Thymus

Structure

The thymus is comprised of two lobes that meet in the upper midline. In children, it is pinkish-brown with a lobulated surface, while in adults it is gradually replaced by fat tissue.

Key Features & Anatomical Relations

The thymus is located posterior to the manubrium of the sternum and anterior to the pericardium. It is laterally bounded by the anterior border of the superior lobe of each lung. Superiorly, it peaks into the superior thoracic aperture and inferiorly it is bounded by the pericardium. The inferior limits of the thymus extend to the end of the sternal angle (angle of Louis).

Function

The thymus is responsible for the production of T-cells by maturation of thymocytes. A supply of T-lymphocytes is established before puberty making the organ redundant in later life, thus it degenerates and is replaced by fat.

Arterial Supply

The thymus receives its arterial supply from branches of internal thoracic, inferior thyroid, and sometimes the superior thyroid arteries.

Venous Drainage

Thymic veins drain the thymus into the internal thoracic, inferior thyroid, and the left brachiocephalic veins.

Nerve Supply

The thymus receives innervation from divisions of the vagus nerve and the cervical sympathetic chain via the cervicothoracic ganglion, though the function of innervation to the gland is not well understood aside from vasomotor functions.

Lymphatic Drainage

Efferent lymphatics from the thymus drain into brachiocephalic, tracheobronchial, and parasternal lymph nodes.

List of Clinical Correlates

—Thymoma

—Myasthenia Gravis