Extraocular Muscle Size Comparison Using Standardized A-scan Echography and Computerized Tomography Scan Measurements

Abstract

In many clinical situations, the standard for evaluating extraocular muscle (EOM) size, particularly in thyroid ophthalmopathy, has been use of the computerized tomography (CT) scanner. The impression is generally reported as “enlarged or normal EOMs.” If the report of “normal EOM” on CT scan weighs heavily against the diagnosis of thyroid eye disease, how does this qualitative assessment compare with the diagnostic modality of ultrasound? The technique of standardized A-scan measurement of extraocular muscles has been extremely accurate. In this paper, standardized A-scan measurements and CT scan estimates of EOMs are compared in a series of ten patients with a clinical diagnosis of Graves' disease. Three of ten patients displayed enlarged EOMs by CT interpretations; seven of ten patients were categorized as consistent with Graves' disease by correlation with current ultrasonographic criteria for muscle enlargement, asymmetry, and high irregularity of tissue reflectivity.