Persistent Enlarged Thymus in an Adult Human Cadaver

Thymus is an irregular bilobed gland situated in the superior and anterior mediastinum. It lies above the pericardium, aortic arch, left brachiocephalic vein, and trachea. Superiorly thymus may extend to the lower pole of thyroid gland and inferiorly up to the diaphragm.. Each thymic lobe is covered by a fibrous capsule. It weighs about 10 to 15 gms at birth and progressively increases in size and weighs about 20 to 30 gms at puberty. There after it undergoes involution and is converted into a fibrofatty mass. Thymus does show morphological variations in the gross anatomy. It may be persistent in the adult. This fact is clinically important for radiologists to make a differential diagnosis in case of a mediastinal mass. A thorough knowledge of the embryology and anatomy of the thymus, normal variations and ectopic locations of thymus and its dynamic changes is necessary before doing any invasive procedure.