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 Table of Contents  
ORIGINAL ARTICLE
Year : 2022  |  Volume : 11  |  Issue : 2  |  Page : 79-83

Anatomy of lateral pectoral nerve and its clinical significance


1 Associate Professor, Department of Anatomy, Government TD Medical College, Alappuzha, Kerala, India
2 Assistant Professor, Department of Anatomy, Government Medical College, Trivandrum, Kerala, India
3 Associate Professor, Department of Anatomy, Government Medical College, Kollam, Kerala, India

Date of Submission24-Jan-2022
Date of Decision01-Mar-2022
Date of Acceptance14-Mar-2022
Date of Web Publication26-May-2022

Correspondence Address:
C Manju Madhavan
Department of Anatomy, Government TD Medical College, Alappuzha, Kerala
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/NJCA.NJCA_23_22

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  Abstract 


Background: Anatomy of the pectoral nerves is very important for surgeons who plan pectoral nerve grafts, breast augmentation surgeries, and radical mastectomies. The correlates given in literature are contradictory in nature. Hence, a study was planned to elucidate the anatomy of lateral pectoral nerves (LPNs). Methodology: 40 pectoral regions of embalmed cadavers were dissected. Number, location, length, diameter, branches, and distribution of the LPN were noted. They were grouped according to the number and pattern of origin. Results: Two LPN were found in 77.5% of the specimens, with origins from the lateral cord of brachial plexus either from a common point (45%) or separately (32.5%). Superior LPN (SLPN) was closely related to cephalic vein, had a mean length of 4.7 cm, diameter of 1.9 mm and had two branches supplying clavicular head of pectoralis major. A shorter SLPN of average length 1.55 cm was noted when it pierced the pectoralis minor muscle proximally (32.5%). Inferior LPN (ILPN) was closely related to thoracoacromial vessels, had a mean length of 3.6 cm, diameter 1.7 mm and had two branches, one supplying sternocostal head of pectoralis major and the other communicating with medial pectoral nerve. In 95% of the specimens, both these nerves could be identified just below the clavicle, at the junction between its middle and lateral thirds. In cases with single LPN (7 specimens), it branched into SLPN and ILPN. Conclusion: The anatomy of LPN is variable and important while exploring the pectoral region during surgeries.

Keywords: Brachial plexus, lateral pectoral nerve, pectoralis major, pectoralis minor


How to cite this article:
Madhavan C M, Rajasekharan S, Varghese S. Anatomy of lateral pectoral nerve and its clinical significance. Natl J Clin Anat 2022;11:79-83

How to cite this URL:
Madhavan C M, Rajasekharan S, Varghese S. Anatomy of lateral pectoral nerve and its clinical significance. Natl J Clin Anat [serial online] 2022 [cited 2022 Jul 4];11:79-83. Available from: http://www.njca.info/text.asp?2022/11/2/79/346074




  Introduction Top


The anatomy of pectoral nerves is gaining surgical importance with increasing practice of pectoral nerve blocks, breast augmentation surgeries, and nerve transfers. Pectoral nerve blocks are given to relieve spastic pain after mastectomies and for surgery in the pectoral region. Pectoral nerves can be used as grafts in repair of brachial plexus injuries distal to their origin.[1] The outcome of the breast augmentation surgery is better when the implant is sub-pectotal and with denervated pectoral muscles.[2] These advances in breast surgeries command a thorough knowledge of the region including pectoral nerves and their variations. The pectoral nerve anatomy is highly variable. Scant reports explaining the pectoral anatomy complicate a detailed understanding.

There are contradictions regarding the number and nomenclature of pectoral nerves. Classically, they are named lateral and medial, based on their origins (from lateral and medial cords of the brachial plexus respectively). The lateral pectoral nerve (LPN) is described as a single nerve in all standard text books. However, in recent studies, three pectoral nerves are described-superior, middle and inferior, where superior and middle represent LPN (2 numbers) and inferior represents medial pectoral nerve.[3] There are no uniform guidelines for surgical identification of these nerves.

With this background, this study is undertaken with the objective to elucidate the anatomy of LPN in terms of number, location, course, relations, branches, and distribution.


  Materials and Methods Top


In a descriptive study, 40 pectoral regions were dissected from 20 embalmed cadavers (18 males and 2 females) after obtaining clearance from the Institutional Ethical Committee (IEC.No. 02/11/2016/MCT). The sample size was calculated using the following formula n = (Z1−α) pq/d2 where p is the lowest percentage of variation in origin of lateral pectoral nerve which is 10% according to Prakash KG et al.[4] Since the sample size thus calculated was too large to be feasible, it was planned as a census type study for a duration of 2 years. All the cadavers used for routine dissection in that period were included in this study thus making the sample size 40 (including both sides).

Dissection of the region was done as described in Cunningham's manual of practical anatomy.[5] After reflecting the skin of the pectoral region, the superficial and deep fasciae over pectoralis major (PM) were removed. Then, the clavicular and sternocostal heads of the muscle were detached from their origins and the muscle was reflected laterally. The plane between the two pectoral muscles and clavipectoral fascia were carefully dissected and the lateral pectoral nerves (LPNs) were identified. The nerves were cleaned without injuring epineurium to avoid misinterpretation of data. The point of emergence of nerves in relation to inferior border of clavicle, its origin, course and distribution were studied with arms partially abducted. The presence, mode of formation, and position of ansa pectoralis were noted. The lengths of the nerves from their origin to the point of entrance to the muscle and their diameters were measured using a Vernier caliper.[6] The specimens were grouped according to the number of LPN observed [Figure 1]. Group 1 with only one LPN, Group 2 with 2 LPN, and Group 3 with more than 2. Group 2 was further subdivided into sub group “a” (with a common point of origin) and “b” (where the points of origin were separated). The data were entered in excel format and statistical analysis done. Mean with standard deviation and proportions were calculated.
Figure 1: Schematic diagram showing grouping of lateral pectoral nerves and their relation with clavicle. SPLN: Superior lateral pectoral nerve, ILPN: Inferior lateral pectoral nerve, MCL: Midclavicular line, NL: Line passing through the junction of middle and lateral thirds of clavicle

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  Results Top


There were two LPN (Group 2) in 77.5% of specimens (31 out of 40). Among these, except in two specimens, both nerves originated from lateral cord of brachial plexus. In two specimens, they arose from anterior divisions of upper and middle trunks. In 18 specimens belonging to Group 2, the nerves were found originating from a single point (Group 2a), whereas in 13 specimens, the point of origins were separated by a distance ranging from 2 mm to 1 cm (Group 2b). As the distance between the origins increased, the upper one became more medial in position and was seen superior to the termination of cephalic vein [Figure 2]. When they had a common origin, the two nerves could be identified below the termination of cephalic vein [Figure 3]. In specimens belonging to Group 1, the nerve was seen inferior to cephalic vein.
Figure 2: Group 2b (2 LPN with separate origins from lateral cord). SPLN: Superior lateral pectoral nerve, ILPN: Inferior lateral pectoral nerve, CV: Cephalic vein, AV: Axillary vein, AA: Axillary artery, Pm: Pectoralis minor, PM: Pectoralis major, TAA: Thoraco acromial artery

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Figure 3: Group 2a (2 LPN with same point of origin from lateral cord). SPLN: Superior lateral pectoral nerve, ILPN: Inferior lateral pectoral nerve, CV: Cephalic vein, AV: Axillary vein, AA: Axillary artery, Pm Pectoralis minor, PM: Pectoralis major

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The LPN could be identified just below the inferior border of clavicle at the junction of its middle and lateral thirds in 95% of specimens. In the specimens where the origins were from trunks of brachial plexus, they could be identified just below the midpoint of the clavicle. The LPN observed will be termed here as superior and inferior LPN (SLPN and ILPN) according to their position in pectoral region and course.

In Group 2 specimens, SLPN, after its origin, pierced clavipectoral fascia immediately related to cephalic vein and entered the clavicular part of PM after a short course plastered to its deep surface. In 25% of specimens of Group 2b and in all of Group 2a, it was seen inferior to the cephalic vein, whereas in 75% of Group 2b, it was found superior to the vein. The length of the nerve depended on the origin and point of entry to the muscle. In 67.75% of cases where it had a subfascial course deep to the muscle, its length ranged from 3 cm to 7 cm with a mean value of 4.8 cm. However, in 32.25% cases, it pierced the muscle more proximally so that its length ranged from 1.02 cm to 2.32 cm with a mean value of 1.35 cm. In Group 2b, where they had a separate origin from lateral cord, the mean length was slightly greater by about 0.69 cm. The thickness was almost same in both groups. Mean values with standard deviations for each group are given in [Table 1].
Table 1: Length and diameter of lateral pectoral nerves in different groups

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The ILPN was found closely related to thoraco-acromial vessels and entered the sternocostal part of PM along with its pectoral branches. It usually gave one branch near its origin which communicated with the medial pectoral nerve. This communication was over the second part of axillary artery in 72. 5% which was identified as ansa pectoralis. Sometimes, it was distal and plastered to the deep surface of pectoralis minor (Pm) muscle. The main nerve had a mean length of 4.05 ± 0.166 cm and diameter of 1.8 ± 0.166 mm in both Group 2a and 2b. In 25% of specimens, its branches formed plexus with medial pectoral nerve beneath Pm and branches from this plexus pierced the muscle to supply PM [Figure 4]. Mean values with standard deviations for each group are given in [Table 1].
Figure 4: Inferior Lateral pectoral nerve forming plexus with medial pectoral nerve. Pm: Pectoralis minor

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In Group 1 (7 specimens), there was only one LPN which divided into two branches after a course of about 1–2 cm. Course of the branches resembled that of SLPN and ILPN found in Group 2. The branch of communication arose from the trunk near its origin. The length of the upper branch was comparable to that of SLPN, whereas lower branch was shorter by about 0.5 cm when compared to the ILPN. The diameters of branches were found to be slightly less when compared to the corresponding nerves of Group 2.

There were four specimens belonging to Group 3. Of these, 3 specimens had 3 LPN and one had 5 LPN, all arising from the single point from lateral cord. In all these specimens, the first branch resembled SLPN. The others followed the course of ILPN. In one specimen with 3 LPN, lower two nerves were on either side of thoracoacromial artery and instead of ending in the sternocostal head of PM, they pierced Pm after communicating with medial pectoral nerve.


  Discussion Top


Both pectoral muscles have dual nerve supply from lateral and medial pectoral nerves. Upper clavicular part of PM muscle is supplied by LPN with a root value of C5, C6, and C7. The lower sternocostal part is supplied by medial pectoral nerve (C8 and T1). There are contradictions to this spinal origin. Some studies argue that C6 gives contribution to lateral and medial pectoral nerves,[7] whereas some found C7 contributing to both.[8] Whichever way, sharing of spinal segments makes them ideal candidates for grafts because it will cause only minimum functional deficit.[9] LPN is used in nerve transfer surgeries in injuries of spinal accessory nerve and supra scapular nerve due to its proximity to these nerves.[10],[11]

Even though a single LPN arising from lateral cord as described in textbooks was the major finding in some studies,[4],[12],[13] majority of studies found two LPN.[1],[3],[6],[14],[15] When double, the origins were mostly from upper and middle trunks. However, a small percentage of single LPN arising from either upper trunk[14],[16] or middle trunk[17] or with two roots from both trunks,[3],[4],[18],[19] is also described. In a meta-analysis presented by Porzionato et al.,[10] it is shown that 33.8% of LPN described in the literature are double and arise from the trunk, whereas 23.4% is single and arises from lateral cord of brachial plexus. Nomenclature also varies. In many articles, the traditional naming of pectoral nerves as medial and lateral according to their origins from cords of brachial plexus is not followed. They name the pectoral nerves as superior middle and inferior, where superior and middle represents the LPN and inferior represents the medial pectoral nerve.[1],[3],[6] We preferred to name the two LPN as superior and ILPN, thus indicating their origin from lateral cord. In about 78% of our specimens, we could identify two LPN, originating from lateral cord of brachial plexus. 58% of them had single point of origin. In others they were separated by a distance of 1 mm to 2 cm. Position of SLPN and its relation to cephalic vein depended on this distance. It became more medial in position and superior to the cephalic vein as the distance increased. We could not find any article which describes the relation of LPN to cephalic vein. However, this relation is important due to the chance of injury to the vein during nerve harvesting.

The position of the nerve in relation to bony points is a key factor in surgical anatomy but is seldom represented in the studies of LPN. Some studies describe the position of the nerve in relation to the midsternal line.[4] However, as this may differ in people with different skeletal frames, its position in relation to the junction of middle and lateral thirds of clavicle (which can be easily identified due to the change in shape of the bone), is more dependable. We found that when the LPN had a common origin from the lateral cord or when it appeared as a single nerve, it was usually seen just below this point. However, when the nerves have separate origins, the SLPN was seen more toward the mid clavicular line. When the nerves arise from the trunks, both nerves are seen near mid clavicular line posterior to clavicle. The position of LPN is described as close to midclavicular line in some studies.[2],[6],[16] In an article still in press, Boer et al.[14] describe the position of SLPN just lateral to midclavicular line and that of ILPN below the lateral one-third of the line joining acromioclavicular joint to sternoclavicular joint. Our study agrees with this finding.

Aszmann et al.[1] describe the branching pattern of LPN. He describes two branches each from superior and inferior LPN. The inferior nerve has superficial and deep branches. Superficial branch supplies clavicular and upper sternal parts of PM. The deep branch is seen plastered to the deep surface of Pm. It communicates with medial pectoral nerve to form nerve plexus and its branches pierce Pm muscle and supplies sternocostal part of PM. In our study, we found two branches for SLPN which supplied clavicular part of PM which agrees with the above-mentioned study. However, in most of the specimens the ILPN, after giving a communication branch to the medial pectoral nerve, supplied Pectoralis major without piercing the Pm muscle. However, in about 25% of specimens, we found similar plexus beneath Pm muscle. The same finding is also described by Prakash et al.[4] and Goel et al.[20] Branching pattern of the nerve is important while planning graft surgeries. If it forms plexus, the effective length of the graft will be reduced.

In a meta-analysis on anatomy of Pm muscle, Asghar et al.[21] mentions the course and distribution of lateral pectoral nerve also. They dwell upon the variations in origin of LPN, formation of ansa pectoralis and its distribution to Pm. According to them, LPN supplies Pm muscle and has cutaneous distribution below clavicle. Only 25% of our specimens showed branches to Pm muscle and we have not found any cutaneous branches from lateral pectoral nerve. We found ansa pectoralis over the axillary artery only in 72.5% specimens in contrast with the observation in the above study (77%).

The length and diameter of LPN are studied in detail by David et al.[6] In their study in fresh cadavers, the mean length of superior lateral pectoral nerve is 6.5 cm and that of inferior lateral pectoral nerve is 11 cm. However, the length and diameter of LPN observed in our study were less. This may be because of the fact that our study was done in embalmed cadavers. Exposure to formalin may have caused the contracture of the tissue. The length of the SLPN was slightly more in specimens where the origins of the two LPN were separate. Furthermore, we observed that, in about 32.25% of specimens, the length of SLPN was very less with a mean value of 1.35 cm (when it pierced the muscle proximally). This is not described in literature to our knowledge. These findings should be kept in mind while planning nerve graft surgeries.

Variations in number of LPN are also described. Rai et al.[22] describe three LPN whereas Padur et al. describe a specimen in which lateral pectoral nerve was absent.[23] We also found three specimens with 3 LPN and one with 5 LPN.

The use of LPN in nerve transfers and grafts is described in many articles.[6],[9],[10] Maldonado et al.[11] describe supraclavicular approach to harvest LPN to anastomose with spinal accessory nerve, based on the fact that most common level of origin of LPN are from trunks of brachial plexus. However, in our study, most LPNs were found to be arising from the lateral cord of brachial plexus below the clavicle. This should be kept in mind while planning such surgeries in South Indian population.


  Conclusions Top


There are variations in the anatomy of LPN. They are usually two in number (SLPN and ILPN), arising from the lateral cord of brachial plexus and are seen just below the junction of middle and lateral thirds of clavicle. They are closely related to cephalic vein and thoracoacromial vessels. SLPN supply clavicular part and ILPN supply sternocostal part of PM. If LPN is single, it branches into SLPN and ILPN. Only 25% of LPN have direct branches to Pm. However, 72.5% specimens showed ansa pectoralis over the second part of the axillary artery where it communicated with the medial pectoral nerve. They are motor nerves seen in the predictable position and can be spared. This makes them ideal candidates for grafts. Surgeons should be aware of their variations to avoid accidental injuries.

Acknowledgment

The authors sincerely thank those who donated their bodies to science so that anatomical research could be performed. Results from such research can potentially increase humankind's overall knowledge that can then improve patient care. Therefore, these donors and their families deserve our highest gratitude.[24]

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Aszmann OC, Rab M, Kamolz L, Frey M. The anatomy of the pectoral nerves and their significance in brachial plexus reconstruction. J Hand Surg Am 2000;25:942-7.  Back to cited text no. 1
    
2.
Hoffman GW, Elliott LF. The anatomy of the pectoral nerves and its significance to the general and plastic surgeon. Ann Surg 1987;205:504-7.  Back to cited text no. 2
    
3.
David S, Balaguer T, Baque P, Peretti FD, Valla M, Lebreton E, et al. The anatomy of the pectoral nerves and its significance in breast augmentation, axillary dissection and pectoral muscle flaps. J Plast Reconstr Aesthet Surg 2012;65:1193-8.  Back to cited text no. 3
    
4.
Prakash KG, Kuppasad S. Anatomical study of pectoral nerves and its implications in surgery. J Clin Diagn Res 2014;8:C01-5.  Back to cited text no. 4
    
5.
Koshi R. Cunningham's Manual of Practical Anatomy. 16th ed., Vol. 1. United Kingdom: Oxford University Press; 2017.  Back to cited text no. 5
    
6.
David S, Balaguer T, Baque P, Lebreton E. Transfer of pectoral nerves to suprascapular and axillary nerves: An anatomic feasibility study. J Hand Surg Am 2010;35:92-6.  Back to cited text no. 6
    
7.
Moore KL, Dalley AF. Clinically Oriented Anatomy. 5th ed. Philadelphia: Lippincott Williams & Wilkins; 2006. p. 773-81.  Back to cited text no. 7
    
8.
Lee KS. Anatomic variation of the spinal origins of lateral and medial pectoral nerves. Clin Anat 2007;20:915-8.  Back to cited text no. 8
    
9.
Stockinger T, Aszmann OC, Frey M. Clinical application of pectoral nerve transfers in the treatment of traumatic brachial plexus injuries. J Hand Surg Am 2008;33:1100-7.  Back to cited text no. 9
    
10.
Porzionato A, Macchi V, Stecco C, Loukas M, Tubbs RS, De Caro R. Surgical anatomy of the pectoral nerves and the pectoral musculature. Clin Anat 2012;25:559-75.  Back to cited text no. 10
    
11.
Maldonado AA, Spinner RJ. Lateral pectoral nerve transfer for spinal accessory nerve injury. J Neurosurg Spine 2017;26:112-5.  Back to cited text no. 11
    
12.
Moosman DA. Anatomy of the pectoral nerves and their preservation in modified mastectomy. Am J Surg 1980;139:883-6.  Back to cited text no. 12
    
13.
Chaudhary P, Singla R, Arora K, Kalsey G. Formation and branching pattern of cords of brachial plexus – A cadaveric study in north Indian population. Int J Anat Res 2014;2:225-33.  Back to cited text no. 13
    
14.
Boers N, Bleys RL, Schellekens PP. The nerve supply to the pectoralis major: An anatomical study and clinical application of the denervation in subpectoral breast implant surgery. J Plast Reconstr Aesthet Surg 2022;75:415-23.  Back to cited text no. 14
    
15.
Beheiry EE. Innervation of the pectoralis major muscle: Anatomical study. Ann Plast Surg 2012;68:209-14.  Back to cited text no. 15
    
16.
Shetty P, Nayak SB, Kumar N, Thangarajan R, D'Souza MR. Origin of medial and lateral pectoral nerves from the supraclavicular part of brachial plexus and its clinical importance – A case report. J Clin Diagn Res 2014;8:133-4.  Back to cited text no. 16
    
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Gupta M, Goyal N, Kaur H. Anomalous communications in the branches of brachial plexus. J Anat Soc India 2005;54:22-5.  Back to cited text no. 17
    
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Kerr AT. The brachial plexus of nerves in man, the variations in its formation and branches. Am J Anat 1918;23:285-395.  Back to cited text no. 18
    
19.
Fazan VP, Amadeu AD, Caleffi AL, Filho OA. Brachial plexus variations in its formation and main branches. Acta Cir Bras 2003;18:1-8.  Back to cited text no. 19
    
20.
Goel S, Rustagi SM, Kumar A, Mehta V, Suri RK. Multiple unilateral variations in medial and lateral cords of brachial plexus and their branches. Anat Cell Biol 2014;47:77-80.  Back to cited text no. 20
    
21.
Asghar A, Naaz S, Naya S. The prevalence and distribution of the variants of pectoralis minor in cadaveric studies: A systematic review and meta-analysis of 32 observational studies. Natl J Clin Anat 2021;10:164-73.  Back to cited text no. 21
  [Full text]  
22.
Rai R, Ranade AV, Prabhu LV, Pai MM, Nayak SR. Accessory lateral pectoral nerves supplying the pectoralis major. Rom J Morphol Embryol 2008;49:577-9.  Back to cited text no. 22
    
23.
Padur AA, Kumar N, Shanthakumar SR, Shetty SD, Prabhu GS, Patil J. Unusual and unique variant branches of lateral cord of brachial plexus and its clinical implications – A cadaveric study. J Clin Diagn Res 2016;10:C01-4.  Back to cited text no. 23
    
24.
Iwanaga J, Singh V, Ohtsuka A, Hwang Y, Kim HJ, Moryś J, et al. Acknowledging the use of human cadaveric tissues in research papers: Recommendations from anatomical journal editors. Clin Anat 2021;34:2-4.  Back to cited text no. 24
    


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