Phrenic Nerve

Description

Arising chiefly from the anterior rami of C3 to C5, the phrenic nerve descends on the anterior surface of the anterior scalene muscle in the lateral neck, deep to the prevertebral fascia and lateral to the carotid sheath. Inferiorly it courses posterior to the sternocleidomastoid, then passes between the subclavian artery and subclavian vein at the root of the neck to enter the thorax. Along this pathway you would expect to see the nerve’s close relationship to the internal jugular vein and common carotid artery medially, the brachial plexus trunks posterolaterally, and the transverse cervical and suprascapular vessels crossing the posterior triangle. Small nodal groups in the deep cervical chain may be indicated. A tight corridor. Phrenic nerve anatomy matters because small positional differences change surgical risk: during anterior scalene blocks, central venous access, or supraclavicular approaches, the nerve’s course on the scalene explains why hemidiaphragmatic paresis can follow regional anesthesia and why inadvertent injury produces dyspnea with paradoxical diaphragmatic motion. The thoracic segment also frames the classic teaching point that the phrenic travels with the fibrous pericardium to the diaphragm, so pericarditis can refer pain to the shoulder via C3 to C5 dermatomes. For thoracic surgeons, it is also the landmark to protect during mediastinal dissection and cardiac procedures. Use this illustration for gross anatomy and neuroanatomy teaching when you need a clean explanation of cervical plexus contributions, scalene relationships, and the nerve’s transition from neck to thorax, as well as for anesthesia and surgery texts discussing interscalene block complications or phrenic nerve palsy. It also fits patient education materials on diaphragmatic paralysis and postoperative respiratory symptoms in male anatomy. Anatomical accuracy verified by SciePro's Medical Advisory Board.