Thyroid associated orbitopathy
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CT of the orbits demonstrates marked fusiform thickening of the inferior rectus, medial rectus and superior rectus muscles bilaterally. The result is proptosis.
CT is the most commonly used modality due to its widespread availability and rapid image acquisition. Contrast, although ideal, is not necessary as the natural contrast between orbital fat and muscle allows for adequate delineation of the orbital content, as it is possible to check on this case.
The order of extraocular muscle involvement can be remembered by the mnemonic I'M SLOW, and bilateral (76-90%) and symmetric (70%) involvement is typical. The tendon is typically spared (although it can be involved in acute cases) with the swelling largely confined to the muscle belly.