The phrenic nerve can also be damaged from blunt or penetrating trauma, metabolic diseases eg diabetes, infectious causes eg Lyme disease and herpes zoster, direct invasion by tumor, neurological diseases such eg cervical spondylosis and multiple sclerosis, myopathy and immunological disease (e.g., Guillain-Barre syndrome).The left phrenic nerve descends anteriorly between the pericardium and mediastinal pleura and can be injured while dissecting near the area of an internal thoracic artery. One common etiology of phrenic nerve injury is from surgery, primarily thoracic and cardiac surgery.Phrenic nerve palsy (also known as phrenic nerve paresis or paralysis) has many causes and can be caused by lesions anywhere along the course of the phrenic nerve, as it travels from the neck, to pierce the diaphragm adjacent to the pericardium. central parts of diaphragmatic pleura and peritoneum.diaphragm (except the most peripheral diaphragm, which is supplied by intercostal nerves).The phrenic nerve is the sole motor supply to each hemidiaphragm. On reaching the diaphragm, the terminal branches pierce the muscle and supply the central part of the peritoneum on its under aspect.(Image 2) Supply It passes in front of the root of the left lung and then descends over the left surface of the pericardium which separates the nerve from the left ventricle. It crosses the left side of the aortic arch and here crosses the left side of the left Vagus nerve. The left Phrenic nerve descends in the thorax along the left side of the left subclavian artery. Image 2 showing Right and Left Phrenic nerve supplying ipsilateral dome of the diaphragm

It then descends on the right side of the inferior vena cava to the diaphragm.Its terminal branches pass through the caval opening in the diaphragm to supply the central part of the peritoneum on its under aspect. It passes in front of the root of the right lung and runs along the right side of the pericardium, which separates the nerve from the right atrium. The right Phrenic nerve descends in the thorax along the right side of the right brachiocephalic vein and the superior vena cava. Both travel anterior to the hilum/bronchus on their respective side. The right and left phrenic nerves have a different course in the thorax but as a general rule they descend as lateral as possible whilst keeping in contact with the mediastinal pleura.

In the neck, the phrenic nerve lies on the anterior surface of the anterior scalene muscle, passes over the dome of the pleura and enters the thorax posterior to the subclavian vein. Thus, the phrenic nerve receives innervation from parts of both the cervical plexus and the brachial plexus of nerves. The phrenic nerve originates mainly from the 4th cervical nerve, but also receives contributions from the 3rd and 5th cervical nerves (C3-C5) in humans. Image 1 showing origin of the Phrenic Nerve

Nerve flossing neck diagrams