Variation of the Origins of the Phrenic and Long Thoracic Nerves – A Case Report

Introduction: In humans the phrenic nerve originates from the convergence of 3 individual nerve branches off the spinal roots of C3-C5, while the long thoracic nerve originates from the convergence of 3 branches off the spinal roots of C5-C7. However, a variation of the origins of these two nerves was found in a cadaver during dissection. Methods: This study of anatomical variation was conducted on an 86-year-old male cadaver provided for physical therapy students in a gross anatomy lab. Students and faculty members dissected the cadaver. The variations were identified when the neck and brachial areas were exposed for students to study. Results: On the left neck area, a short communicating nerve trunk is found connecting the beginning parts of both the cervical plexus and upper trunk of the brachial plexus. The phrenic nerve is the only branch off this communicating nerve and travels along the anterior surface of anterior scalene muscle. At the origin of this phrenic nerve, a small muscular branch divides and passes posteriorly to innervate the middle scalene muscle. On the right axillary area, the long thoracic nerve is found to branch off from the end of the posterior cord or initial part of the radial nerve of the brachial plexus and then travels distally and inferiorly to innervate the serratus anterior muscle. Conclusions: Findings of variation of the phrenic and long thoracic nerves in this study may provide additional information for clinicians to understand potential injury related to these two nerves. It is possible that an overstretch to the upper trunk of brachial plexus like with Erb-Duchenne palsy or a lesion to the posterior cord or initial portion of the radial nerve may cause involvement of injury to the phrenic and long thoracic nerves