Anatomical variations of brachial plexus: anomalous branching pattern

Abstract

INTRODUCTION Brachial plexus is a network of nerves which innervates the muscles of the back and the upper limb. It is formed by the ventral rami of C5, C6, C7, C8 and T1 spinal nerves. They are located behind Scalenus anterior and medius muscles of neck. Sometimes C4 roots joins with C5, when plexus is called prefixed type. On occasions T2 roots joins with T1 with disappearance of C4 roots; this forms the post-fixed type of plexus. The anterior divisions of the upper and middle trunks unite to form the lateral cord, and the anterior division of the inferior trunk continues as a medial cord. Ulnar nerve (C7, C8, and T1) is a branch of medial cord. In the axilla the ulnar nerve descends between the third part of axillary artery and axillary vein. The median nerve (MN) is formed by the union of lateral and medial roots from lateral and medial cord of BP respectively and both the roots were present lateral to the axillary artery. It then courses downwards in front of the arm. The ulnar nerve from the medial cord was found to be lateral to the axillary artery and then it crossed the axillary artery from lateral to medial and further it coursed down medial to the brachial artery. The musculocutaneous nerve arises from the lateral cord of the brachial plexus, passes inferolaterally and pierces coracobrachialis muscle before lying between biceps brachii and brachialis muscles. It was observed that ABSTRACT Background: The brachial plexus is the plexus of nerves formed by the anterior rami of lower four cervical and the first thoracic spinal nerves with little contribution of prefix C4 and postfix T2 spinal nerve. The variations in formation, location, and courses of the cords of brachial plexus and the median nerve are not uncommon and were studied in both axillae. Methods: The forty cadavers were studied preserved in the department of anatomy, SGRRIM and HS, Dehradun. The age and sex of the cadavers were not taken into consideration. The upper limbs were examined for the abnormal formation and union of branches of brachial plexus. Results: The musculocutaneous nerve communicates with the median nerve before and after piercing the coracobrachialis muscle. The lateral cord also gives the twig to the both roots of the median nerve. It also gives a branch which joined the ulnar nerve. The communication between medial root of median nerve and ulnar nerve also observed. Conclusions: Out of 20 examined cadavers (forty upper limbs), the variations in the formation and distribution of branches of the brachial plexus were noted in nine limbs (22.5%). The both sides of the brachial plexus were inspected and it was not found bilateral variations even in a single cadaver. The knowledge of these variations may be helpful for the anatomists, radiologists, anaesthetist, neurosurgeons and orthopaedic surgeons during surgical operation of the upper limb.