A bilateral four-headed brachialis muscle with a variant innervation: a cadaveric report with possible clinical implications.

PURPOSE: Anterior compartment muscles of the arm present high morphological variability, with possible clinical significance. The current cadaveric report aims to describe a bilateral four-headed brachialis muscle (BM) with aberrant innervation. Emphasis on the embryological background and possible clinical significance are also provided. METHODS: Classical upper limb dissection was performed on an 84-year-old donated male cadaver. The cadaver was donated to the Anatomy Department of the National and Kapodistrian University of Athens. RESULTS: On the left upper limb, the four-headed BM was supplied by the musculocutaneous and the median nerves after their interconnection. On the right upper limb, the four-headed BM received its innervation from the median nerve due to the musculocutaneous nerve absence. A bilateral muscular tunnel for the radial nerve passage was identified, between the BM accessory heads and the brachioradialis muscle. CONCLUSION: BM has clinical significance, due to its proximity to important neurovascular structures and frequent surgeries at the humerus. Hence, knowledge of these variants should keep orthopedic surgeons alert when intervening in this area. Further dissection studies with a standardized protocol are needed to elucidate the prevalence of BM aberrations and concomitant variants.

The coracobrachialis muscle: typical morphology, accessory forms, and the issues with terminology.

The coracobrachialis muscle (CB) represents one of the anterior arm compartment muscles. It has been defined by classic anatomy textbooks and old papers, as a muscle of one belly arising from the coracoid process tip and partially from the tendon of the biceps brachii short head, and inserted into the humeral shaft, above the bone's midpoint. However, recent cadaveric studies have confirmed that in the majority of cases, the CB is a two-headed muscle consisting of a superficial and a deep head. This finding has caused confusion regarding the terminology of CB's morphology. Typical CB morphology, according to recent data should not be considered the muscle of one belly, but the two-headed muscle. In particular, the musculocutaneous nerve's (MCN) course plays an important role in defining the CB morphological characteristics. If the MCN courses medially to the CB, with no signs of penetration after dissection, it can be concluded, that the CB is composed of one head; otherwise, if the muscle is composed of two or more heads, the MCN will courses between the CB bellies. In conclusion, it is of paramount importance to adopt common-universal terminology. Hence, considering recent findings, if the CB origin and/or the insertion differs from the typical anatomy, an "atypical CB" is the proper definition of the muscle, while if this "atypical CB" coexists with a typical CB, the terminology "accessory CB" may be used.

A Review of the Typical Course of the Musculocutaneous Nerve into the Coracobrachialis Muscle: Its Variability and Possible Clinical Implications.

OBJECTIVE: This literature review highlights the prevalence of the typical course of the musculocutaneous nerve (MCN) through the coracobrachialis muscle (CB), and evaluates the distance from the entrance point of the MCN to the CB, taking the coracoid process (CP) as a landmark. METHODS: PubMed (MEDLINE), Scopus, and CINAHL online databases were searched in December 2022 for studies reporting the prevalence of the MCN's typical course and the distance between the CP and the MCN entrance point to the CB. RESULTS: Twenty-eight studies were included (including 2846 subjects) investigating the MCN's typical course, and eliciting a prevalence of 93.4%. The mean distance of the CP to the entrance point of the MCN's main trunk into the CB was 5.6±2cm (median 6.1cm, in 550 subjects). In 76.12% of cases the MCN's accessory branches entered the CB proximally to the MCN's main trunk. The mean distance from the CP to the entrance point of the MCN's proximal branches to the CB was 3.8±1.2cm (median 3.7cm, in 140 subjects). CONLCUSION: In the vast majority of cases, the MCN had a typical course through the CB. In cases of altered anatomy, the MCN was either absent or passed medially to the CB (without piercing it). The average entrance point of the MCN into the CB from the CP is 5.6 cm. Proximal motor branches of the MCN to the CB are common and usually arise at a mean distance of 3.8cm from the inferior border of the tip of the CP. Surgeons should be aware of both the MCN's typical and its atypical course and these distances to avoid possible complications when operating in the area.

Muscle interconnections in the anterior and posterior arm compartment: a cadaveric case series with possible clinical implications.

PURPOSE: The report describes four cases of accessory bundles (ABs) or fibers connecting the muscles of the anterior with the posterior arm compartment. The ABs morphology (pure muscular or musculofascial or musculoaponeurotic) is described emphasizing their attachment points, characterized as muscles' interconnections. MATERIALS AND METHODS: Four formalin-embalmed donated male cadavers were dissected. RESULTS: The muscles' interconnections were unilaterally identified. In the first case, the two ABs originated from the coracobrachialis muscle (CB), received fibers from the biceps brachii (BB), and were inserted into the triceps brachii (TB) medial head. The ABs created an arch over the brachial vessels and the median nerve (MN). In the second case, an accessory musculoaponeurotic structure was identified between CB and TB medial head and extended over the brachial vessels. In the third case, the myofascial ABs between the BB short head and the upper arm fascia, coursed anterior to the MN, the brachial artery, and the ulnar nerve, with direction to the TB medial head. In the fourth case, the three muscular ABs originating from the CB superficial and deep heads, in common with the BB short head, joined the upper arm fascia and the TB medial head and possibly entrapped the musculocutaneous nerve, the MN, and the brachial artery. CONCLUSION: ABs or musculoaponeurotic extensions may predispose to complications due to their potential compression on nerves and vessels. Clinicians should consider the possible existence of such bridging variants between muscles, in the differential diagnosis of a patient presenting with ischemia, edema, or MN palsy symptoms.

Coracobrachialis muscle morphology and coexisted neural variants: a cadaveric case series.

PURPOSE: The current cadaveric case series evaluates the coracobrachialis muscle morphology, the related musculocutaneous nerve origin, course, and branching pattern, as well as associated adjacent neuromuscular variants. MATERIALS AND METHODS: Twenty-seven (24 paired and 3 unpaired) cadaveric arms were dissected to identify the coracobrachialis possible variants with emphasis on the musculocutaneous nerve course and coexisted neural variants. RESULTS: Four morphological types of the coracobrachialis were identified: a two-headed muscle in 62.96% (17/27 arms), a three-headed in 22.2% (6/27), a one-headed in 11.1% (3/27), and a four-headed in 3.7% (1 arm). A coracobrachialis variant morphology was identified in 37.04% (10/27). A three-headed biceps brachii muscle coexisted in 23.53% (4/17). Two different courses of the musculocutaneous nerve were recorded: 1. a course between coracobrachialis superficial and deep heads (in cases of two or more heads) (100%, 24/24), and 2. a medial course in case of one-headed coracobrachialis (100%, 3/3). Three neural interconnections were found: 1. the lateral cord of the brachial plexus with the medial root of the median nerve in 18.52%, 2. the musculocutaneous with the median nerve in 7.41% and 3. the radial with the ulnar nerve in 3.71%. Duplication of the lateral root of the median nerve was identified in 11.1%. CONCLUSIONS: The knowledge of the morphology of the muscles of the anterior arm compartment, especially the coracobrachialis variant morphology and the related musculocutaneous nerve variable course, is of paramount importance for surgeons. Careful dissection and knowledge of relatively common variants play a significant role in reducing iatrogenic injury.

A rare bilateral variant of the coracobrachialis muscle with supernumerary heads and coexisted variant branching patterns of the brachial plexus and the axillary artery.

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.

Proportional localisation of the entry point of the coracobrachialis muscle by the musculocutaneous nerve along the humerus.

PURPOSE: To project the distance between the tip of the greater tubercle (GT), respectively, the proximal border of the tip of the coracoid process (CP) and the entry point of the coracobrachialis by the musculocutaneous nerve (MCN) proportionally onto the humeral length. METHODS: Sixty-six upper extremities were included in the study. The distance between the tip of the GT and the distal tip of the lateral humeral epicondyle (LE) was evaluated as the humeral length (HL). The interval between the tip of the GT and the entry point of the coracobrachialis muscle by the MCN was measured. The distance between the proximal border of the tip of the CP and the distal portion of the medial humeral epicondyle (ME) and the entry point of the MCN into the coracobrachialis were evaluated. Proportions were used to project the entry point of the coracobrachialis by the MCN along the HL, respectively, the interval between the proximal border of the tip of the CP and the distal tip of the ME. RESULTS: The entry point of the MCN into the coracobrachialis muscle can be expected at an interval between 14.9 and 33.9% of the HL (between the tip of the GT and the LE), starting from the tip of the GT. Regarding the reference line between the proximal border of the CP and the ME, the nerve's entry point was located between 14.2 and 34.4%, starting from the CP. CONCLUSION: Results represent easily applicable intervals for intraoperative localisation of the MCN.

A new type of the coracobrachialis muscle.

The coracobrachialis muscle belongs to the anterior group of the brachial region. Its main functions are flexion and adduction at the glenohumeral joint. It is highly morphologically variable, especially in the number of bellies, place of origin or insertion, and its relationship to the musculocutaneous nerve. Accessory structures associated with the coracobrachialis muscle include the coracobrachialis brevis or coracobrachialis longus muscle. The present case describes a three-headed coracobrachialis muscle with two such additional structures. One of these has a tendinous origin connected to the periosteum and located on the surgical neck of the humerus. Its insertion is fused with the third head of the coracobrachialis muscle. The other has a proximal attachment fused with the capsule of the shoulder joint, and its distal attachment is fused with the third head of the coracobrachialis muscle in place of its connection with the short head of the biceps brachii. This could result in better stabilisation of the glenohumeral joint; on the other hand, it could limit operational access during treatment of subscapularis tears.

The pattern of branching and intercommunications of the musculocutaneous nerve for surgical issues: anatomical study.

BACKGROUND: The aim of the present work was to provide evidence about the anatomical variations as regard the origin, distribution, and branching pattern of the musculocutaneous nerve (MCN). MATERIALS AND METHODS: Brachial plexus was dissected in 40 upper limbs of 20 male adult cadavers. The pattern of the MCN was photographed by a digital camera. RESULTS: The location and length of the nerve branches between left and right arms were recorded and statistically analysed. In 90% of specimens the MCN originates from the lateral cord of the brachial plexus, in 5% it arose from the median nerve (MN), while in the remaining 5% specimen, it was absent. The MCN pierced the coracobrachialis muscle in 90% of specimens, and in the remaining 10% did not pierce it. The motor branches to biceps brachii muscle were categorised into: type 1 (90%): one branch that divides to supply the two heads of biceps; type 2 (5%): double branches, innervating each head of biceps separately. The motor branches to brachialis muscle were categorised into: type 1 (82.9%): one branch; type 2 (14.2%): double branches and type 3 (2.9%): three branches that innervating brachialis muscle. Communications between the MCN and the MN were observed in 35% of specimens. CONCLUSIONS: The knowledge of the common and uncommon MCN variations is important especially to the surgeons for carrying out surgical procedures in axilla and arm.

Six asymmetric bilateral additional heads of biceps brachii muscle observed in a cadaver / Seis cabezas adicionales bilaterales asimétricas del músculo bíceps braquial observadas en un cadáver

SUMMARY: Anatomic variation of the biceps brachii muscle (BBM) is frequently observed; its pattern is diverse and clinically important. During the educational dissection of a 78-year-old Korean male cadaver, six additional asymmetrical heads of the biceps brachii muscle (BBM) were found on both sides. On the right side, two additional heads originated from the humerus; the musculocutaneous nerve passed between these heads and the short head of the BBM. Four additional heads were found on the left side, anterior to the BBM, one of which originated from the pectoralis major muscle. Posterior to the BBM, two heads of tendons originated from the coracobrachialis muscle and one head of the muscle belly originated from the humerus. The left musculocutaneous nerve pierced the coracobrachialis muscle and continued distally passing between the short head of the BBM and the additional heads located posterior to the BBM. It then gave off the variant musculocutaneous nerve to the median nerve. On both sides, the short and long heads of the BBM had normal origins, insertions, and courses. This novel variation has various clinical and embryological implications.

RESUMEN: Con frecuencia se observa una variación anatómica del músculo bíceps braquial (MBB); su patrón es diverso y clínicamente importante. Durante la disección de un cadáver masculino coreano de 78 años, se encontraron seis cabezas asimétricas adicionales del músculo bíceps braquial en ambos lados. En el lado derecho, dos cabezas adicionales se originaban en el húmero; el nervio musculocutáneo atravesaba entre estas cabezas y la cabeza corta del MBB. Se encontraron cuatro cabezas adicionales en el lado izquierdo, anterior al MBB, una de las cuales se originaba en el músculo pectoral mayor. Posterior al MBB, dos cabezas tendinosas se originaban en el músculo coracobraquial y una cabeza de vientre muscular se originaba en el húmero. El nervio musculocutáneo izquierdo perforaba el músculo coracobraquial y continuaba distalmente pasando entre la cabeza corta del MBB y las cabezas adicionales ubicadas por detrás del MBB. Luego emitía la variante el nervio musculocutáneo al nervio mediano. En ambos lados, las cabezas corta y larga del MBB tenían orígenes, inserciones y trayectos normales. Esta nueva variación tiene varias implicaciones clínicas y embriológicas.

Aberrant arrangement of the musculocutaneous and median nerves in the thoracic limbs of a mixed-breed dog cadaver.

In the left thoracic limb of a male cadaver (adult mixed-breed dog), the median nerve (MN) after departing from the common median/ulnar nerve (UN) trunk received two branches. One from the lateral thoracic nerve (LTN) and the other from the musculocutaneous nerve (MCN). These both passed cranial to the axillary artery at the level of the lateral thoracic artery and joined the median nerve. Thus, in the proximal brachium, the axillary artery was cradled by this union, similar to the ansa axillaris of large animals and similar formations reported in human and non-human primates. In the distal brachium, the communicating branch ran unusually from the MN to the MCN on the left, and in both directions on the right. Awareness of such anatomical variations of the terminal branches of the brachial plexus (BP) in addition to the embryonic and evolutionary aspects can be useful in explaining neuroarterial signs with unknown origin, as those reported in human medicine.

Six-headed coracobrachialis muscle.

The coracobrachialis muscle is the smallest muscle of the anterior compartment of the arm. It is responsible for flexion and abduction in the glenohumeral joint. The coracobrachialis muscle is morphologically variable both in its insertion and origin. Moreover, some additional heads or structures may also occur. The present report describes a six-headed coracobrachialis muscle originated as a common junctionwith the short head of the biceps brachii muscle from the coracoid process. All of these heads insert into the medial surface of the humeral shaft. It is important to note that the musculocutaneous nerve was piercing the fourth belly. Other heads were innervated by branches from the musculocutaneous nerve. Knowledge of the morphological variability of this muscle is essential not only for anatomists but for clinicians as well.

Two cases of variations of musculocutaneous nerve communication with the median nerve / Dos casos de variaciones de la comunicación del nervio musculocutáneo con el nervio mediano

SUMMARY: To know the nerve variations of brachial plexus and its branches is very important in the management of upper limb nerve injuries. Variations of the brachial plexus are not uncommon, but types of variations are diverse. The unusual communication branches between the musculocutaneous nerve (MCN) and the median nerve (MN) in course were found during routine dissection on the two different left arms of formalin fixed male cadavers. Depending on the position related to the coracobrachial muscle (CBM), one MCN pierced the CBM, the other did not in the two cases. The branches of MCN emerged interior to the coracoid process to innervate the CBM. The present case reports of anatomical variations of nerves can help to manage nerve injuries and plan surgical approaches during surgical procedures.

RESUMEN: Conocer las variaciones nerviosas del plexo braquial y sus ramas es muy importante en el tratamiento de las lesiones nerviosas de los miembros superiores. Las variaciones del plexo braquial no son infrecuentes, sin embargo los tipos de variaciones son diversos. Los ramos inusuales de comunicación entre el nervio musculocutáneo (NMC) y el nervio mediano (NM) en curso fueron descubiertos durante la disección de rutina en dos miembros superiores izquierdos de dos cadáveres de sexo masculino fijados con formalina. Un NMC atravesó el MCB, otro no lo hizo en los dos casos. Los ramos de NMC emergieron a nivel del proceso coracoideo para inervar el MCB. Los presentes informes de casos de variaciones anatómicas de los nervios pueden ayudar a tratar las lesiones nerviosas y planificar los abordajes quirúrgicos durante los procedimientos quirúrgicos.

Classification of the musculocutaneous nerve fetuses / Clasificación del nervio musculocutáneo en fetos

SUMMARY: The musculocutaneous nerve is a terminating branch of lateral cord of the brachial plexus and is formed from spinal roots of C5, C6 and C7. The anatomical variations of the musculocutaneous nerve (MCN) are not common, literary reports have described the different course of the MCN in the arm, however very few fetal studies have been conducted on the variations of the MCN. Therefore, the aim of this study was to describe the course of the MCN in fetuses and document variations, if any. In this study, a sample size of twenty-five fetuses were bilaterally dissected (n=50) using a stereomicroscope. The anatomy of the MCN was described using a classification system generated based on the findings of this study. Ethical clearance was obtained from Biomedical Research Ethics Committte (BE385/17). Type I (normal anatomy) of the MCN was found in 42/50 (84 %) of specimens in this study. This study found a few variations, viz. 1/50 (2 %) case of Type II (absent), 1/50 (2 %) Type III (communication between the MCN and MN, from the MN to the MCN), 4/50 (8 %) cases of Type IV (communication from the MCN to the MN) and 2/50 (4 %) cases of Type V (communication from the MCN to the MN, where the MCN does not pierce the coracobrachialis muscle). Therefore, this study provides evidence of variations of the MCN in fetuses that may help surgeons in the interpretation of abnormal innervation patterns in the arm.

RESUMEN: El nervio musculocutáneo es un ram terminal del fascículo lateral del plexo braquial y está formado por las raíces espinales de C5, C6 y C7. Las variaciones anatómicas del nervio musculocutáneo (NMC) no son comunes, los informes literarios han descrito el curso diferente del NMC en el brazo, sin embargo, se han realizado muy pocos estudios fetales sobre las variaciones de este nervio. Por lo tanto, el objetivo del estudio fue describir el curso del NMC en fetos y documentar las variaciones. En este estudio, una muestra de veinticinco fetos fue disecada bilateralmente (n = 50) usando un estereomicroscopio. La anatomía del NMC se describió mediante un sistema de clasificación en base a los hallazgos. La aprobación ética se obtuvo del Comité de Ética en Investigación Biomédica (BE385 / 17). El tipo I (anatomía normal) del NMC se encontró en 42/50 (84 %) de las muestras. Se observaron algunas variaciones, por ejemplo: 1/50 (2 %) caso de Tipo II (ausente), 1/50 (2 %) de Tipo III (comunicación entre NMC y nervio mediano (NM), de NM a NMC), 4/50 (8 %) casos de Tipo IV (comunicación del NMC al NM) y 2/50 (4 %) casos de Tipo V (comunicación del NMC al NM, donde el NMC no perfora el músculo coracobraquial). Este estudio proporciona evidencia de variaciones del NMC en fetos que puede ayudar a los cirujanos a interpretar patrones de inervación anormales en el brazo.

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

The coracobrachialis longus muscle (CBL) is an extremely rare variant of the coracobrachialis muscle (CRM). The CBL originates from the apex of the coracoid process together with the short head of the biceps brachii and inserts on the olecranon of the ulna. The CBL consists of three parts: a superior part (classical CRM - length 137.88 mm), a middle fibrous layer (23.41 mm), and an inferior part (185.37 mm). A rare relationship between the CBL and median, musculocutaneous and ulnar nerves was observed with potential compression at these three parts. In addition, this case report describes a connection between CBL and the medial head of the triceps brachii, as well as a third head of the biceps brachii, which originate from the fibrous layer. This case report highlights the relationships between the CBL and the median, ulnar and musculocutaneous nerves.

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.

The coracobrachialis muscle (CBM) originates from the apex of the coracoid process, in common with the short head of the biceps brachii muscle, and from the intermuscular septum. Both the proximal and distal attachment of the CBM, as well as its relationship with the musculocutaneus nerve demonstrate morphological variability, some of which can lead to many diseases. The present case study presents a new description of a complex origin type (four-headed CBM), as well as the fusion of both the short biceps brachii head, brachialis muscle and medial head of the triceps brachii. In addition, the first and second heads formed a tunnel for the musculocutaneus and median nerves. This case report has clear clinical value due to the split mature of the coracoid process, and is a significant indicator of the development of interest in this overlooked muscle.

Unusual formation of the musculocutaneous and median nerves: a case report refined by intraneural dissection and literature review.

This report presents a detailed anatomical investigation of an upper limb specimen showing an atypical formation of the musculocutaneous nerve (MCN) and median nerve (MN). The study was refined by intraneural dissection, which supplements earlier descriptions of similar anatomical variations and allows for revision of the accepted classification. The case described in this report was an incidental finding during routine dissection of a fixed isolated upper limb. Intraneural dissection revealed partial fusion between the MCN and aberrant bundles of the MN. Those aberrant bundles joined the main steam of the MN at the level at which the MCN branched off as an independent nerve. The procedure allowed the aberrant fibres of the MN to be differentiated from the MCN. The presence of separate bundles in a territory corresponding to the MCN was confirmed, although those bundles and the aberrant MN bundles were covered by a common epineurium. The aberrant MN bundles running within the MCN did not contribute to innervation of the forearm muscles. They rejoined the main nerve trunk in the arm. A comprehensive understanding of the diverse anatomical variations of the upper limb nerves could be crucial for the safety and success of surgical procedures, especially procedures for reconstructing the brachial plexus or its branches.

Anatomical Variation of a Communicating Branch between the Musculocutaneous and the Median Nerve: A Case Report.

OBJECTIVE: The aim of our paper is to depict an anatomical variation of the brachial plexus, concerning a communicating branch between the median and the musculocutaneous nerve and its clinical significance. Anatomical variations of the brachial plexus and especially those of the musculocutaneous nerve are quite common. Awareness of these variations is of paramount importance in clinical practice, mainly in achieving best results in minimal invasive or surgical procedures. CASE REPORT: After dissection in upper extremities in a 89-year-old male cadaver, a communicating branch between the median and the musculocutaneous nerve was found. This communicating branch was formed before the musculocutaneous nerve perforated the coracobrachialis muscle. It also derived from the level of the ansa medianis and its course was of an approximately 2cm length. CONCLUSION: The clinical significance of our study is the entrapment of the musculocutaneous nerve that may cause clinical findings similar to those of the carpal tunnel syndrome.

Positional anomaly between the brachial plexus and the scalene muscles, concomitant with an anomalous path of the musculocutaneous nerve: case report and clinical implication / Anomalía posicional entre el plexo braquial y el músculo escaleno anterior, concomitante con un trayecto anómalo del nervio musculocutáneo: reporte de un caso e implicancia clínica

Anatomical variations of the scalene muscles are frequent, as are those of the brachial plexus and its terminal nerves. Nonetheless, these variations are reported separately in the literature. The aim of this work is to present a variation of scalene muscles, concomitant with an abnormal path of the musculocutaneous nerve. During a routine dissection of the cervical region, axilla and right anterior brachial region in an adult male cadaver, a supernumerary muscle fascicle was located in the anterior scalene muscle, altering the anatomical relations of C5 and C6 ventral branches of the brachial plexus. This variation was related to an anomalous path of the musculocutaneous nerve that did not cross the coracobrachialis muscle. It passed through the brachial canal along with the median nerve. It then sent off muscular branches to the anterior brachial region and likewise, communicating branches to the median nerve. The concomitant variations of the brachial plexus and scalene muscles they are not described frequently. Knowledge of these variations improves diagnosis, enhancing therapeutic and surgical approaches by reducing the possibility of iatrogenesis during cervical, axillary and brachial region interventions.

Las variaciones anatómicas de los músculos escalenos son frecuentes, así como también las del plexo braquial y sus nervios terminales. Sin embargo la literatura científica las presenta por separado. El propósito de este trabajo es presentar una variación de los músculos escalenos concomitante con un trayecto anómalo del nervio musculocutáneo. Disección de rutina de región cervical, axila y región braquial anterior derechas realizada en un cadáver adulto de sexo masculino. Se encontró un fascículo muscular supernumerario para el músculo escaleno anterior que alteraba las relaciones anatómicas de los ramos ventrales C5 y C6 del plexo braquial. Esta variación estaba acompañada por un trayecto anómalo del nervio musculocutáneo, el cual no atravesaba al músculo coracobraquial y transitaba por el conducto braquial acompañando al nervio mediano. Desde allí enviaba a la región braquial anterior ramos musculares y al nervio mediano ramos comunicantes. Las variaciones conjuntas del plexo braquial y los músculos escalenos no se presentan con frecuencia. Conocerlas enriquece la capacidad diagnóstica, terapéutica y quirúrgica. Reduciendo la posibilidad de iatrogenia al intervenir en las regiones cervical, axilar y braquial.