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Journal of the Anatomical Society of India

Anomalous Communications in the Branches of Brachial Plexus

Author(s): Gupta M, Goyal N, Harjeet

Vol. 54, No. 1 (2005-01 - 2005-03)

Postgraduate Institute of Medical Education and Research, Chandigarh.

Abstract:

Anatomical variations in the formation, course and distribution of brachial plexus are well documented but the presence of the various anomalies in the same limb is very rare. Numerous communications in the various terminal branches of the cords of brachial plexus were observed during routine dissection of upper limb of an adult male cadaver in the department of Anatomy, PGIMER, Chandigarh. In the left upper limb the lateral cord (LC) was formed in relation to the second part of axillary artery. As formation of LC was distal than usual, lateral pectoral nerve arose as two separate branches from the anterior divisions of upper and middle trunks instead of LC. A communication was observed between these lateral pectoral nerves. Anterior division of middle trunk also gave rise to the nerve to coracobrachialis and an additional lateral root of median. Lateral pectoral nerve arising from anterior division of middle trunk also communicated with the medial pectoral nerve by two communicating branches. A network of nerve fibers was also seen in between these two nerves. A pseudoganglion was present at the site of proximal communication between lateral and medial pectoral nerves. Communications were also found between i) additional lateral root of median and medial root of median ii) medial root of median and ulnar nerve iii) medial cutaneous nerve of arm and forearm iv) ulnar and radial nerve. The terminal branches of cords of brachial plexus usually do not communicate at numerous sites in the arm except for the formation of median nerve.

Keywords: Brachial plexus, cords, lateral pectoral

Introduction:

Anomalies of brachial plexus and its terminal branches are not uncommon and have been widely documented (Kerr, 1918; Hasan and Narayan, 1964; Hollinshead, 1958). The common and more obvious variation in brachial plexus is the level of its formation, the pre-fixed and post-fixed plexus. Variations may occur in the formation of trunks, divisions, cords and terminal branches. Division of trunks and formation of cords may be anomalous; however the arrangement of terminal branches remains unchanged (Moore and Dalley, 1999). According to Williams et al. (1995) the terminal branches of lateral and medial cords do not communicate in the arm. The present paper deals with the variations in the formation and branching pattern of lateral cord (LC) and the various anomalous communications between the terminal branches of the cords of brachial plexus.

Material & Methods:

Anomalies of brachial plexus were observed during routine dissection of left upper limb of 35 yrs adult male cadaver in the department of Anatomy, PGIMER, Chandigarh. The branches of lateral and medial cords of brachial plexus were carefully dissected and the variations from the usually described pattern were noted.

Results:

In the left upper limb the formation of LC was distal than usual, in relation to the second part of axillary artery behind the pectoralis minor muscle by the union of anterior division of upper trunk (d 1 ) and anterior division of middle trunk (d 2 ) of brachial plexus. Normally the divisions do not give any branches but in the present report lateral pectoral nerve arose as two separate branches (LPn 1 and LPn 2 ) from the anterior divisions of upper and middle trunks respectively. Anterior division of middle trunk also gave rise to the nerve to coracobrachialis and an additional proximal lateral root of median nerve. LC was formed by the union of 'd 1' and 'd 2', it then run lateral to axillary artery for 2.4cm and just below the level of origin of circumflex humeral arteries; it terminated as usual into musculocutaneous nerve and the usual lateral root of median nerve. No lateral pectoral nerve arose from the LC. Musculocutaneous nerve didn't supply any branch to coracobrachialis muscle but pierced the muscle as usual and later supplied the biceps and brachialis muscles. The branching pattern of medial cord of the brachial plexus was normal. However the median nerve was formed by the union of two lateral roots and one medial root. The proximal lateral root arose from the anterior division of the middle trunk while the distal lateral root was the usual terminal branch of the LC.

LPn 1 after its origin from 'd 1' run upwards and laterally and divided into five terminal branches just below the clavicle to supply the pectoralis major muscle. A communicating branch (c 1 ) arose from LPn 1 2cm distal to its origin and joined the LPn 2 1.5cm distal to its origin from 'd 2'.

LPn 2 after its origin from 'd 2' run laterally to supply the pectoralis major muscle. LPn 2 communicated with the medial pectoral nerve (MPn) by two twigs 'c 2' and 'c 3' which arose from LPn 1.7 cm and 2.3 cm distal to the communication 'c 1'. Communication between lateral and medial pectoral nerves was also seen on right side.

Medial pectoral nerve, a branch of medial cord, run laterally crossing the axillary artery and lateral root of median nerve anteriorly. The MPn received two communications 'c' and 'c' from the LPn 2 . A thickening like a pseudoganglion was present at the junction of 'c 2' and MPn. From this thickening numerous branches arose to supply the pectoralis minor muscle. An interesting observation was the presence of plexus between MPn and LPn 2 just lateral to the two communications. After forming the plexus, MPn followed the usual course to supply the pectoralis minor muscle (Figs. 1, 2, 3).

Multiple communications were also found between the other branches of lateral, medial and posterior cords. A communicating twig (c 4 ) arose from the proximal lateral root of median nerve and appeared to take a recurrent course running medially anterior to the axillary artery to join the medial root of median nerve. Another communicating branch (c 5 ) was present in between the medial root of median and ulnar nerve.

This communicating branch (c 5 ) arose from the medial root of median 8cm distal to its origin and run medially and slightly downwards for 0.9cm to join the ulnar nerve 2cm distal to its origin.

The medial cutaneous nerve of forearm 2.9cm distal to its origin gave a communicating branch (c 6 ) which run downward and laterally for 2.4cm to join the medial cutaneous nerve of arm 4.7cm distal to its origin.

Another communicating branch (c 7 ) arose from ulnar nerve 0.9cm distal to its origin and run downwards and laterally for 3cm to join the radial nerve (Figs. 3, 4).

None of the anomalous communications were observed in the right brachial plexus.

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Fig. 1: Photograph of dissected axilla showing left brachial plexus i) communication (C1) between two lateral pectoral nerves (LPn1 & LPn2) which are arising from divisions (d1 & d2) ii) communications (C2 & C3) between medial pectoral nerve (MPn) and LPn2. Note the presence of pseudoganglion (psgang) on MPn. NCb, nerve to coracobrachialis; LC, lateral cord; pMj, pectoralis major; PMn, pectoralis minor; AA, axillary artery.

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Fig. 2: Photograph of dissected axilla showing left brachial plexus i) Higher origin of nerve to coracobrachialis (NCb) from anterior divison ofupper trunk (d1). (Lateral cord (LC) has been displaced medially). d2, anterior division of middle trunk; LPn1, lateral pectoral nerve arising from 'd1'; MPn, medial pectoral nerve; PMj, pectoralis major; MCn, musculocutaneous nerve; Mn, median nerve; Un, ulnar nerve; AA, axillary artery; SH Biceps, short head of Biceps.

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Fig. 3: Photograph of dissected axilla showing various communications of left brachial plexus between i) C4, between additional lateral root of median nerve (LMa) & medial root of median (MM); ii) C5, between medial root of median & ulnar nerve (Un); iii) C7, ulnar nerve & radial nerve (Rn). Note the formation of median nerve (Mn) by union of three roots LMa, LMu & MM. d1, anterior divison of upper trunk; d2, anterior divison of middle trunk; LC, lateral cord; MC, medical cord; NCb, nerve to coracobrachalis; MPn, medial pectoral nerve; MCn, musculocutaneous nerve; MCF, medial cutaneous nerve of forearm; AA, axillary artery.

Discussion :

In left brachial plexus of 35year old male, numerous anomalies were observed like the branches arising from anterior divisions of upper and middle trunks, lower formation of LC, communications between lateral and medial pectoral nerves, presence of pseudoganglion on medial pectoral nerve and communications between terminal branches of cords. Kerr (1918) described the variations in the level of formation of medial and lateral cords and the distribution of branches of brachial plexus. In some individuals, trunk, division or cord formation may be absent; the lateral or medial cords may receive fibers from anterior divisions directly inferior or superior to the usual levels respectively (Moore and Dalley, 1999). In the present study the LC was formed distal than usual by the union of anterior divisions of upper and middle trunks in relation to the second part of axillary artery, behind the pectoralis minor muscle. The anterior division of upper trunk gave origin to the lateral pectoral nerve and the anterior division of middle trunk gave three branches the lateral pectoral nerve, nerve to coracobrachialis and an additional lateral root of median nerve.

Lateral pectoral nerve arose as two separate branches from the anterior divisions of upper and middle trunks. The two branches did not unite except for a communication and supplied the pectoralis major muscle individually. Hollinshead (1958) and Williams et al. (1995) also described that the lateral pectoral nerve may arise by one root from LC or by two roots from the anterior divisions of upper and middle trunks as was seen in the present study. Rao and Chaudhary (2001) observed two cases in which lateral pectoral nerve and nerve to coracobrachialis arose from LC as the musculocutaneous nerve was absent while Kerr (1918) described a case in which lateral pectoral nerve arose as two separate branches from the anterior divisions of upper and middle trunks similar to the present observation but did not observe the presence of any communication between the two branches.

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Fig. 4: Schematic representation of left brachial plexusshowing multiple communications in thebranchesof the cords. Note the anterior divison of upper trunk (d1) giving lateral pectoral nerve (LPn1)& anterior division of middle trunk (d2) giving 3branches lateral pectoral nerve (LPn2), nerve tocoracobrachialis (NCb) & additional lateral root ofmedian (LMa). C2, communication between LPn1& LPn2; C2 & C3, communications between LPn2 and MPn; C4, communication between LMa & MM; C5, communications between medial root of median & ulnar nerve; C6, communications between medial cutaneous nerve of arm & forearm; C7, communications between ulnar & radial nerve; LC, lateral cord; MC, medial cord; MPn, medial pectoral nerve; MCn, musculocutaneous nerve; Mn,median nerve; MM, medial root of median; LMu, usual lateral root of median; MCA, medial cutaneous nerve of arm; MCF, medial cutaneous nerve of forearm; Un, ulnar nerve; Rn, radial nerve; Psgang,pseudoganglion; PMj, pectoralis major; PMn, pectoralis minor.

The lateral pectoral nerve which arose from anterior division of middle trunk also communicated by numerous branches to the medial pectoral nerve. At the site of this communication on the medial pectoral nerve a pseudoganglion like thickening was observed before it supplied the pectoralis minor muscle. Williams et al. (1995) also described that the lateral pectoral nerve sends a ramus to the medial pectoral nerve forming a loop in front of the first part of the axillary artery.

Formation of median nerve by two lateral and one medial root is reported earlier (Chauhan and Roy, 2002; Saeed and Rufai, 2003) and the communications between musculocutaneous and median nerve are also well documented (Yang et al., 1995; Chiarapattanakom et al., 1998; Choi et al., 2002). Venieratos and Anagnostopoulou (1998) in their work on brachial plexus stated that communication between musculocutaneous and median nerve is the most frequent of all the variations that could be observed in the brachial plexus but in the present study communication was present between the medial and lateral roots of median nerve and not between the median and musculocutaneous nerves.

Communications were also seen in the branches of the medial and posterior cords, as the medial root of median nerve gave a communicating twig to the ulnar nerve which could be the fibers that median root of median received from the lateral root as described by Hollinshead (1958). He stated that ulnar nerve usually receives fibers from seventh cervical nerve by receiving a contribution from the LC. Iyer and Fenichel (1976), Gutmann (1977), Crutchfield and Gutmann (1980) and Snock et al. (1991) reported the communication between median and ulnar nerve in forearm and hand. The communication between ulnar and radial nerve is not well documented.

High origin of nerve to coracobrachialis from LC is reported by Flatow et al. (1989), Williams et al. (1995), Nakatani et al. (1997), Gümüsburun and Adigüzel (2000) and Sarikcioglu et al. (2001). However in the present report it arose from the anterior division of the middle trunk as the formation of the cord was distal than normal and musculocutaneous nerve pierced the coracobrachialis without giving any branch to the muscle.

These variations of the cords of brachial plexus and its terminal branches become important during surgical exploration of the axilla and arm region to avoid damage to the important nerves (Abhaya et al., 2003). All these variations documented in literature were observed in an adult which is very unusual.

Acknowledgements:

The authors wish to thank Mr. Vijay Bakshi, Senior artist of Anatomy department for the illustrations.

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