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| OJHAS Vol. 15, Issue 4:
(October-December 2016) |
Case Report
Concurrent Variations of Lateral Pectoral, Median, and Musculocutaneous Nerves
Authors
Satheesha B Nayak, Melaka Manipal Medical College (Manipal Campus),
Manipal University, Manipal, Karnataka State, India,
Swamy Ravindra S, Melaka Manipal Medical College (Manipal Campus), Manipal University, Manipal, Karnataka State, India
Naveen Kumar, Melaka Manipal Medical College (Manipal Campus), Manipal University, Manipal, Karnataka State, India,
Srinivasa Rao Sirasanagandla, Department of Human and Clinical Anatomy, College of Medicine and Health Sciences, Sultan Qaboos University,
Muscat, Al Khudh 123, Oman,
Abhinitha P, Melaka Manipal Medical College (Manipal Campus), Manipal University, Manipal, Karnataka State, India,
Ashwini Aithal P, Melaka Manipal Medical College (Manipal Campus), Manipal University, Manipal, Karnataka State, India,
Surekha D Shetty, Melaka Manipal Medical College (Manipal Campus), Manipal University, Manipal, Karnataka State, India.
Address for Correspondence
Surekha D Shetty,
Melaka Manipal Medical College (Manipal Campus),
Manipal University,
Manipal -576104,
Udupi District, Karnataka State,
India.
E-mail:
ds.surekha@gmail.com
Citation
Nayak SB, Swamy RS, Kumar N, Rao SS, Abhinita P, Aithal AP, Shetty SD. Concurrent Variations of Lateral Pectoral, Median, and Musculocutaneous Nerves. Online J Health Allied Scs.
2016;15(4):11. Available at URL:
http://www.ojhas.org/issue60/2016-4-11.html
Submitted: Nov 23,
2016; Accepted: Dec 30, 2016; Published: Jan 31, 2017 |
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Abstract:
Brachial plexus frequently presents variations of its cords and branches. We saw concurrent variations of lateral pectoral, median and musculocutaneous nerves. There were two lateral pectoral nerves. Median nerve was formed by the union of 3 roots; two lateral roots and one medial root. Medial root arose from the ulnar nerve. Musculocutaneous nerve did not pierce the coracobrachialis muscle. There was a thick communicating branch between the musculocutaneous and median nerves. Though there are reports on individual variations mentioned above, it is very rare to see all of them in the same individual. Knowledge of these variations may be handy in axillary lymph node clearance and performing nerve blocks.
Key Words:
Lateral pectoral nerve, median nerve, musculocutaneous nerve, brachial plexus |
Introduction
Brachial plexus is the nerve plexus that supplies the nerves to the upper limb.
Its supraclavicular part is situated in the neck and the infracalvicular part in the axilla. Infraclavicular
part consists of cords and branches of the brachial plexus. Many variations of the cords and branches of the
brachial plexus have been reported already. Lateral pectoral nerve usually arises from the lateral cord and
supplies the pectoralis major and minor muscles. Generally it does not pierce the pectoralis minor muscle.
Sometimes, the lateral pectoral nerve arises from the supraclavicular part of the brachial plexus.[1] Median
nerve is usually formed by union of its lateral and medial roots arising from lateral and medial cords of
brachial plexus respectively. Occasionally, median nerve possesses more than two roots.[2,3]
Musculocutaneous nerve is a branch of lateral cord of brachial plexus and rarely does it fail to pierce the
coracobrachialis muscle.[4] Various communicating branches between median and musculocutaneous nerve have also
been reported.[5] We report the combination of all above said variations in a single cadaver and discuss their
possible clinical implication.
Case Report
During dissection classes for medical students, we noticed multiple variations in the left brachial plexus of an adult male cadaver aged about 75 years. There were two lateral pectoral nerves. They arose from the lateral cord of brachial plexus. One of them entered the pectoralis major muscle after passing above the upper border of the pectoralis minor muscle; while the other entered the pectoralis major muscle after piercing the pectoralis minor muscle (Figures 1 and 2). The medial root of median nerve arose from the proximal part of the ulnar nerve. The lateral root was thin and it arose from the lateral cord. After crossing the axillary artery from lateral to medial side, it divided into two roots. These two roots joined the medial root to form the median nerve, medial to the axillary artery (Figures 1 and 2). Thus the median nerve had three roots in total. Musculocutaneous nerve did not pierce the coracobrachialis muscle. The proximal part of the median nerve was thinner than the proximal part of the musculocutaneous nerve. There was a thick communicating branch between the musculocutaneous and median nerves in the distal part of the axilla. Through this communicating branch, about 50% of fibres of musculocutaneous nerve were given to the median nerve.
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Figure 1. Photograph of neatly dissected infraclavicular part of left brachial plexus.
(SBC – subclavius muscle; PMI – pectoralis minor muscle; PMJ – pectoralis major muscle; BB – biceps brachii muscle; CB – coracobrachialis muscle; AV – axillary vein; AA – Axillary artery; AN – axillary nerve; LPN – duplicated lateral pectoral nerve; RMN – Three roots of the median nerve; MPN – medial pectoral nerve; MCN – musculocutaneous nerve; MN – median nerve; CB – communicating branch between musculocutaneous and median nerves; UN – ulnar nerve; MCNF – medial cutaneous nerve of forearm)
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Figure 2. Photograph of closer view of the left brachial plexus.
(SBC – subclavius muscle; PMI – pectoralis minor muscle; PMJ – pectoralis major muscle; AV – axillary vein; AA – Axillary artery; AN – axillary nerve; LPN – duplicated lateral pectoral nerve; RMN – Three roots of the median nerve; MPN – medial pectoral nerve; MCN – musculocutaneous nerve; MN – median nerve; UN – ulnar nerve; MCNF – medial cutaneous nerve of forearm; RN – radial nerve; MC – medial cord of brachial plexus; LC – lateral cord of brachial plexus)
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Discussion
The current case draws attention due to the
existence of multiple variations of branches of brachial plexus. In most of the
individuals, usually there will be a single lateral pectoral nerve and rarely
does it pierce the pectoralis minor muscle. Though higher origin and duplication
of lateral pectoral nerve is seen occasionally, it is very rare to see it
piercing the pectoralis minor muscle. In the current case, one among the two
lateral pectoral nerves pierced the pectoralis minor muscle before reaching the
pectoralis major muscle. The knowledge of variations of lateral pectoral nerve
is essential for surgeons during breast reconstruction after mastectomy and also
in axillary lymph node clearance.[6] It is also advisable to be aware of
variations of the pectoral nerves during the cosmetic surgeries of breast and
raising a myocutaneous flap for reconstructive surgeries of head and neck.[7,8]
Median nerve normally has two roots of origin but more than two roots of origin and low origin have been reported already.[3,4] Origin of the median nerve in the current case differs from the earlier reported cases mainly because its medial root arose from the ulnar nerve. Axillary artery being crossed by the lateral root, division of lateral root into two branches and formation of median nerve medial to the axillary artery also make the case more interesting. Anaesthesiologists performing nerve blocks, surgeons performing resections of neoplasms and dealing with trauma of the axilla are advised to be aware of this variation of the median nerve.
Musculocutaneous nerve may be totally absent [9], may not pierce coracobrachialis [4] and may give communicating branches to nearby nerves in the axilla.[10] In the current case, the nerve did not pierce the coracobrachialis but its branches and distribution was normal. The eye catching feature of the musculocutaneous nerve in this case is that major part of it continued into the median nerve as the communicating branch. This communicating branch contributed about 50% of the total thickness of the median nerve beyond the axilla. Injury to this branch can result in significant sensory and motor loss in the upper limb.
Conclusion:
Though individual variations of lateral pectoral, median and musculocutaneous nerves have been reported as individual cases, reports on combined variations of all the three are lacking. Origin of medial root of the median nerve from ulnar nerve is the unique feature of this case. Knowledge of these variations can be very important for surgeons while cleaning axillary lymph nodes and performing reconstructive and cosmetic breast surgeries. It is also of importance to plastic surgeons and anaesthesiologists.
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