Graves ophthalmopathy: Intracranial fat prolapse on CT images as an indicator of optic nerve compression

PURPOSE: To determine the usefulness of a number of imaging features in the differentiation of patients with Graves ophthalmopathy who had optic neuropathy from those who did not. Intracranial herniation of orbital fat through the superior ophthalmic fissure and its clinical importance was also assessed. MATERIALS AND METHODS: The computed tomographic (CT) appearance of the orbital apex was examined in 50 patients without and in 50 patients with Graves ophthalmopathy. The clinical diagnosis of optic neuropathy was made by an ophthalmologist who was unaware of the imaging appearances and was based on clinical features and abnormalities of visual evoked potentials or changes at automated perimetry. RESULTS: Intracranial fat prolapse (P < .001) and optic nerve crowding (P < .05) were the only imaging features that were independently related to optic neuropathy. The presence of intracranial fat prolapse or optic nerve crowding on CT scans helped identify 16 of 17 patients with optic neuropathy. Sensitivity was 94%, specificity was 91%, positive predictive value was 69%, and negative predictive value was 98%. CONCLUSION: Intracranial fat prolapse correlates closely to the presence of optic neuropathy in Graves ophthalmopathy. This sign, in combination with optic nerve crowding, demonstrates a closer correlation to optic neuropathy than previously described imaging features.