Posterior Mediastinum - LO 5

5. Describe the courses and major branches of the vagus nerves (CN X) in the thorax.

Recall that the vagus n. (CN X) descends the neck, packaged in the carotid sheath, posterior to the internal jugular v. and common carotid a. At the root of the neck, the vagus n. (as well as superior and inferior cervical cardiac branches, which arise from the vagus in the carotid sheath) emerges from the carotid sheath as it enters the thoracic inlet (superior thoracic aperture).

Right vagus n.

• • The right vagus n. enters the thorax via the superior mediastinum, medial to the phrenic n., and anterior to the subclavian a. Once inside the thorax, the right recurrent laryngeal n. branches from the vagus n., and wraps posteriorly around the right subclavian a. before ascending out of the thorax to the larynx. The right vagus n. descends lateral (right) to the trachea, passing posterior to the root of the right lung. Posterior to the root of the lung, the right vagus supplies bronchial brs. (pre-ganglionic parasympathetic) to the right pulmonary plexus. The right vagus n. further descends the posterior mediastinum, providing branches to the esophageal plexus, while moving to the posterior aspect of the esophagus where it is joined with branches from the left vagus n. to become the posterior vagal trunk. The posterior vagal trunk exits the thorax through the esophageal hiatus (near T10), enters the abdominal cavity, and becomes the major supplier of parasympathetics to the foregut and midgut.

Left vagus n.

• • The left vagus n. enters the thorax via the superior mediastinum, medial to the phrenic n., and anterior to the subclavian a. Once inside the thorax, the left vagus n. descends anterior to the arch of the aorta, and spawns the left recurrent laryngeal n., which wraps posteriorly around the concavity of the arch in the vicinity of the ligamentum arteriosum before ascending out of the thorax to the larynx. The left vagus n. descends posterior to the root of the left lung, supplying bronchial brs. (pre-ganglionic parasympathetic) to the left pulmonary plexus. The left vagus n. further descends the posterior mediastinum, providing branches to the esophageal plexus, while moving to the anterior aspect of the esophagus where it is joined with branches from the right vagus n. to become the anterior vagal trunk. The anterior vagal trunk exits the thorax through the esophageal hiatus (near T10), enters the abdominal cavity, and becomes a minor supplier of parasympathetics to the foregut.

A mnemonic to help remember which vagus n. forms the bulk of which vagal trunk is LARP (left anterior, right posterior).