An unusual case of accessory head of coracobrachialis muscle involving lateral cord of brachial plexus and its clinical significance

Abstract

Knowledge of anatomical variations in the peripheral nervous system is key in the interpretation of unusual clinical signs or during physical or diagnostic imaging. This case study is a description of an anatomical variation between the coracobrachialis muscle and brachial plexus. In a routine dissection in the human anatomy laboratory, we were faced with an anatomical variation in the coracobrachialis muscle, observed in the upper right limb of a male cadaver. The coracobrachialis muscle had a common origin at the apex of the coracoid process and then divided into two heads. The lateral head followed its normal course until insertion into the middle third of the humerus, while the medial head involved the lateral cord of the brachial plexus before insertion into the intermuscular septum in the proximal third of the humerus. Atypical anatomical variations have clinical andsurgical implications in procedures such as brachial plexus block and lateral cord compression. In these cases the result could be paralysis of the flexor musculature of the forearm and hypoesthesia of the forearm. (Folia Morphol 2017; 76, 4: 762-765)

Potential compression of the musculocutaneous, median and ulnar nerves by a very rare variant of the coracobrachialis longus muscle

“…The MCN can pierce or pass deep to the CRM [12,15,24,31,48]. It is believed that the CRM is the most common site of MCN entrapment and additional heads can place pressure on the MCN [4,14,16,17,27,32]. A potential site of MCN entrapment was also observed in the present case: at this point, 53.25 mm from its origin, the MCN (4.95 mm in diameter) passed under the CBL with the CRM being 21.95 mm in width and 3.19 mm.…”

“…Supracondylar process syndrome is one of the rarest types of median nerve neuropathy at about 0.5% [33,34]. Median nerve compression can also occur with the presence of a third head of the biceps brachii [53]; lastly, MN compression can occur more proximal in the arm, with additional heads of the CRM [13,31], and the additional head of the CRM causing compression of the lateral cord of the brachial plexus [16].…”

A proposal for a new classification of coracobrachialis muscle morphology

“…A number of authors have described variations in the CRM and MCN [2][3][4][5][6][7][8]. Most of these classifications are based on whether the MCN pierces CRM or not; however, that of Loukas et al [7] includes the relationship between the MCN, the median nerve (MN) and the CRM.…”

The co-occurrence of a four-headed coracobrachialis muscle, split coracoid process and tunnel for the median and musculocutaneous nerves: the potential clinical relevance of a very rare variation

“…Many earlier works describe the various types of morphological variations occurring within this muscle. Some relate to accessory slips of the muscle inserting to the medial epicondyle and medial supracondylar ridge of the humerus, medial intermuscular septum of the arm, others examine additional heads or bellies, while others relate to morphological variations in the proximal or distal attachment [ 3 , 15 – 17 , 21 , 25 , 31 ]. Morphological variations between CBM and MCN have also been noted, namely the nerve does not pierce the muscle [ 10 , 11 , 15 , 25 , 47 ].…”

“…The presence of additional bellies for the CBM may cause musculocutaneous or high median nerve paralysis [ 15 , 25 ].…”