A 36-year-old woman presented with new-onset shortness of breath and chest wall discomfort.

She had a history of asthma and had delivered a healthy baby girl by cesarean section, five days prior. A chest radiograph was obtained that revealed a large right perihilar mass measuring 8.4 × 7.5 × 6.9 cm.

Chest computed tomographic (CT) imaging revealed right jugular vein and superior vena cava (SVC)thromboses and a large trans-spatial hypervascular superior mediastinal mass with extensive lobular soft tissue densities measuring 12.2 × 8.0 × 10.8 cm that partially encircled the SVC and extended toward the perihepatic space.

The patient was started on a heparin drip for treatment of thrombi and admitted to the hospital. The initial differential diagnosis included metastatic gestational trophoblastic disease and vascular malformation.

Chest CT venography revealed filling defects to the large mediastinal mass and the presence of a right lower lobe pulmonary embolism. Cardiothoracic surgery was consulted and recommended magnetic resonance imaging of the chest and abdomen.