CT scan evidence of dysthyroid optic neuropathy

Purpose: To determine the utility of CT imaging in identifying patients with dysthyroid optic neuropathy. Methods: Orbital CT scans of 12 randomly selected patients with dysthyroid optic neuropathy and 15 control subjects with Graves orbitopathy were retrospectively reviewed by two investigators blinded to the clinical data. The clinical diagnosis of optic neuropathy was made by one author before obtaining CT images and was based on clinical features. Results: Optic nerve crowding (P<0.001) and intracranial fat prolapse (P<0.05) were the imaging features independently related to optic neuropathy. A muscle index greater than 50% had excellent sensitivity (100%) but did not have high specificity (47%) for dysthyroid optic neuropathy. Superior ophthalmic vein dilation and proptosis did not show significant relations with optic neuropathy. Conclusions: This study suggests that patients with Graves orbitopathy who have severe optic nerve crowding, intracranial fat prolapse, and/or muscle index greater than 50% present on orbital CT scans are more likely to have coexisting optic neuropathy.