Introduction Variations in the brachial plexus are the rule rather than the exception. This fact is of special interest for the anesthetist when planning axillary block of brachial plexus. Material and methods 167 cadaver arms were evaluated for variations in brachial plexus, with focus on the cords of the plexus, the loop of the median nerve, and the course of the median, musculocutaneous, ulnar, axillary and radial nerves. In addition, concomitant arterial variations were recorded. Results In 167 arms, variations were detected in 60 cases (36%). With 46 arms (28%) most variations concern the median nerve, followed by 13 cases (8%) which involved the musculocutaneous nerve. Ulnar, axillary and radial nerve variations were rare, amounting to 1.2% for each nerve. In median nerve conditions with a shifted loop of median nerve (12%), a hidden position of the loop or a hidden course of the beginning median nerve (8%) and a doubled loop of median nerve (17%) were observed. In musculocutaneous nerve conditions with a non-perforated coracobrachialis (1.8%), a doubled origin of the nerve (1.2%) and a giving back of branches to the median nerve (1.8%) were noted. Variations in ulnar, axillary and radial nerves concerned lower than normal diameters. Conclusions It must be stressed that cases which showed a hidden position or a doubled expression of the loop of the median nerve, a hidden course of its beginning and variable interconnections between musculocutaneous and median nerves are of special interest for anesthetists and surgeons. Hence, it is important to note that variations of arm arteries can be associated with brachial plexus variations. For example, a common trunk of axillary artery followed by a hidden loop and course of the median nerve may result in incomplete axillary block of brachial plexus.

Variations in brachial plexus with respect to concomitant accompanying aberrant arm arteries

In classic anatomy teaching, the brachial plexus generally features as an enigmatic rote-learned structure, leaving the student with a feeling of complexity. The notion of complexity may increase in dissections, where plexuses significantly differing from the standard plexus model are readily found. This raises questions: what determines the existence and prevalence of variants and to what degree should they be considered anomalous? A model linking brachial plexus morphology and its variability to causative morphological parameters which would also standardize plexus description and teaching would be beneficial. The present study aims to provide such a model by analyzing the context of plexus development and applying this model in the analysis of plexus variability in anatomical specimens. Based on a thorough literature review, a generic developmental model was formulated and different factors of variability defined. In 56 plexuses, the proposed generic principles of plexus variability were found consistent with the variations encountered. Summarized, the modeled generic principles are as follows. Brachial plexus axon bundles grow out into an environment of chemical tracer paths in which constraints and obstacles are present: the geometry of the arm bud, cartilaginous bone precursors and vessels. The overall constancy of these factors generates a gross plexus outline, while the variability in these factors gives rise to typical plexus variations. The usefulness of the model derives from the fact that the variability of the main morphologically determining factors is not random but is the expression of the possibilities of the embryological substrate. Within the model, the major plexus morphological determinant is the segmental position of the subclavian artery, which is determined by the segment level of the intersegmental artery from which it develops. Normally, the subclavian artery develops from intersegmental artery i7. However, the subclavian artery can develop from inferior or superior segmental levels, from intersegmental artery i8 or i6, and possibly also from i9 or i5. Each of these arterial variants creates a typical, morphologically distinct, predictable plexus configuration. Superimposed on these basic plexus configurations, the underlying embryological substrate may develop further variability by integrating remnants of other intersegmental arteries into the arterial network. The resulting plexus configurations are further modified by local factors, e.g. the splitting of outgrowing axon bundles around vessels. A large split in the lateral cord around a large vein or veins crossing from lateral to medial, tangentially cranially over the subclavian artery was found in 54% of the 56 investigated BP and therefore might be added to plexus teaching. The distinct plexus morphologies associated with the subclavian artery segmental levels were further found associated with, among others, typical variations in the pectoral nerves and their ansas; these associations were also modeled. The presented models could allow brachial plexus rote learning to be replaced by a more insightful narrative of formative principles suitable for teaching. Clinically, improved understanding of the relationship between plexus variability and the local anatomical environment should be relevant to brachial plexus surgery and reconstruction.

The brachial plexus – explaining its morphology and variability by a generic developmental model

Address for Correspondence: Dr. Gabriel J Mchonde, Department of Cell Biology and Neuroanatomy, School of Medicine, Iwate Medical University, Iwate, Japan. Nishitokuda 2-1-1, Yahaba-cho, Shiwa-gun, 028-3694, Contact no.+81 80 6293 4529. E-Mail: gmchonde@yahoo.co.uk or mchonde@iwate-med.ac.jp Access this Article online Quick Response code Web site: 1* PhD Student, Department of Cell Biology and Neuroanatomy, School of Medicine, Iwate Medical University, Japan. 2 Professor of Anatomy, Department of Anatomy and Histology, School of Medicine, International Medical and Technology University. 3 Lecturer, Department of Anatomy and Histology, School of Medicine, International Medical and Technology University. Background: Variations in formation of brachial plexus roots, trunks, divisions and cords are not uncommon and maybe of important in regional anaesthesia involving the upper limb. However, in the present case we are reporting a rare bilateral multiple variations observed during routine dissection on a 77-years-old embalmed male cadaver on left and right brachial plexus. Understanding the anatomical variations involving brachial plexus is important and might benefit the physicians, surgeons, anaesthesiologists and neuroanatomists during their routine procedures involving the cervical, axillary and the upper limb regions.

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Bilateral multiple variations in the formation of the brachial plexus and its terminal nerves: a case report

The brachial plexus is a complicated plexus supplying the upper limb. The brachial plexus is of great practical importance to the surgeon. It is encountered during operations upon the root of the neck, and hence it is in danger. Variations in the formation of the brachial plexus are common; and knowledge of the variation of the brachial plexus may be useful for surgeons, for improved guidance during supraclavicular block procedures, and for surgical approaches for brachial plexus. Here we report a case in which the superior trunk of the brachial plexus was found to be absent on the right side during a study on the cadaver-neck specimens in the Department of Anatomy.

Absence of upper trunk of the brachial plexus.

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Absence of upper trunk of the brachial plexus.