Where does the phrenic nerve exit the brachial (plexus)?

From the Guidelines

The phrenic nerve does not exit the brachial plexus. The phrenic nerve originates from the cervical plexus, specifically from the anterior rami of spinal nerves C3-C5, with the main contribution typically coming from C4. It descends through the neck, passing anterior to the anterior scalene muscle and posterior to the subclavian vein before entering the thorax. This nerve is anatomically distinct from the brachial plexus, which is formed by the anterior rami of spinal nerves C5-T1 and supplies the upper limb, as described in the study on plexopathy 1. The phrenic nerve's primary function is to innervate the diaphragm, providing both motor control for breathing and sensory innervation. Understanding this anatomical distinction is important for clinical procedures in the neck and thorax, as damage to the phrenic nerve can result in diaphragmatic paralysis and respiratory compromise. Key points to consider include:

• The brachial plexus is formed from the C5 to T1 ventral rami, and its structure and function are distinct from the phrenic nerve 1.
• The phrenic nerve's course through the neck and its relation to other anatomical structures are critical for avoiding injury during surgical or medical procedures.
• Clinical manifestations of phrenic nerve damage can include respiratory difficulties, which underscores the importance of preserving this nerve's function.

From the Research

Phrenic Nerve and Brachial Plexus Anatomy

• The phrenic nerve does not exit the brachial plexus, as it is not a part of the brachial plexus 2, 3, 4, 5, 6.
• The phrenic nerve is a separate nerve that arises from the cervical spine and descends through the thoracic cavity to innervate the diaphragm 5.
• The brachial plexus is a complex network of nerves that arises from the cervical spine and innervates the arm and shoulder region 2, 3, 4, 6.

Relationship Between Phrenic Nerve and Brachial Plexus

• The phrenic nerve can be injured in association with brachial plexus trauma, resulting in hemidiaphragmatic paralysis 3, 4.
• The incidence of phrenic nerve injury associated with brachial plexus trauma ranges from 10% to 20% 4.
• The phrenic nerve has been used as a donor nerve for neurotization in brachial plexus injuries, with variable results 5, 6.