Thymus in the superior mediastinum simulating adenopathy: appearance on CT

A soft-tissue nodule was identified in the mediastinum superior to the left brachiocephalic vein in six patients undergoing computed tomography (CT) of the chest. In one case, biopsy of the mass showed that it was thymic tissue. In the remaining cases, the nodule was identified as thymus on the basis of the CT findings. The findings include equal density of the superior mediastinal nodule and the thymic lobes anterior to the ascending aorta, no displacement or narrowing of adjacent arteries, absence of a fat plane between the nodule and the thymic lobes, and parallel reduction in size of the nodule and the rest of the thymus. Two patients were examined with magnetic resonance (MR) imaging. Sagittal MR images demonstrated continuity of the superior mediastinal nodule with the more caudal portion of the thymus. Recognition of this normal variant in children is important in order to avoid unnecessary mediastinal biopsies or overstaging of malignancies.