During routine anatomical dissections, absence of the musculocutaneous nerve
was determined in a 58-year-old male cadaver. Moreover, the biceps brachii
and brachialis muscles were innervated by two separate branches which divided
from the median nerve instead of the musculocutaneous nerve. From a branch
that divides from the main trunk of the median nerve at nearly the middle of the
arm a motor branch again divided that innervated the brachialis muscle and
a sensory branch that conveyed the sense of the lateral part of the forearm.
Furthermore, it was found that the brachial artery divided into its terminal branches,
the radial and ulnar arteries. We believe that this rare variation of the median
nerve will shed light upon surgical procedures involving the median nerve

Aydin, M.E.

Demir, M.T.

Edizer, M.

Kale, A.

Kopuz, C.

Çorumlu, U.

English

Via Medica Journals

Folia Morphol. Vol. 65, No. 3, pp. 228–231Copyright © 2006 Via MedicaISSN 0015–5659www.fm.viamedica.plC A S E  R E P O R T228Address for correspondence: Assist. Prof. Dr. M.E. Aydin, Yeni Mahalle, Giresun Sok., Kardelen Sitesi, D-Blok, No. 7, Atakent-Samsun, Turkey,Fax: 0 90 362 4576091; e-mail: mepaydin@yahoo.com*Presented at the Sixth International Symposium of Clinical Anatomy, 8–10 October, Varna-BulgariaAbsence of the musculocutaneous nervetogether with unusual innervation of themedian nerve*M.E. Aydin, A. Kale, M. Edizer, C. Kopuz, M.T. Demir, U. ÇorumluOndokuz Mayis University, Medical Faculty, Department of Anatomy, Samsun, Turkey[Received 21 October 2005; Revised 5 June 2006; Accepted 5 July 2006]During routine anatomical dissections, absence of the musculocutaneous nervewas determined in a 58-year-old male cadaver. Moreover, the biceps brachiiand brachialis muscles were innervated by two separate branches which dividedfrom the median nerve instead of the musculocutaneous nerve. From a branchthat divides from the main trunk of the median nerve at nearly the middle of thearm a motor branch again divided that innervated the brachialis muscle anda sensory branch that conveyed the sense of the lateral part of the forearm.Furthermore, it was found that the brachial artery divided into its terminal branch-es, the radial and ulnar arteries. We believe that this rare variation of the mediannerve will shed light upon surgical procedures involving the median nerve.Key words: musculocutaneous nerve, median nerve, unusualinnervationINTRODUCTIONSince the brachial plexus is a structure in whichseveral spinal nerves unite and divide, variations itsformation are common [1, 8, 9]. There are, howev-er, few reports of the absence of the terminal branch-es of the brachial plexus [8].Normally the lateral cord gives its first branch,the lateral pectoral nerve, to the pectoralis majormuscle and then divides into the musculocutaneousnerve and the lateral root of the median nerve. Thelateral root of the median nerve then joins the medi-al root from the medial cord to form the mediannerve, which lies anterior to the third part of theaxillary artery [9].The anatomical abnormalities and variations ofthese nerves of the brachial plexus have recentlybecome significant because of new imaging tech-niques such as computed tomography and magneticresonance imaging. Moreover, investigation of thesevariants is important in order to define the anatom-ical features of each in relation to clinical diagnosisand for surgical procedures.RESULTSIn our study it was established that the musculo-cutaneous nerve was absent from the left arm ofa 58-year-old male formalin-fixed cadaver of theAnatomy Laboratory of Ondokuz Mayis Medical Fac-ulty. We first determined that the musculocutane-ous nerve did not divide from the lateral cord andthen that it was in fact absent. A nerve connectionleaving the lateral cord divided in front of the bra-chial artery, uniting the lateral and medial cords andthe lateral cord and ulnar nerve separately.By hyperabducting the upper extremity it was foundthat the medial and lateral fascicles of the median nerveunited 6 cm distal to a line passing from the coracoidprocess to the lower border of the second costa andthat the point of convergence was at the level of theinsertion of the pectoralis major muscle to the229M.E. Aydin et al., Absence of the musculocutaneous nerve together with unusual innervation of the median nerveThe median nerve gave out a branch which di-vided from it 8 cm inferior to the junction of thecords and this branch coursed its way to the fore-arm. Two nerves that divided from this branch in-nervated the brachialis muscle. This branch becamesuperficial just inferior to a line connecting theFigures 1A and B. Photograph showing the musculocutaneous nerve to be absent and an unusual in-nervation of the median nerve. 1 — median nerve; 2 — unusual innervation of the coracobrachialismuscle; 3 — nerve connection between the lateral and medial cords; 4 — brachial artery;5 — an unusual innervation of the lateral part of the forearm; 6 — biceps brachii muscle;7 — ulnar nerve.humerus (Fig. 1A). At a distance 0.5 cm inferior to thepoint of union a branch left the median nerve whichinnervated the coracobrachialis muscle. Another branchof the median nerve, which divided from it 2 cm infe-rior to the point of union, was found to be innervatingthe biceps brachii muscle (Figs. 1B, 2).AB230Folia Morphol., 2006, Vol. 65, No. 3medial and lateral epicondyles, providing the lateralpart of the skin innervation of the forearm.The major terminal branch of the median nervepassed deep to the two heads of the pronator teresmuscle at the cubital fossa and continued its wayand the innervation at the forearm. At a distance7.5 cm inferior to the line connecting the medial andlateral epicondyles the brachial artery, a neighbourof the median nerve, divided into its terminal branch-es, the radial and ulnar arteries. This differed fromthe usual point of division.DISCUSSIONNormally the musculocutaneous nerve is given offopposite the lower border of the pectoralis minor mus-cle. It pierces the coracobrachialis muscle and descendslaterally between the biceps and the brachialis musclesto the lateral side of the arm. Just below the elbow itpierces the deep fascia laterally to the tendon of theFigure 2. Drawing based on a photograph of dissected left arm and forearm. The axillary artery has beenremoved to show the nerves and axillary artery clearly. 1 — median nerve; 2 — the unusual innervationof the coracobrachialis muscle; 3 — the nerve connection between the lateral cord and medial cords;4 — brachial artery; 5 — the unusual innervation of the lateral part of the forearm; 6 — biceps brachiimuscle; 7 — ulnar nerve; 8 — ulnar artery; 9 — radial artery.Figure 3. Illustration of six types of musculocutaneous and median nerve and our case showed withan asterisk (*). LF — lateral cord; MF, medial cord; MC — musculocutaneous nerve; U — ulnar nerve;M — median nerve; CB — coracobrachialis muscle; BB — biceps brachii muscle; B — brachialismuscle; CC — the nerve connection between the lateral cord and the medial cord; LR — lateral rootof the median nerve; MR — medial root of the median nerve.biceps muscle and continues as the cutaneous nerve ofthe forearm [9]. Subsequently, in its course through thearm, it supplies the coracobrachialis, biceps brachii andthe greater part of the brachialis muscles [6].Bergman provided a list of variations in the courseand distribution of the musculocutaneous nerve. Hereported that this nerve arose from the lateral cord(90.5%), from the lateral and posterior cords (4%),from the median nerve (2%), as two separate bun-dles from the medial and lateral cords (1.4%) or fromthe posterior cord (1.4%). Moreover, he reported thatit might be doubled, unusually short or absent [2].In our case the musculocutaneous nerve wasfound to be absent. Absence of the nerve was alsoreported by Le Minor, Gumusburun and Adiguzel,Ihunwo et al., Bergman, Sud and Song [2–5, 8, 9].Nakatani et al., [7] Le Minor [5], Gumusburun andAdiguzel [3] also reported the absence of the mus-culocutaneous nerve (Fig. 3). In particular Sud’s case231M.E. Aydin et al., Absence of the musculocutaneous nerve together with unusual innervation of the median nervewas similar to this present instance in that the mo-tor nerve to the muscles of the anterior compart-ment of the arm arose from the median nerve.Le minor classified the variations of musculocuta-neous and median nerves into five types [5] (Fig. 3).The present case, however, was of a specific typeand did not fall within any of these five categories.In this case there is a nerve connection between themedial and lateral cords which originates from thelateral cord with two bundles and relies on the me-dial cord to unite themAnother finding in our case was that the cutane-ous innervation of the lateral part of the forearmwas procured by a thick nerve which divided fromthe median nerve. Our case differed from previouscases in two different features. One was the unusu-al innervation of the forearm muscles by the mediannerve, while the other was the unusual cutaneousinnervation of the lateral part of the forearm by themedian nerve.A further interesting finding was that the bra-chial artery, which is a neighbour of the mediannerve, divided into its terminal branches, the radialand ulnar arteries, 7.5 cm inferior to the line con-necting the medial and lateral epicondyles. Normallythe brachial artery commences at the lower marginof the tendon of the teres major and passes downthe arm, ending about 1 cm below the bend of theelbow, where it divides into the radial and ulnararteries [6]. Our case introduced for us the notionof a genuine absence of the musculocutaneousnerve rather than that of a conjoined form with thecourse of the median and the musculocutaneousnerves uniting.Knowledge of anatomical variations in the bra-chial plexus such as the absence of the musculocu-taneous nerve and of muscles that are innervated byunusual nerves may help clinicians faced with inde-cipherable clinical signs. This kind of case may pro-vide additional explanation for the unexpected clin-ical symptoms that depend on different nerve coursesand origins. Our case includes not only rare nervevariations but also an arterial variation. We believethat these will be illuminating for surgical procedures.REFERENCES1. Bergman R, Afifi AK, Miyauchi (2004) Median nerve.Illustrated Encyclopedia of Human Anatomic Variation.Opus III: Nervous System: Plexuses.2. Bergman R, Afifi AK, Miyauchi R (2004) Musculocuta-neus nerve. Illustrated Encyclopedia of Human Ana-tomic Variation. Opus III: Nervous System: Plexuses.3. Gumusburun E, Adiguzel E (2000) A variation of the bra-chial plexus characterized by the absence of the musculo-cutaneus nerve: a case report. Surg Radiol Anat, 22: 63–65.4. Ihunwo AO, Osinde SP, Mukhtar AU (1997) Distribu-tion of median nerve to muscles of the anterior com-partment of the arm. Cent Afr J Med, 43: 359–360.5. Le Minor JM (1990) A rare variation of the median andmusculocutaneus nerves in man. Arch Anat HistolEmbryol, 73: 33–42.6. Lewis WH (ed.) (2000) Anatomy of the human body(written by Gray H). 20th Ed. New York: Bartleby.com.On-line edition, section 6b the anterior divisions para-graphs: 51,61, section 4b brachial artery paraghraph 1.7. Nakatani T, Shigenori T, Mizukami S (1997) Absenceof the musculocutaneus nerve with innervation of co-racobrachialis, biceps brachii, brachialis and the later-al border of the forearm by branches from the lateralcord of the brachial plexus. J Anat, 191: 459–460.8. Song WC, Jung HS, Shin C, Lee BY, Koh KS (2003)A variation of the musculocutaneous nerve absent.Yonsei Med J, 44: 1110–1113.9. Sud M (2000) Absence of the musculocutaneous nerveand innervation of coracobrachialis, biceps brachii andbrachialis from the median nerve. J Anat Soc India,49: 176–177.

Absence of the musculocutaneous nerve together with unusual innervation of the median nerve

https://journals.viamedica.pl/folia_morphologica/article/download/16088/12726

Absence of the musculocutaneous nerve together with unusual innervation of the median nerve

Abstract

Similar works

Full text

Available Versions

Via Medica Journals