Recognition and differential diagnosis of enlarged extraocular muscles in computed tomography.

We found enlargement of the extraocular muscles in 70 patients out of 603 orbit studies, of whom 310 had exophthalmos. The majority (46 of 70) had the eye signs of Graves' disease. Arteriovenous malformations and carotid cavernous fistulas can cause enlargement of the extraocular muscles by a diffuse increase in orbital venous pressure, Acute orbital myositis can be distinguished from other forms of pseudotumor by the presence of a single enlarge extraocular muscle with associated inflammatory findings which responds to corticosteroid therapy. Neoplasms may invade extraocular muscles or compress their venous drainage causing secondary muscle enlargement. In all these patients the presence of a mass was correctly identified. The ability of the computed tomography scanner to recognize abnormalities of the extraocular muscles represents a significant advance in classification and diagnosis of the causes of exophthalmos.