Surgical anatomy of the accessory phrenic nerve

Background. Reports place the frequency of phrenic nerve injury after cardiac operations between 10% and 85%, emphasizing the importance of an accurate anatomic description of the diaphragm's innervating nerves to reduce iatrogenic injury, length of hospitalization, and associated costs. The aim of our study was to explore the anatomic variations of the accessory phrenic nerve and relate these findings to phrenic nerve injury. Methods. Eighty adult formalin-fixed cadavers were dissected, resulting in 160 nerve specimens. Fifty nerve specimens were also examined laparoscopically with findings later confirmed through gross dissection. All nerves contributing to the phrenic nerve after crossing the anterior scalene were considered to be accessory phrenic nerves. Results. The phrenic nerve was present in all specimens, and 99 ( 61.8%) also had an accessory phrenic nerve. The accessory phrenic nerve arose from the nerve to subclavius in 60 specimens ( 60.6%), ansa cervicalis in 12 ( 12.1%), and nerve to sternohyoid in 7 ( 7%). The accessory phrenic nerve joined with the phrenic nerve in the thorax anterior to the subclavian vein in 45 ( 45.5%) specimens and posterior in 17 ( 22.2%). A phrenic-accessory phrenic nerve loop was found around the subclavian vein in 45 ( 35 on the right, 10 on the left) specimens and around the internal thoracic artery in 38 ( 31 on the right, 7 on the left). Conclusions. To reduce injuries to the diaphragm, the presence of an accessory phrenic nerve should be considered before mobilization and skeletonization of the internal thoracic artery above the second rib.