THE RECENT literature has had many discussions of the thymus and of thymic tumors. Although thymic tumors in general are not rare, malignant changes in undescended thymus tissue are.
The thymus gland is formed from the third and fourth branchial clefts, passes down the neck in front of, seldom behind, the left innominate artery, and enters the mediastinum during fetal life.1 At any position along this path of descent the entire gland or portions thereof may be left behind. Gilmour,2 in 1941, reported 13 cases showing thymic tissue at unusual positions. In one there was unilateral hyperplasia with complete absence of descent from the neck. The gland extended from the posterior border of the thyroid, inferiorly, to the bifurcation of the carotid artery, superiorly. Similar cases were described by Rossle (1932), Gruber (1920), and Harman (1921).*
Cooper,3 in 1832, reported the first case of thymic tumor, lymphosarcoma