Abstract
Purpose
The study report describes a rare bilateral variant of a six- and five-headed coracobrachialis muscle (CB). The musculocutaneous nerve (MCN) (bilaterally) and the median nerve (MN) lateral root (unilaterally) pierced CB heads, separating superficial from deep heads.
Methods
The variant bilateral CB was identified in a 78-year-old formalin-embalmed male cadaver, derived from a body donation program after a signed informed consent.
Results
At the right side: The 6-headed CB was pierced by the MCN, while the MN lateral root pierced the one superficial and deep head. CB was supplied by the lateral cord and the MCN. At the left side: A 5-headed CB was identified with three superficial distinct origins that fused into a common superficial head coursing anterior to MCN. The variant CB bilaterally (with 11 heads in total) coexisted with a MN variant formation, an atypical course of the MN lateral root through CB (right side), a connection of the MN lateral root with the MCN (left side) and a variant axillary artery branching pattern (bilaterally).
Conclusions
Course and direction of the accessory CB heads may occasionally entrap the MCN and/or adjacent structures (brachial artery and MN). The MCN compression results in problems in the glenohumeral joint flexion and adduction, and tingling or numbness of the elbow joint, the forearm lateral parts and the hand.
Similar content being viewed by others
Avoid common mistakes on your manuscript.
Introduction
Coracobrachialis muscle (CB), the smallest flexor of the anterior arm compartment, originates from the coracoid process and inserts medially, into the middle third of the humeral shaft. It is innervated by the musculocutaneous nerve (MCN), piercing the muscle heads, distinguishing the superficial from the deep heads [19], and is supplied by the brachial artery (BA) [20]. Koizumi [8, 9] demonstrated that the CB is composed of a superficial belly supplied by the lateral cord of the brachial plexus and a deep belly supplied by the MCN. The CB commonest morphological variant is the presence of one accessory head, while multiple accessory heads are quite unusual [19]. Occasional CB descriptions are referred to four [18] or even six [21] heads and different distal attachments [19]. The CB may also have accessory bundles inserting into the medial intermuscular septum, the medial epicondyle, the flexor carpi radialis, the brachialis, the brachioradialis or the pronator teres muscles [15]. Other variants include the CB longus, the CB brevis [16] and the coraco-capsularis muscle [20]. Course and direction of these accessory structures may occasionally entrap the median nerve (MN) and/or the BA [5]. The MCN may be compressed between CB heads [17, 19] leading to weakness of the anterior arm muscles and problems in the glenohumeral joint flexion and adduction. Tingling or numbness may occur, as the MCN provides sensory innervation to the elbow joint, the forearm lateral part, and the hand [18]. The current report describes a rare bilateral variant of a six- and five-headed CB originated from the coracoid process and the tendon of the biceps brachii (BB) short head. All heads are inserted into the medial surface of the humerus middle third. The MCN (bilaterally) and the MN lateral root (unilaterally) were piercing the CB heads, separating superficial from deep heads. Coexisted variants were also described. The systematic knowledge on the potential clinical consequences of such a rare bilateral finding is also discussed.
Case report
During the axillae and arms dissection of a formalin-fixed 78-year-old Greek male donated cadaver, a quite rare CB bilateral variant was detected. The cadaver was donated to the Anatomy Department of the Medical School of the National and Kapodistrian University of Athens, through the “Anatomical Gift Program” after written informed consent. The atypical CB had multiple accessory heads, bilaterally. The right-sided six-headed CB had three superficial (1, 2, and 3) and three deep heads (4, 5, and 6). All heads were pierced by the MCN, and the MN lateral root pierced heads 1, 4, 5, and 6. It seems that the CB was triplicated. The head 1 arose from the coracoid process tip, the heads 2 and 3, as well as the heads 4, 5, and 6 originated from the tendon of the BB short head. The heads 4 and 5 joined and before their insertion were fused with the head 1. The head 2 inserted into the middle third of the humeral shaft, after receiving a bundle from the head 3. The whole complex is inserted into the middle third of the humeral shaft. The six-headed CB was supplied by four branches of the lateral cord and from the MCN. The lateral cord penetrated CB and gave off the MCN and the MN lateral root, more distally than usual. The MCN passed between CB superficial and deep heads (Fig. 1A). At the contralateral side, a five-headed CB was identified. The CB had three superficial distinct origins that fused into a common superficial head coursing anterior to the MCN. The superficial heads 1 and 2 emanated from the coracoid process and joined. The superficial head 3 that originated from the tendon of the BB short head joined the superficial heads (1 and 2) complex and was commonly inserted medially, into the middle humeral third. The deep head 4 originated from the coracoid process base and joined the deep head, originating from the shoulder joint capsule. The deep heads 4 and 5 in common inserted into the medial humeral shaft, just above the common insertion of superficial heads (1, 2 and 3) (Fig. 1B). The variant CB coexisted with an MN variant formation, an atypical course of the MN lateral root through CB (right side), a connection of the MN lateral root with the MCN (left side) and a variant axillary artery (AA) branching pattern (bilaterally).
Brachial plexus branches’ atypical formation, course, and other variants
At the right side, the MN was formed distally, at the lower border of the latissimus dorsi muscle tendon, after the asymmetrical union of the lateral and medial roots (Fig. 2A). The medial cord was subdivided at a proximal level in relation to the lateral cord division. The four intercostobrachial nerves (branches of the 2nd, 3rd, 4th, and 5th intercostal nerves) coursed anterior to the long thoracic nerve. On the left side, a connecting branch of the MCN to the MN lateral root was identified (Fig. 2B).
The axillary artery atypical branching pattern
At the right side, three LTAs (LTA1, LTA2 and LTA3) and an abnormal trunk were identified. The LTA1 emanated from the AA 1st part. The abnormal trunk, posterior to pectoralis minor muscle, gave off the LTA2, the thoracoacromial artery (TAA) and the subscapular artery that, 23.82 mm distally, divided into the LTA3, a branch for the subscapularis’ upper part and the thoracodorsal artery. The circumflex scapular artery and a trunk for the teres major and minor supply emanated from the AA 3rd part, 4.1 cm distally (Fig. 2A).
On the left side, a symmetrical LTA triplication and an abnormal trunk were identified. Superior thoracic artery was absent, and at the 3rd rib inferior border, the AA gave off the LTA1 and 0.5 cm below, the common trunk (TAA-2nd LTA and 3 pectoral branches for the pectoralis major and minor supply). The subscapular artery arose medial to the TAA and gave off an upper branch for the subscapularis superior portion supply, the LTA3, the circumflex scapular artery, a branch for the teres major and the thoracodorsal artery (Fig. 2B). Overall cadaver status was without obesity or muscle atrophy. No signs of pathological conditions, trauma, or earlier surgery in the cadaver’s upper limbs were identified.
Discussion
The cadaveric report describes a bilateral quite rare variant of a six- and five-headed CB with attachment on the medial surface of the humeral shaft. Szewczyk et al. [19] recorded two accessory CB heads in 7.9% and Olewnik et al. [18] found three accessory heads innervated by the MCN. Occasional CB descriptions with four [18] or even six [21] heads and different distal attachments [19] exist.
In the current report, the occurrence of such a bilateral complex structure is associated with developmental alterations. The aberrant muscle formations may be remnants of muscle primordia from different layers that failed to disappear or fuse to form a single muscle [3, 10]. Some of the brachial plexus fibers may follow an aberrant course, due to failure in differentiation. In the first stage, the flexor arm muscles are tightly connected in a pre-muscle mass. The three muscles become distinct structures when the embryo reaches a length of 14–16 mm. Probably, the CB additional heads are formed during this stage or later (at an embryonal length 11–19 mm) when the single mass divides into smaller parts recognized as CB supernumerary heads [1].
Due to CB high morphological variability, there is a possibility to identify new variants not previously described. CB accessory heads have also been associated with MCN variants. The MCN atypical course shows a wide variability [4, 14]. The MCN may not pierce CB (16.67%) [7]. The CB accessory heads may be combined with multiple neurovascular variants, as in the current case where triple LTAs were bilaterally and four intercostobrachial nerves were unilaterally detected. The rare occurrence of multiple LTAs (3.09%) is clinically significant [13]. Particularly the LTA and thoracodorsal artery points of origin [12] are important, since the arteries should remain intact during neck and breast surgery [13]. Concerning the intercostobrachial nerve, it should be preserved during the radical mastectomy to prevent sensory loss or dysesthesia in the upper arm area. Thus, its identification and possible variations, such as duplication, triplication and multiplication with their possible interconnections are quite important [11].
The presence of additional CB heads may have clinical implications, since the supernumerary head (s) may compress the MCN, especially when this nerve courses between two bellies [17, 19]. The MCN entrapment may complicate the glenohumeral joint flexion and adduction and cause tingling or numbness, as the MCN provides sensory innervation to the elbow joint, the forearm lateral parts and hand [17]. Entrapment at this level is extremely rare, but it may arise as a major issue, since both the anterior arm compartment and the forearm muscles may be affected leading to disabilities. Detailed imaging of the area with magnetic resonance imaging should be performed prior surgery, to evaluate the area variants, since such cases are extremely rare. Furthermore, shoulder surgery including osteotomy and coracoid process transfer in Bristow- Latarjet procedure, subcoracoid loops and muscle transfers requires muscles’ mobilization that are attached to the coracoid process [2]. Therefore, data concerning the level of MCN penetration into the CB will shed light on such surgical procedures, thus avoiding MCN iatrogenic lesions [4]. Intraoperative blunt trauma or elongation of MCN may lead to neurapraxia, therefore detailed planning of the procedure and the variants through preoperative imaging are of utmost importance for avoiding such complications.
CB has a definite clinical significance. During brachial plexus blockade, the CB serves as guide for AA identification [7]. It is well vascularized and represents a good choice as a transplant for treating long-standing facial palsy [3], as a graft for post-mastectomy reconstruction, and in both axillary and infraclavicular deformities [3]. In some cases, an accessory CB can lead to subcoracoid impingement and MCN, MN, or ulnar nerve palsy due to hypertrophy, injury, or brachial artery compression. Variant CB could also cause confusion during surgery and imaging evaluation [6]. The MCN atypical course would be of considerable value during axillary blocks and flap dissections, as well as in identifying and treating post-traumatic peripheral neuropathies and reconstructive nerve grafting following brachial plexus injury, coracoid process grafting and shoulder arthroplasty. Knowledge of the morphological variants of the shoulder area, prior to surgery, is crucial since many variants have also been reported at the acromion and the scapula. Thorough preoperative planning may minimize intraoperative “surprises” and, hence, complications.
Study limitations
As the medical history of the dead man was unknown, the clinical impact of the identified variants could not be estimated. However, we believe that physicians and surgeons should be alert for the possible presence of such variants, because their occurrence may have clinical significance, as it was previously highlighted.
Conclusions
To the best of our knowledge, such a combination of muscular and neurovascular variants has not been reported. The quite rare CB variant with multiple heads (11 in the number, 6 om the right and 5 on the left side) was identified bilaterally. The superficial heads were separated from the deep heads of the muscle complex by the MCN course. The six-headed CB was supplied by the lateral cord and the MCN. The variant CB coexisted with a MN variant formation, an atypical course of the MN lateral root through CB (right side), a connection of the lateral root with the MCN (left side) and a variant AA branching pattern (bilaterally) (with focus on LTA triplication and abnormal arterial trunks'formation) and an intercostobrachial nerve quadrupling.
Data availability
Data and material related to the report will be available with the corresponding author for further reference.
Abbreviations
- CB:
-
Coracobrachialis muscle
- MCN:
-
Musculocutaneous nerve
- MN:
-
Median nerve
- BA:
-
Brachial artery
- BB:
-
Biceps brachii muscle
- LTA:
-
Lateral thoracic artery
- TAA:
-
Thoracoacromial artery
References
Bardeen C (1905) Studies of the development of the human skeleton. Am J Anat 4:265–302
Clavert P, Lutz JC, Wolfram-Gabel R et al (2009) Relationship of musculocutaneous nerve and the coracobrachialis during coracoids abutment procedure (Latarjet procedure). Surg Radiol Anat 31:49–53
El-Naggar MM, Al-Saggaf S (2004) Variant of the coracobrachialis muscle with a tunnel for the median nerve and brachial artery. Clin Anat 17(2):139–143
Flatow EL, Bigliani LU, April EW (1989) An anatomic study of the musculocutaneous nerve and its relationship to the coracoid process. Clin Orthop 244:166–171
Garbelotti SA, Marques SR, Rocha PR et al (2017) An unusual case of accessory head of coracobrachialis muscle involving lateral cord of brachial plexus and its clinical significance. Folia Morphol 76(4):762–765
Georgiev GP, Tubbs RS, Landzhov B (2018) Coracobrachialis longus muscle: humeroepitrochlearis. Cureus 10(5):e2615
Ilayperuma I, Nanayakkara BG, Hasan R, Uluwitiya SM, Palahepitiya KN (2016) Coracobrachialis muscle: morphology, morphometry and gender differences. Surg Radiol Anat 38(3):335–340
Koizumi M (1989) A morphological study on the coracobrachialis muscle. Acta Anat Nippon 64:18–35
Koizumi M, Sakai T (1995) The nerve supply to coracobrachialis in apes. J Anat 186:395–403
Kopuz C, Icten N, Yildirim M (2002) A rare accessory coracobrachialis muscle: a review of the literature. Surg Radiol Anat 24:406–410
Kumar PA, Reddy KRD, Bapuji P (2014) Multiple intercostobrachial nerves. JEMDS 3(57):12978–12984
Natsis K, Totlis T, Tsikaras P, Skandalakis P (2006) Bilateral accessory thoracodorsal artery. Ann Anat 188(5):447–449
Loukas M, Louis RG Jr, Wartmann CT (2006) Superficial lateral thoracic artery. Ann Plast Surg 57(4):475–476
Loukas M, Aqueelah H (2005) Musculocutaneous and median nerve connections within, proximal and distal to the coracobrachialis muscle. Folia Morphol 64:101–108
Nakatani T, Tanaka S, Mizukami S (1998) Bilateral four-headed biceps brachii muscles: the median nerve and brachial artery passing through a tunnel formed by a muscle slip from the accessory head. Clin Anat 11(3):209–212
Olewnik Ł, Zielinska N, Gołek Ł, Aragonés P, Sanudo JR (2021) Is it the coracobrachialis superior muscle or is it an unidentified rare variant of coracobrachialis muscle. Surg Radiol Anat 43(10):1581–1586
Olewnik Ł, Paulsen F, Tubbs RS et al (2021) Potential compression of the musculocutaneous, median, and ulnar nerves by a very rare variant of the coracobrachialis longus muscle. Folia Morphol 80(3):707–713
Olewnik L, Zielinska N, Karauda P, Duparc F, Georgiev GP, Polguj M (2021) 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. Surg Radiol Anat 43(5):661–669
Szewczyk B, Polguj M, Paulsen F et al (2021) A proposal for a new classification of coracobrachialis muscle morphology. Surg Radiol Anat 43(5):679–688
Wood J (1867) On human muscular variations and their relation to comparative anatomy. J Anat Physiol 1(1):44–59
Zielinska N, Olewnik L (2022) Six-headed coracobrachialis muscle. Folia Morphol 81(3):809–813
Acknowledgements
The authors would like to express their gratitude to body donors and their families for their highest contribution to medical education and anatomy research.
Funding
Open access funding provided by HEAL-Link Greece.
Author information
Authors and Affiliations
Contributions
Conceptualization: MP; cadaver’s dissection: MP, and GT methodology: DF, MP, GT, VK; data collection: GK, GT, EK; analysis and interpretation of results: MP, GT, CK; writing—original draft: DF, MP, GT; writing—review and editing: TT, KN, MS; critical revision of the manuscript: CK, DC; approval of the final version of the manuscript: all authors.
Corresponding author
Ethics declarations
Competing interests
The authors declare no competing interests.
Conflict of interest
The authors declare that they have no conflict of interest.
Ethical approval
As this is a case report that is completely on a cadaver, no ethical clearance was required as cadaver is used for teaching and research purpose.
Consent for publication
All the authors gave consent for the publication of the report.
Additional information
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
About this article
Cite this article
Filippou, D., Piagkou, M., Natsis, K. et al. A rare bilateral variant of the coracobrachialis muscle with supernumerary heads and coexisted variant branching patterns of the brachial plexus and the axillary artery. Surg Radiol Anat 45, 277–282 (2023). https://doi.org/10.1007/s00276-023-03088-w
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00276-023-03088-w