Anatomy and Clinical Significance of the Phrenic Nerve

Phrenic nerve - C3,4,5

Function:
Motor: Diaphragmatic contraction - breathing
Sensory: diaphragm, visceral pleura, pericardium, diaphragmatic peritoneum

Route in summary:
- Both run along scalenus anticus (anterior scalene)
- right phrenic passess anterior to brachiocephalic artery, posterior to subclavian vein, descending anterior to pulmonary hilum, anterior to R atrium, before passing through vena cava hiatus of the diaphragm at T8 level
- left phrenic passess anterior to the subclavian artery and posterior to brachiocephalic vein descending anterior to pulmonary hilum, anterior to L atrium

Clinical significance:
- Lung, cardiac, and gastrointestinal pathologies may result in referred pain to the shoulder C3,4,5 dermatomes
- Irritation of the phrenic nerve = hiccups

Examples:
Kehr's Sign: there are many explanations for kehr's sign. some are as specific as to associate it solely with splenic rupture (which it is considered a classical symptom of). However, any diaphramatic or peridiaphragmatic causes - cardiac, pulmonary, may potentially case the aforemented referred pain.