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.