MRI in Graves orbitopathy: recognition of enlarged muscles and prediction of steroid response.

The purpose of this study is to compare MRI to CT in the recognition of Graves orbitopathy and to compare MRI to clinical examination in the prediction of steroid response. Sixteen patients with dysthyroid orbitopathy (21 orbits) were examined by CT and MRI; muscle enlargement was measured by ultrasonography. Sensitivity in recognizing enlarged muscles was 85.4% for CT and 61.2% for MRI; CT recognized all affected orbits but 1, while MRI failed in 4 cases. Clinical inflammatory signs (p = 0.17) were more reliable predictors of steroid response than muscular T2 hyperintensity on MRI (p = 0.64). In a patient where histological examination documented edematous changes, MRI failed to reveal edema. MRI adds no morphologic information to CT; moreover, T2 intensity is less specific than clinical examination in documenting active disease and forecasting therapeutic outcome.