Case report Acta Medica Academica 2016;45(2):163-168 DOI: 10.5644/ama2006-124.173 Accessory coracobrachialis muscle with two bellies and abnormal insertion - case report George Paraskevas, Konstantinos Koutsouflianiotis, Kalliopi Iliou, Theodosis Bitsis, Panagiotis Kitsoulis Department of Anatomy, Faculty Objective. In the current study a brief review is presented of the cora- of Medicine, Aristotle University of cobrachialis muscle’s morphological variability, action, embryological Thessaloniki, Thessaloniki, Greece development and clinical significance. Case report. We report a case of a left-sided coracobrachialis muscle consisting of two bellies. The deep belly inserts into the usual site in the middle area of the antero- Correspondence: medial aspect of the left humerus, whereas the superficial belly inserts [email protected] through a muscular slip into the brachial fascia and the medial in- Tel.: + 302 310 999 330 termuscular septum, forming a musculo-aponeurotic tunnel in the Fax.: +302 310 819 831 middle region of the left arm, for the passage of the median nerve, brachial artery and veins, medial antebrachial cutaneous nerve and ulnar nerve. Conclusion. Awareness of such a muscle variant should Received: 1 June 2016 be kept in mind by physicians and surgeons during interpretation of Accepted: 26 October 2016 neural and vascular disorders of the upper limb, since such a variant may potentially lead to entrapment neuropathy and/or vascular com- pression, predisposing to neurovascular disorders, as well as during Key words: Coracobrachialis muscle ■ preparation of that muscle in cases of utilizing it as a graft in recon- Variation ■ Clinical applications. struction of defects. Introduction variable anatomical sites, such as the surgi- cal neck of the humerus (3), the tendon of The coracobrachialis muscle (CBM) is a the latissimus dorsi (4), the medial head of widely known muscle of the anterior com- the triceps (5), the brachial fascia (6), the partment of the arm that has received little medial epicondyle of the humerus or the an- attention from anatomists and clinicians, tebrachial fascia (7). due to its minor importance for the forward However, the presence of a variant CBM flexion of the arm. However, the CBM has recently received greater surgical signifi- type, as the finding of the current study, cance since it is utilized as a graft in recon- where its superficial portion participates structive surgery after mastectomy, in the in the formation of a musculo-aponeurotic treatment of defects of the axillary and in- tunnel including median, ulnar nerves, as fraclavicular area (1), or in therapy for long well the brachial vessels, has not been de- standing facial palsy (2). Apart from the tected so frequently. This type of CBM mus- CBM’s usual insertion site into the median cular slip could under circumstances such portion of the antero-medial aspect of the as hypertrophy, hematoma or strong CBM humerus, the muscle may also insert into contraction under resistance, predispose to 163 Copyright © 2016 by the Academy of Sciences and Arts of Bosnia and Herzegovina. Acta Medica Academica 2016;45:163-168 median and/or ulnar neuropathy, as well as Case report to vascular disorders. In the current study a brief review of the During routine educational dissection an ab- CBM’s morphological variability, action, normal CBM was detected in an adult male embryological development and clinical sig- cadaver, aged 78 years old, on the left side. In nificance is presented. particular, after meticulous preparation and SH DM DH * 1 2 3 BF Figure 1 An accessory coracobrachialis muscle on the anterior aspect of the left arm is shown, composed of a superficial head (SH) and deep head (DH). The SH terminates into a muscular slip (asterisk) that inserts into the brachial fascia (BF). The musculo-aponeurotic channel formed in that way contains the nerves and vessels of the medial bicipital groove of the arm (1: brachial artery, 2: median nerve, 3: medial antebrachial cutaneous nerve, DM: deltoid muscle). 164 George Paraskevas et al. : Accessory coracobrachialis muscle dissection of the skin and the underlying per or short portion is the smallest, originat- fascia of the left arm region, we came across ing from the coracoid process and inserted a bicipital CBM, consisting of a superficial into the shoulder joint capsule. This portion and a deep belly originating together from was termed by Wood the “coracobrachialis the tip of the coracoid process. The deep superior or brevis or rotator humeri”. The belly terminated via a musculo-aponeurotic lower or long portion is inserted into the tendon into its usual insertion site, that is internal condyloid ridge, the internal inter- the middle area of the antero-medial aspect muscular septum or the trochlea, and was of the left humerus. The superficial belly -ter termed by Wood the “coracobrachialis lon- minated through a muscular slip into the gus”. The middle portion of the muscle is the brachial fascia and the medial intermuscu- largest and is inserted into the middle of the lar septum. The latter muscular slip formed inner surface of the humerus. This portion a musculo-aponeurotic channel in the mid- of the CBM was termed the “coracobrachia- dle region of the left arm for the passage of lis proprius or medius” by Wood (9). Wood the median nerve, brachial artery and veins, considered that the middle portion is usu- the medial antebrachial cutaneous nerve ally found in human subjects (9), however and the ulnar nerve (Figure 1). It should be other authors speculated that the middle noted that the CMB on the right side did not and lower portions are fused, trapping the display any morphological variations. The musculocutaneous nerve between them (4, cadaver was fixed by formalin and alcohol 6). However, there are instances (3.5-6.5%) solution. The cause of death was unrelated in which the CBM is not traversed by the to the current study, whereas no other varia- musculocutaneous nerve (4). Mori observed tions, pathological conditions or evidence of in 6% of cases that the course of the muscu- previous surgical procedures were present in locutaneous nerve is on the ventral surface the arm. The morphology and topographic of the CBM (11). relationship of the current variant were re- Apart from Wood’s classification system corded with repeated photographs. of the CBM’s morphology and attachment sites, in 1964 Mori mentioned the existence Discussion of the CBM’s separation into superficial and deep layers. In particular, in 16% of cases As is widely known, the CBM originates the CBM’s belly was completely separated, from the apex of the coracoid process, along whereas in 8% it was incompletely separated with the tendon of the short head of the bi- into a superficial and a deep layer (11). In ceps, and by muscular fibers from the proxi- our case, the CBM displays two muscular mal part of that tendon. The CBM terminates heads, one superficial and one deep. The in an impression, midway across the medial deep head is inserted into the medial as- border of the humeral shaft (8). However, pect of the humerus as usual, whereas the the CBM’s origin and its insertion display superficial head terminates through a mus- great variability. As regards the CBM’s inser- cular slip into an aponeurotic lamina, which tion, which is the case in the current study, blends into the brachial fascia and the me- it may be located in various anatomical sites, dial intermuscular septum. The latter head from the shoulder joint capsule to the me- of the CBM creates a fibro-muscular tunnel dial epicondyle, the olecranon process or the for the passage of the vessels and nerves of antebrachial fascia (7, 9, 10). the medial bicipital groove of the arm. This As long ago as in 1867, John Wood de- variant resembles that mentioned by Ray et scribed three portions of the CBM. The up- al. where two CBM bellies were displayed, 165 Acta Medica Academica 2016;45:163-168 with the superficial one inserted into the derm. In order for a certain muscle to be brachial fascia (6). Our case differs from this formed, muscle primordia are fused. Some in that the deep CBM head is musculo-apo- muscle primordia disappear through cell neurotic, whereas the deep belly in Ray et al. death. The persistence of some cells between was totally muscular. Furthermore, the cur- the CBM and the biceps brachialis muscle rent finding resembles the abnormal muscle may result in an accessory CBM belly (1, observed by Paraskevas et al. that originated 14). Alternatively, someone could hypoth- from the CBM and the tendon of the long esize that during the CBM’s embryological head of the biceps brachii, and inserted into development, a combination occurs of the the medial intermuscular septum and the CBM’s tangential splitting into two heads brachial fascia, forming a musculo-aponeu- and migration of the CBM’s superficial head rotic channel for the passage of the nerves into more distal and medial region (16). As and vessels of the arm (12). We suggest that regards the CBM’s action, the muscle flexes our abnormal muscle consists of a superfi- the arm forward and medially, especially cial layer of the CBM corresponding to the from a position of brachial extension (8). CBM’s lower portion. The CBM, according to Wood, resembles Some cases of additional CBM heads the triceps adductor femoris. In particular, have been reported in the relevant literature. the short upper portion of the muscle cor- Chouke noted an accessory CBM head aris- responds to the adductor brevis, the middle ing from the conoid ligament of the clavicle, portion to the adductor longus and the long blending with the main CBM and inserting lower portion of the CBM to the adductor into the medial intermuscular septum (13).