The aberrantly positioned thymus. A cause of mediastinal or neck masses in children

Three cases are reported in which the thymus gland was anomalously positioned, leading to confusion with pathologic mediastinal or neck masses. In one patient the thymus was lodged between the superior vena cava and ascending aorta and impinged upon the right mainstem bronchus, producing obstructive emphysema of the right middle lobe and right lower lobe. In another patient the thymus displaced the trachea anteriorly and the esophagus to the left. An incompletely descended thymus in the remaining child presented as a substernal mass which enlarged during expiration or when intrathoracic pressure was increased. A diagnostic trial of adrenocorticosteroids can be employed to help distinguish aberrantly positioned thymus from other mediastinal masses.