Variational anatomy of cervical part of phrenic nerve: An observational human cadaveric study

The phrenic nerve (PN) is not an exception to the variations. Recent cadaveric studies report that the third and fifth cervical nerves may be involved. The PN communicating branch might be considered as another option to neurotise the suprascapular nerve. The variants of the relationship between the subclavian vein and the PN should be familiar to anesthesiologists during subclavian vein cannulation to achieve a successful vein approach without causing PN palsy.

The study was carried out on both sides of 42 head and neck regions, which were obtained from the Department of Anatomy, KGMU, Lucknow. The study received Institutional Ethics Committee approval (Ref. code: XIV-PGTSC-IIA/P78).

Classical three root (C3,4,5), double root with varying contribution from C3 or C5 (C3,4/C4,5), and single root (C4/C5). Classical triple root PN formation was present in 57.68% of cases and was the most common pattern in our study population. The second most common (30.95%) formation was observed for the double root pattern (C4,5) by contribution of distal cervical segment (C5). Double root configuration of C3,4 was observed on 4.76% sides. Out of single root contribution incidence of C4 pattern was higher (4.76%) as compared to C5 (2,14%). One cadaver exhibited a dual C5 root with C4 on the right side in a male cadaver.

Although researchers have demonstrated that the PN nucleus extends locally from spinal cord segments C3 to C5, histological findings suggest that maximum contribution is derived from the C4 spinal nerve.