A 52-year-old man undergoes cardiac surgery for coronary artery bypass grafting. Postoperatively, he develops a left-sided elevated hemidiaphragm on chest X-ray with reduced movement on fluoroscopy. Regarding the innervation of the diaphragm, all of the following are true EXCEPT:

Explanation

## Phrenic Nerve Anatomy and Diaphragmatic Innervation **Key Point:** The phrenic nerve is the primary motor nerve to the diaphragm, but its anatomical course and the location of diaphragmatic piercing are frequently tested and often confused. ### Correct Statements (Options 0, 2, 3) **Option 0 — Phrenic Nerve Origin:** - Arises from **C3, C4, C5** nerve roots (mnemonic: "C3, 4, 5 keeps the diaphragm alive") - This is the **sole motor innervation** to the diaphragm proper - Damage to these roots results in complete diaphragmatic paralysis on that side **Option 2 — Accessory Innervation:** - Lower intercostal nerves (T7–T12) provide **accessory motor innervation** to the peripheral muscular portions of the diaphragm - This is why some diaphragmatic function may persist even with phrenic nerve injury **Option 3 — Sensory Function:** - Phrenic nerve carries **sensory fibers** from parietal peritoneum, pericardium, and pleura - **Clinical Pearl:** Diaphragmatic irritation (e.g., subphrenic abscess, peritonitis) causes **referred shoulder pain** (Kehr sign) via phrenic sensory fibers to C3–C5 dermatomes ### Why Option 1 is Incorrect **High-Yield:** The phrenic nerve does **NOT** pierce the diaphragm through the **caval opening**. **Correct Anatomy:** - The **right phrenic nerve** pierces the **central tendon** and passes through the **caval opening** at T8 - The **left phrenic nerve** pierces the **muscular portion** of the left hemidiaphragm **directly** (NOT through the caval opening) - The esophageal hiatus (T10) transmits the esophagus and vagal trunks, not the phrenic nerve **Clinical Pearl:** In this patient's case, left phrenic nerve injury during cardiac surgery (common during internal mammary artery harvesting) causes left hemidiaphragmatic paralysis, explaining the elevated left hemidiaphragm and reduced movement on fluoroscopy. **Mnemonic:** **IVC at 8** — only the right phrenic passes through the caval opening; the left phrenic pierces the muscular diaphragm directly.