Case Report

International Journal of Anatomical Variations (2013) 6: 188–190eISSN 1308-4038

Proximal entrapment of median nerve associated with axillary artery variation: a case report

IntroductionThe median nerve is formed in the axilla by the union of the two roots as medial and lateral roots from medial and lateral cords of the brachial plexus, respectively. The nerve is formed lateral to the axillary artery, and the medial root of the nerve crosses from lateral to medial anterior to third part of the axillary artery superficially. In the arm the median nerve crosses anterior to the brachial artery from lateral to medial side, and enters the cubital fossa along with the brachial artery. The axillary artery gives three branches from its third part, namely anterior circumflex, posterior circumflex and subscapular artery. Lateral thoracic is a branch from second part of the axillary artery. Profunda brachii artery is a large branch from the posterior aspect of the brachial artery, which runs in the spiral groove.

Case ReportDuring a routine gross anatomy dissection of the axilla and upper limb in an adult male cadaver, the right limb revealed an unusual presentation of median nerve entrapment associated with several atypical branching patterns of the axillary artery.

Though, median nerve was indeed formed by two roots. The medial root of the median nerve emerged anterior to the third part of the axillary artery and posterior to variant artery, profunda brachii artery that arose directly and independently from the third part of the axillary artery; thereby leading to a rare case of high up proximal entrapment of the median nerve in the form of medial root compression by adjacent vascular structures (Figure 1).In the arm, the median nerve was unusually related to the posterior aspect of the brachial artery, it retained its normal anatomical relation from the cubital fossa onwards for the rest of the right upper limb (Figure 2). Concomitantly, the axillary artery also revealed a conjoint origin of the lateral thoracic artery, and subscapular artery. The latter gave off posterior circumflex humeral, circumflex scapular arteries and continued as thoraco-dorsal artery (Figure 3). In addition, third part of the axillary artery gave origin to anterior circumflex humeral and a variant artery, profunda brachii artery.The structures maintained their respective normal anatomical relations in the rest of the right forearm and hand. Meticulous dissection of the left upper limb revealed no aberrant anatomical relations.

Maitreyee NANDI KAR [1]

Chinmaya KAR [2]

Department of Anatomy [1], Emergency Medical Officer [2], North Bengal Medical College & Hospital, Sushrutanagar, Siliguri, West Bengal, INDIA.

Dr. Maitreyee Nandi (Kar) Assistant Professor Department of Anatomy North Bengal Medical College Sushrutanagar , Siliguri West Bengal, 734012, INDIA. +91 9433281801 drmkar1@yahoo.com

Received August 12th, 2012; accepted March 13th, 2013

AbstractDuring routine dissection of axilla and upper limb of a male cadaver, median nerve and third part of axillary artery showed variation in the right side. Though different variations of the median nerve have been reported, we have found a unique variation in the form of entrapment of medial root of median nerve by adjacent vascular structures. The median nerve was related to posterior aspect of brachial artery in the arm. Furthermore, the third part of axillary artery also showed variation of its branches. The embryological and clinical importance of these variations has also been discussed.© Int J Anat Var (IJAV). 2013; 6: 188–190.

Key words [anatomical variation] [median nerve] [axillary artery]

Published online November 27th, 2013 © http://www.ijav.org

189Entrapment of median nerve

DiscussionVariation in the median nerve is not very uncommon. It has been reported to be formed by four roots [1, 2], by three roots

–two from lateral cord and one from medial cord [2], and third root is also known to be contributed by the musculocutaneous nerve [3]. Median nerve has been found to be formed in the arm [2], medial to axillary artery [2, 4], posterior to axillary artery [5] and posterior to brachial artery [2, 4–6]. But entrapment of the medial root of the median nerve in between two vascular structures (axillary artery and profunda brachii artery) have not yet been reported. In our case, the median nerve itself was posteriorly related to brachial artery.These variations can be explained embryologically. The upper limb buds lie opposite to the lower five cervical and upper two thoracic segments. As soon as buds form, the ventral primary rami of the spinal nerves penetrate into the mesenchyme of limb bud and establish intimate contact with differentiating mesodermal condensations. The early contact between nerve and muscle cell is a prerequisite for their complete functional differentiation [7, 8]. The variations could arise from circulatory factors at the time of fusion of brachial plexus cord. In human, the forelimb muscles develop from the mesenchyme of the para-axial mesoderm during fifth week of embryonic life [8]. The axon of spinal nerve grows distally to reach the limb bud mesenchyme. The peripheral processes of the motor and sensory neurons grow in the mesenchyme in different directions. Once formed, any developmental differences would obviously persist postnatally [7]. As the guidance of the developing axons is regulated by expression of chemo-attractants and chemo-repellants in a highly coordinated site-specific fashion, any alteration in signaling between mesenchymal cells and neuronal growth cones can lead to significant variations [9].This rare form of high up proximal median nerve entrapment in the form of medial root compression may lead to neurovascular symptoms such as numbness. This knowledge

Figure 1. Figure shows entrapment of medial root of median nerve by adjacent vascular structures. (1: lateral root of median nerve; 2: medial root of median nerve; 3: trunk of median nerve; 4: axillary vein; 5: profunda brachii artery; 6: axillary artery)

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Figure 2. Figure shows variant relation of median nerve and brachial artery in arm. (3: median nerve; 7: brachial artery)

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Figure 3. Figure (a) and illustration (b) showing the origin of combined trunk of lateral thoracic and subscapular artery from 3rd part of axillary artery. (8: common trunk of lateral thoracic and subscapular artery; 9: lateral thoracic artery; 10: subscapular artery; 11: posterior circumflex artery; 12: circumflex scapular artery; 13: thoracodorsal artery)

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190 Kar and Kar

of variation of median nerve may be beneficial in plastic and repair surgery as well as in diagnosis of median nerve compression. This variation of medial root of median nerve may be confused with more common causes of pain syndrome due to nerve entrapment such as radiculopathy and carpal tunnel syndrome.The variation of arteries of upper limb is common (11–24%) [10]. During embryogenesis the lateral branch of seventh cervical intersegmental artery becomes enlarged to form the axial artery of upper limb, which on further development becomes axillary, brachial, its bud gives rise to radial and ulnar arteries [11, 12]. The arterial variations in the upper limb are due to defects in embryonic development of the vascular plexus in the upper limb buds. This may be due to arrest at any stage of development of the vascular plexus showing regression, retention or reappearance and may lead to variations in the arterial origins and courses of the major upper limb vessels [13]. In a case series, subscapular artery has been reported to arise from a common trunk with posterior circumflex humeral artery up to 30% of cases [14]. Occasionally the subscapular, circumflex humeral and profunda brachii arteries arise in common, in which case branches of the brachial plexus surround this common vessel instead of axillary artery. In one study, presence of bilateral common subscapular-humeral trunk arising from the 3rd part and thoraco-humeral trunk from the 2nd part of axillary

artery has been reported. The latter gave lateral thoracic, subscapular, circumflex humeral and thoraco-dorsal arteries [15]. The variation of subscapular artery is not uncommon. The present case showed variant branching pattern of third part of axillary artery. The subscapular and lateral thoracic arteries arise from the third part of axillary artery and the former gave off posterior circumflex humeral, circumflex scapular and then continued as thoraco-dorsal artery (Figure 3). A case of atypical vascular pattern often associated with nervous variants indicates that segmental origin of axillary artery and its branching pattern may determine the arrangement of brachial plexus during fetal development.The present case showed combination of multiple variations

–entrapment of medial root of median nerve in between third part of axillary artery posteriorly and profunda brachii artery variant branch from the axillary artery anteriorly, altered relation of brachial artery and median nerve in arm, and variant branches from third part of axillary artery. The knowledge of this type of vascular variation may be of profound importance in diagnostic intervention as well as in surgical procedures like treating aneurysm of axillary artery, axillary artery hematoma, brachial plexus palsy, reconstruction of axillary artery after trauma, during surgery of breast augmentation, radical mastectomy, during surgical intervention of fractured upper end of humerus or dislocation of shoulder joint.

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