Quantitative CT of the orbit in Graves' disease.

In order to determine the value of quantitative CT of the orbit in patients with Graves' disease, we clinically examined 174 orbits of 87 patients with Graves' disease and evaluated them by CT in respect to the density and size of the extraocular muscles, the globe position and the width of the optic nerve-sheath complex. We also determined the normal ranges for density of extraocular muscles in 200 normal orbits of 100 patients for comparison. Normal ranges for the density of extraocular muscles were (mean +/- 2 SD) medial rectus, 28-63 HU; lateral rectus, 24-78 HU; inferior rectus, 20-64 HU; superior muscle group, 28-62 HU. 51 of 77 (66%) patients with Graves' disease had extraocular muscle density changes. Some extraocular muscles showed fatty infiltration on CT. 50 of 87 (57%) patients had at least one enlarged extraocular muscle, 47 (54%) patients had exophthalmos and 59 (68%) patients had either exophthalmos and/or extraocular muscle enlargement. A diagnosis of Graves' ophthalmopathy was made in 69 of 87 (79%) patients using CT and in 50 (57%) patients by clinical examination. We conclude that quantitative CT imaging of the orbit with evaluation of the size and density values of extraocular muscles and the globe position may be very helpful in detecting ophthalmopathy in patients with Graves' disease.