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ANATOMIC VARIATIONS

Anatomical variation in formation of brachial plexusand its branching

Anjali Aggarwal • Nidhi Puri • Aditya K. Aggarwal •

K. Harjeet • Daisy Sahni

Received: 7 March 2010 / Accepted: 17 May 2010 / Published online: 3 June 2010Ó Springer-Verlag 2010

Abstract Variant brachial plexus formation with twotrunks and two cords is uncommon and has clinicalimplications as it may result in failure of regional brachialor axillary block. During routine anatomical dissection,unilateral variation in the formation of brachial plexusaccompanied by unusual positional relationship with axil-lary artery was discovered in the left upper extremity of a52-year-old Indian male cadaver. Brachial plexus showedtwo trunks formed by ventral rami of C5, C6 and C7, C8,T1 spinal nerves, respectively, which rst split and thenreunited in an unusual manner to form two cords: posteriorand lateral instead of three. Medial cord was absent. Thebranching pattern of the brachial plexus also showedimportant variations. Second part of axillary artery wasfound lying inferomedial to brachial plexus instead of passing between medial and lateral cords. Transverse cer-vical artery was found to be coursing between two trunksinstead of passing supercial to brachial plexus. Mediannerve was observed to be formed from a single root, instead

of usual two roots. Embryologically, this rare variationmay be due to the development of axillary artery fromninth segmental artery instead of usual seventh cervicalintersegmental artery. Such rare variation is clinicallyimportant as this knowledge may help the anesthesiologistsand the surgeons to avoid any inadvertent damage to nervesand axillary artery during blocks and surgical interventions.

Keywords Brachial plexus ÁVariation ÁMedian nerve ÁAxillary artery

Introduction

Complex nature of the brachial plexus and its intimaterelationship with axillary artery has always been an area of interest not only for the anatomists but also for the clini-cians as well. Normally, ventral rami of C5 and C6 spinalnerves unite to form upper trunk, C8 and T1 ventral ramiunite to form lower trunk and C7 continues as middle trunk of brachial plexus. Anterior and posterior divisions of thetrunks unite in a systematic manner to form three cords, i.e.lateral, medial and posterior cords, named according totheir position relative to second part of axillary artery [ 13].Variations in the formation of trunk, cords and their sub-sequent branches have been well documented in literature[4, 9]. However, variation in the brachial plexus at alllevels right from the formation of trunks to the origin of terminal branches along with its aberrant relationship withaxillary artery stem is very rare.

Purpose of the present case report was to highlight therare variant formation of brachial plexus, its variant rela-tionship with axillary artery and its relevance in clinicalsituations especially during the surgical interventions.Embryological basis of this variation is also suggested.

Electronic supplementary material The online version of thisarticle (doi: 10.1007/s00276-010-0683-8 ) contains supplementarymaterial, which is available to authorized users.

A. Aggarwal ÁK. Harjeet ÁD. Sahni

Department of Anatomy, Post Graduate Institute of MedicalEducation and Research, Chandigarh 160012, India

A. K. AggarwalDepartment of Orthopaedic Surgery, Post Graduate Institute of Medical Education and Research, Chandigarh 160012, India

N. PuriDepartment of Anatomy, MMIMSR, Mullana, India

A. Aggarwal ( & )# 123-C Type V, Sector 24-A, Chandigarh 160023, Indiae-mail: [email protected]; [email protected]

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Surg Radiol Anat (2010) 32:891–894DOI 10.1007/s00276-010-0683-8

http://dx.doi.org/10.1007/s00276-010-0683-8

http://dx.doi.org/10.1007/s00276-010-0683-8



Case report

The brachial plexus with variations in its formation and itsrelationship with the axillary artery was found in the leftupper extremity of a 52-year-old embalmed male cadaverduring routine dissection for undergraduate teaching(Figs. 1, 2). In right upper extremity, brachial plexus and

axillary artery showed normal anatomy.Ventral rami of C5 and C6 spinal nerves united to

constitute upper trunk (UT), which bifurcated unequallyinto a thicker posterior (PD) and a thinner anterior divi-sions (AD). Posterior division gave off the suprascapularnerve. Ventral rami of C7, C8 and T1 spinal nerves uniedinto a single common at lower trunk (LT) which wasalmost double the thickness of upper trunk. Lower trunk was divided into two sub-trunks; for the purpose of description we named them as LT1 and LT2, respectively.Both sub-trunks namely, LT1 and LT2 divided into ananterior and a posterior division (AD and PD). Anteriordivision of upper trunk while descending anterior to pos-terior division of LT2 was joined on its deeper aspect byanterior division of LT2 and subsequently by anteriordivision of LT1 to constitute a unied cord named as lateralcord (LC). Posterior divisions of upper trunk, LT1 and LT2merged together to form the posterior cord (PC). Posteriorcord was placed in a posterolateral plane relative to thelateral cord.

Medial and lateral pectoral nerves emanated fromanterior aspect of the lateral cord. After giving rise to themedial cutaneous nerve of arm from its medial aspect,lateral cord divided into four terminal branches namely:musculocutaneous nerve from the lateral aspect, ulnarnerve and medial cutaneous nerve of forearm from themedial aspect and median nerve lying in intermediate

position. Median nerve was formed from a single rootoriginating from the lateral cord. Posterior cord terminatedinto radial and axillary nerves. Thoracodorsal nerve ema-nated from the radial nerve. Lower subscapular nerve arosefrom the thoracodorsal nerve, whereas axillary nerve gaveoff upper subscapular nerve.

Second part of axillary artery was found lying infero-medial to the cords of brachial plexus and further distally itwas seen coursing laterally after passing deep to the ter-minal branches of lateral cord. In posterior triangle,transverse cervical artery after arising from the subclavianartery passed laterally lying supercial to the unied lowertrunk. Further, it plunged into the gap between two trunksand then coursed laterally lying deep to the upper trunk.Suprascapular artery traversed laterally supercial to LT1and LT2 and deep to anterior division of the upper trunk and further laterally supercial to posterior division of upper trunk. Branches of axillary artery did not demon-strate any variation from the standard described anatomy.Axillary vein was placed medial to axillary artery.

Discussion

In this case report, variation in the formation of brachialplexus was observed right from the level of trunk. It wasmarked by the formation of two trunks instead of three. Wereport a union of ventral roots of C7, C8 and T1 spinalnerves to form lower trunk with absent middle trunk. Suchuncommon variation has also been reported by Matejeik [5] (3 cases) and Yang [ 14] (1 case). Fusion of bers of C7spinal nerves into upper trunk has more commonly beenreported than that into lower trunk [ 8, 10, 12]. Uysal [ 12]reported absent lower trunk in 9% and absent upper trunk in 1% cases. In our case the lower trunk was formed byfusion of middle and lower trunks. Subdivision of lowertrunk into two sub-trunks and their further bifurcation intoanterior and posterior divisions was another unusual featureof the present study which has not been reported in liter-ature so far. In this case report, three anterior divisionsmerged into a single cord instead of forming lateral andmedial cords. Only a few studies have reported fusion of lateral and medial cords in the literature [ 4, 9, 13]. Kerr [ 4]found three cases in which lateral and medial cords fusedinto a single cord placed anterior to the axillary artery.Fused cord and posterior cord were found anterior andposterior to the artery, respectively, whereas in our casefused and posterior cords were found lateral and postero-lateral to the artery, respectively. Yang et al. [ 14] reportedformation of brachial plexus from two trunks and two cordsin one case but subdivision of fused lower trunk was notobserved. In the study by Pandey et al. [ 9], medial andlateral cords were united by a communicating branch rather

Fig. 1 Dissection of the left side of neck and axilla. Axn axillarynerve, Ax.art axillary artery, LC lateral cord, LT lower trunk, LT1lower subtrunk1, LT2 lower subtrunk2, Lsn lower subscapular nerve, Mcn musculocutaneous nerve, Mcna medial cutaneous nerve of arm, Mcnf medial cutaneous nerve of forearm, Mn median nerve, PC posterior cord, Rn radial nerve, Sn suprascapular nerve, S.art suprascapular artery, Tdn thoracodorsal nerve, Tr.cer.art transversecervical artery, Un ulnar nerve, Usn upper subscapular nerve, UT upper trunk

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than proper fusion as seen in the present study. Complete

fusion as seen in our case was reported by Yang et al. [ 14].The three cords of brachial plexus have received theirnames according to their relationship with the second partof axillary artery [ 3, 13]. Only two cords were noticed inthis case report namely, posterior and lateral cords. Medialcord was absent.

Suprascapular nerve in our case was found to be arisingfrom posterior division of upper trunk. A few studies havealso reported variant origin of suprascapular nerve fromposterior division of upper trunk instead of upper trunk [ 1,2].

In this case report, lateral cord was found to be termi-

nating into musculocutaneous, median and ulnar nervesrepresenting terminal branches of lateral and medial cords.Normally axillary artery is clasped on its medial and lateralaspects by medial and lateral roots of the median nerve,respectively. In present study, the axillary arterial stemfailed to pass through the brachial plexus. Thus, the char-acteristic loop of median nerve which is formed by bran-ches from lateral and medial cords was not seen as it arosefrom the single cord. Instead, it was formed from a singleroot which might be attributed to union of two cords. Suchfeature of single root median nerve has also been reportedin the literature [ 14]. In this case report, posterior cord gaverise to two terminal branches namely, radial and axillarynerves. Thoracodorsal nerve arose from radial nerve. Uppersubscapular nerve originated from the axillary nerve,whereas lower subscapular nerve arose from thoracodorsalnerve. A few studies have reported the origin of upper andlower subscapular nerves from axillary nerve [ 2, 4, 11 ].Kerr [ 4] has described the origin of thoracodorsal nervefrom the radial nerve.

Miller [ 6] and Mu ller [7] explained relationship betweenaxillary artery and brachial plexus as a combination of

embryological and evolutionary process. Mu ¨ ller [7]

hypothesized that axillary artery was formed by anasto-mosis of local vessels and alteration in the level of pene-tration of brachial plexus by the artery might depend uponits embryological origin from the intersegmental artery.Usually axillary artery is considered to be the continuationof seventh intersegmental branch of dorsal aorta whichpenetrates the plexus between middle and lower trunks.Sometimes the axillary artery is derived from 6th, 8th or9th intersegmental branch of dorsal aorta, thus resulting inthe altered relationship of axillary artery and brachialplexus [ 3, 6]. In this case report, arterial stem lays caudal tothe brachial plexus. Such caudal positioning of arterial

stem in relation to brachial plexus has been reported in afew studies [ 6, 14]. Probable source of origin of axillaryartery in the present study was from 9th segmental arteryand a part of the seventh persisted as a branch of it andgave rise to transverse cervical artery which thus traversedthrough the gap between two trunks. This assumption isbased on the hypothesis described by Miller [ 6]. In hisstudy, main stem of the axillary artery was arising from 9thsegmental artery in one case. Remnant of seventh seg-mental artery branched off from it which passed throughthe median loop and developed into deep brachial andhumeral circumex arteries. Generally, the transverse cer-vical artery, a branch of subclavian artery passes laterallysupercial to the brachial plexus. In our case, it was foundcoursing between upper and lower trunks. Until now thereis no experimentally proved explanation of exact origin of arterial stem. This variant passage of transverse cervicalartery between upper and lower trunk has not been reportedin the literature so far.

Thus, the knowledge of relationship of the brachialplexus with the axillary artery is paramount to ensure safeand successful regional anesthesia of upper extremity.

Fig. 2 Schematic diagram of left brachial plexus. Forabbreviations see Fig. 1

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Variant formation of brachial plexus with supercialposition of axillary artery may lead to injury during surgeryin upper axilla. Hence, such variations are of clinicalimportance to the anesthesiologists and the surgeons.Supra- or infraclavicular brachial plexus block may inad-vertently damage the artery.

Acknowledgments The authors wish to thank Mr. Vijay Bakshisenior artist of Department of Anatomy for drawing the illustration.

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