During dissection of the left lung hilum in a patient undergoing lobectomy, the surgeon identifies a nerve crossing immediately anterior to the root of the lung and another passing posterior to it. Which pair is correct?

• A Phrenic nerve anteriorly, vagus nerve posteriorly ✓
• B Vagus nerve anteriorly, phrenic nerve posteriorly
• C Phrenic nerve anteriorly, sympathetic trunk posteriorly
• D Recurrent laryngeal nerve anteriorly, phrenic nerve posteriorly

Explanation

On both sides, the phrenic nerve descends on the anterior surface of the lung root within the fibrous pericardium to reach the diaphragm, while the vagus nerve passes posterior to the root and contributes to the esophageal plexus. A traditional mnemonic places the phrenic nerve 'on' the root and the vagus 'behind' it. The recurrent laryngeal nerves do not relate to the lung roots.

Reference: Gray's Anatomy for Students, 4th ed.

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Written and medically reviewed by the StethoPrep medical team.