Anatomic variations of the phrenic nerve at the superior thoracic aperture (thoracic inlet): Implications for the cardiothoracic surgeon

Routine use of the internal thoracic (mammary) artery (ITA) in coronary revascularization has prompted surgeons to seek ways to increase its length and mobility while avoiding phrenic‐nerve (PN)injury related to dissection of the ITA to its origin. Because no clear anatomic description of the PN/ITA relationship exists, we investigated the course of the PN through the superior thoracic aperture (thoracic inlet) and its proximity to the origin of the ITA in 51 cadavers. The ITA coursed posterior to anterior as it crossed the subclavian vein and the PN, passing between the subclavian artery and vein, was lateral to the origin of the ITA (100%). The superior/inferior position of the PN to the ITA is variable. The PN passed superior and medial to the ITA (66%) but was not consistent from side to side in the same cadaver. The PN passed lateral and inferior to the IMA in the right hemithorax (27%) and in the left (40%). A bilateral superior/medial relationship was found in 50% of cadavers and a bilateral inferior/lateral one in 20%. The surgical implications of this anatomic finding are that the PN is vulnerable to injury when it is inferior to the ITA as it passes from lateral to medial through the superior thoracic aperture (thoracic inlet) and ITA dissection is carried past the posterior border of the subclavian vein; 1 cm of soft tissue will protect the PN if dissection ends at the anterior border of the vein.