During median sternotomy and coronary artery bypass grafting, the left internal thoracic artery (LITA) is harvested as a conduit. The LITA runs in close proximity to which mediastinal structure that, if damaged, causes phrenic nerve palsy?

• A Vagus nerve descending posterior to the lung hilum
• B Thoracic duct crossing from right to left at T5 vertebral level
• C Left recurrent laryngeal nerve looping under the aortic arch
• D Phrenic nerve (C3, C4, C5) runs lateral to the internal thoracic artery on the pericardium, at risk during dissection of the lateral pericardium for LITA exposure ✓

Explanation

The phrenic nerve (C3, C4, C5) descends through the thorax on the fibrous pericardium, running along the lateral surface of the pericardium between the pericardium and the mediastinal pleura, just medial to (or alongside) the internal thoracic vessels. During LITA harvest, electrocautery or traction near the pericardium risks injury to the phrenic nerve, causing ipsilateral hemidiaphragm paralysis. Post-CABG phrenic nerve palsy is a recognised complication resulting in reduced pulmonary function. The vagus and recurrent laryngeal nerves are posterior structures not directly related to LITA harvest.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.