Computed tomography of the normal thymus.

Abstract

Recognition of variations in size, shape and density of the normal thymus on computed tomographic (CT) scans is of paramount importance, lest it be misinterpreted as an abnormal mediastinal mass. Studying patients subsequently proved free of active chest disease, 154 CT scans of the mediastinum, performed on a 4th-generation scanner, were analyzed to determine the incidence of visualization and appearance of the normal thymus. The thymus was seen in 100% of patients under age 30 yr, 73% of patients between 30-49 yr and in 17% of patients over 49 yr of age. The thickness of the thymus showed a definite decrease in size with increasing age; although the width showed a similar general tendency, a wide variation was noted within each age group. In younger patients, the density of the thymus was similar to that of muscle; the attenuation values progressively decreased in older patients, finally approaching that of fat.