Toddler with respiratory distress

CXR and CT of lymphatic malformation of the thymus
CXR AP obtained intially (left) shows a normal appearing exam with a normal appearing thymus. CXR AP obtained 10 days later for continued respiratory distress (right) showed interval development of an anterior mediastinal mass. Axial+coronal CT with contrast of the chest shows a large low density anterior mediastinal mass with multiple thin septations.

The diagnosis was lymphatic malformation of the thymus which had bled in the interval between the two exams.