Imaging Findings

(A) Frontal chest radiograph demonstrates a large mass in the medial left hemithorax (arrow). There is loss of the left border of the heart, but the left hilar structures project through the mass (hilum overlay sign). (B) Lateral chest radiograph confirms the anterior location of the mass (arrows). (C) Contrast-enhanced computed tomography (CT; soft-tissue window) demonstrates a heterogeneous anterior mediastinal mass (arrow) that abuts the thymus.

  Differential Diagnosis