacement of the lacrimal gland (P<.001). Conclusions: Enlargement of the TIM in GO can be identified on computed tomographic and magnetic resonance imaging scans. It is invariably associated with moderate or severe involvement of other extraocular muscles, and it correlates closely with other well-recognized imaging features of severe GO.