Mediastinal mass and tracheal compression due to an aneurysm of a systemic-to-pulmonary collateral artery in a patient with pseudotruncus arteriosus

A patient with pseudotruncus arteriosus who presented with a large mediastinal mass due to a systemic to pulmonary collateral artery aneurysm is reported. This aneurysm caused tracheal compression with resulting dyspnea and postobstructive pneumonitis, which are unusual presenting features in these patients. The differential diagnosis for a mediastinal mass arising in a patient with pseudotruncus arteriosus, or any other patient with possible systemic-to-pulmonary collateral arteries, should include aneurysm.