Anatomy of the Brachial Plexus : A Rare Variation in the Laboratory of Anatomy of Bamako ( Mali )

The brachial plexus (BP), established by the lap twigs of the last four cervical nerves and the first thoracic nerve, assures the driving and sensory innervation of the thoracic member. We bring back a case of rare anatomical variation of the brachial plexus. It is a 34-year-old corpse dissected in the laboratory of anatomy of the Faculty of Medicine and Odontostomatology of Bamako in September 2017. The lap twig of the fourth cervical root (C4) participated in the constitution of the brachial plexus. The superior trunk was normally constituted. The average trunk was formed by the cervical roots C7 and C8 instead of only C7. And consequently the inferior trunk was constituted by the thoracic root T1. The posterior beam was only formed by the posterior branches of the superior and more average trunk. The medial beam was formed by all of the inferior trunk which did not give posterior branch for the formation of the posterior beam. The variations of the brachial plexus could entrain failures in the loco regional anesthesia of the brachial plexus.


Introduction
The brachial plexus (BP), constituted by the lap twigs of the last four cervical nerves and the first thoracic nerve, assures the driving and sensory innervation  [1]. The hurts of the brachial plexus are frequent [2] [3].
It is about strains or break by obstetric drive or by trauma of the cervical rachis, the slipped discs and the cervical degenerative osteoarthritis. The magnetic resonance imaging (MRI) is the examination of reference imaging for the exploration of the brachial plexus [4].
The microsurgery considerably improved the results of the surgery of the hurts of the brachial plexus [3].
We report a case of rare anatomical variation of the brachial plexus.

Case Report
It is about a 34-year-old corpse dissected in the laboratory of anatomy of the Muscles scalene were ruled out to dissect and highlight roots. In the region axillary the pectoral big and small muscles which established the plan of lap cover of the BP, were cut to dissect well the beams and the terminal branches.
The artery axillary and the coraco-brachial muscle were marks important for the identification of the musculo-cutaneous and median nerves. The radial nerve and the nerve axillary were looked for behind the artery axillar.

At the Level of the Root of the Brachial Plexus
The lap twig of the fourth cervical root (C4) participated in the constitution of the brachial plexus ( Figure 1). Forensic Medicine and Anatomy Research

Constitution of the Trunks of the Brachial Plexus
The superior trunk was normally constituted. The average trunk was formed by the cervical roots C7 and C8 instead of only C7. And consequently the inferior trunk was constituted by the thoracic root T1 (Figure 1).

Training of the Beams of the Brachial Plexus
The later beam was only formed by the later branches of the superior and more average trunk. The beam medial was formed by all of the inferior trunk which did not give posterior branch for the training of the posterior beam ( Figure 2).

Terminal Branches of the Brachial Plexus
We found that: The low birth of the musculo-cutaneous nerve, The high birth of the cutaneous medial nerve of the arm. The nerve ulnar, the branch medial of the median nerve, the cutaneous medial nerve of the arm and the cutaneous medial nerve of the front arm arose from the inferior trunk ( Figure 2).
We did not note participation of T2 in the constitution of the brachial plexus.

Participation of the Cervical Root C4 in the Constitution of the Brachial Plexus
There are numerous variations of constitution of the brachial plexus. The most frequent are the brachial said plexus "prefixed" with the cooperation of the previous branch of C4. In our observation, the lap twig of the fourth cervical root (C4) participated in the constitution of the brachial plexus. It was 41% in the series of B. Senecail [5], 30.4% in the series of Ongoïba on 23 dissections. Kerr [6] found 65.9% and 60% in two series of 56 and 54 cases while Lee [7] found only 22.4% of participation of C4 in the BP on 152 dissections. Forensic Medicine and Anatomy Research The "postfixed" said brachial plexus with the cooperation of the previous branch of T2 is rarer, met in 5% of the cases [5]. In our observation, we did not find this participation.

Variation Fascicular of the Brachial Plexus
At the level fascicular, we found in our observation the following variations: The posterior beam was only formed by the posterior branches of the superior and more average trunk.
The side beam was normally constituted.
The medial beam was formed by all of the inferior trunk which did not give posterior branch for the formation of the posterior beam.
Ongoïba found two cases of variation fascicular of the brachial plexus on 23 cases of dissection. In the first variation he describes an abnormal fusion of three beams from where were born all the terminal branches. In its second variation, the pectoral small nerve had one is born low in the region of the beams.

Terminal Branches
The variations found at the level of the terminal branches concerned the low birth of the musculo-cutaneous nerve, the high birth of the cutaneous nerve medial of the arm. The branch medial of the median nerve, the cutaneous nerve medial of the arm and the cutaneous nerve medial of the front arms arose from the inferior trunk because this one formed the beam medial. Ongoïba [3] found in 34.8% (8 cases on 23 dissections) of variations of the terminal branches and among these 13% concerned the unusual seat of the musculo-cutaneous nerve.

Conclusion
The variations of the brachial plexus could entrain failures in the loco regional anesthesia of the brachial plexus. The surgery of the lesional pathologies of the brachial plexus requires the perfect knowledge of its anatomical variations.

Authorization of the Ethics Committee
We, undersigned, authors of this article, give evidence to have received the