The phrenic nerve is the sole motor supply to the diaphragm, making it the most vital peripheral nerve in the body. Its long thoracic course from the neck to the diaphragm makes it vulnerable to cervical spine injury, thoracic surgery, tumours, and cardiac procedures. Unilateral phrenic nerve palsy is tolerated with mild dyspnoea in otherwise healthy individuals, but bilateral palsy produces respiratory failure requiring ventilatory support.
| Origin | Cervical plexus primarily from C4 with contributions from C3 and C5 |
|---|---|
| Course | Descends on the anterior surface of the anterior scalene through the thorax to the diaphragm, the right nerve passing anterior to the lung root and the left passing anterior to the aortic arch |
| Motor | |
| Sensory |
|
Phrenic nerve injury during cardiac surgery, lung resection, or central venous line placement produces ipsilateral hemidiaphragm paralysis, visible on chest radiograph as an elevated hemidiaphragm. In infants with congenital diaphragmatic eventration, phrenic nerve function must be assessed to guide surgical management. Referred pain from diaphragmatic irritation (subphrenic abscess, hepatic pathology) travels via the phrenic nerve to produce shoulder tip pain, one of the classic referred pain patterns in clinical medicine.
Hemidiaphragm paralysis from phrenic nerve injury during thoracic or cervical surgery producing elevated hemidiaphragm on chest radiograph and dyspnoea on exertion, with recovery depending on the mechanism of injury.
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