Origin of Medial and Lateral Pectoral Nerves from the Supraclavicular Part of Brachial Plexus and its Clinical Importance – A Case Report

Knowledge of normal and anomalous formation of brachial plexus and its branches is of utmost importance to anatomists, clinicians, anesthesiologists and surgeons. Possibility of variations in the origin, course and distribution of branches of brachial plexus must be kept in mind during anesthetizing the brachial plexus, mastectomy and plastic surgery procedures. In the current case, the medial pectoral nerve arose directly from the middle trunk of the brachial plexus and the lateral pectoral nerve arose from the anterior division of the upper trunk of the brachial plexus. The lateral pectoral nerve supplied the pectoralis major and the medial pectoral nerve supplied pectoralis major and pectoralis minor muscles through two separate branches.

During routine dissection classes for medical undergraduates, we observed anomalous branches of supraclavicular part of the brachial plexus. The upper trunk was formed by the union of the C5 and C6 ventral rami; the middle trunk by continuation of C7 ventral ramus and the lower trunk by the union of C8 and T1 ventral rami. Each trunk divided into anterior and posterior divisions. The upper trunk gave its normal branches; suprascapular nerve and nerve to subclavius. The anterior division of the upper trunk gave origin to the lateral pectoral nerve, which ran down behind the middle of the clavicle to reach the pectoral region. In the pectoral region it entered the deeper surface of the pectoralis major muscle and supplied it [Table/Fig-1,2]. The middle trunk gave origin to the medial pectoral nerve which ran down behind the middle of the clavicle to reach the pectoral region. Further, it divided into two branches, one each for pectoralis major and pectoralis minor muscles [Table/Fig-1,2].

[Table/Fig-1]:

Dissection of the lower part of the right side of the neck showing the trunks of brachial plexus (UT – upper trunk; MT – middle trunk; LT – lower trunk; SA – subclavian artery; PD – posterior division of the upper trunk; AD – anterior division of the upper trunk; SSN – suprascapular nerve; LPN – lateral pectoral nerve; MPN – medial pectoral nerve; PN – phrenic nerve; IJV – internal jugular vein; TCA – transverse cervical artery)

[Table/Fig-2]:

Dissection of the lower part of the right side of the neck and pectoral region showing the anomalous origin of the medial and lateral pectoral nerves (UT – upper trunk; MT – middle trunk; LT – lower trunk; LPN – lateral pectoral nerve; MPN – medial pectoral nerve; PMJ – pectoralis major; PMN – pectoralis minor)

Brachial plexus is the major nerve plexus that supplies the upper limb. It presents roots, trunks, divisions, cords and branches.Its upper trunk gives 2 branches called suprascapular nerve and nerve to subclavius. According to the text book descriptions, neither the middle and lower trunks nor the divisions of any of the three trunks give any branches in the posterior triangle[1]. Many previous studies have reported the variations in the formation and branching pattern of the trunks. Formation of the upper trunk by the union of C5, C6 and C7 roots has been reported by Nayak et al., [2]. In a study by Uysal et al., [3] the upper trunk was absent in 1% of cases and the lower trunk was absent in 9% of cases. Their study also reported the formation of the upper trunk by C4 and C5 roots and the lower trunk by T1 and T2 roots. Matejcik [4] has reported the fusion of upper and middle trunks bilaterally.

Neurovascular blockage of medial and lateral pectoral nerves is done in some clinical procedures such as mastectomy to reduce post-operative pain and in shoulder dislocations caused by spasm of pectoralis major muscle, to reduce the muscle spasm [5-7]. Knowing the exact topography of these nerves and their possible variations can contribute tremendously to the success of these procedures. The knowledge of variations of pectoral nerves is also important for plastic surgeons and head and neck surgeons because pectoral nerve denervation may be helpful in decreasing the pain and spasm in the head and neck surgery and also the pectoralis major myocutaneous flap is one of the most frequently used flaps in head and neck reconstruction [8]. The lateral pectoral nerve may arise from the lateral cord or from the anterior divisions of the upper and middle trunks [9]. Gupta et al., [10] have reported the origin of two lateral pectoral nerves as two separate branches from the anterior divisions of upper and middle trunks.Its origin from the posterior division of the upper trunk has been reported by Singhal et al., [11]. In the same study, they noted the origin of medial pectoral nerve directly from the C6 root. Origin of three lateral pectoral nerves from lateral cord has been reported by Rai et al., [12]. Solomon et al.,[13] have reported a case where the lateral pectoral nerve supplied the deltoid muscle bilaterally. Medial pectoral nerve variations are less frequent than the lateral pectoral nerve and reports on its variations are scanty. Union of intercostobrachial nerve with the medial pectoral nerve has been reported by Loukas et al., [14]. Mehta et al., [15] have reported the multiple branches of medial pectoral nerve piercing the pectoralis minor and supplying the pectoralis major muscle. Medial pectoral nerve was a direct branch of the anterior division of the middle trunk in a study by Fazan et al., [16]. The origin of medial pectoral nerve directly from the middle trunk of brachial plexus has not been reported hitherto.

The origin of the lateral and medial pectoral nerves from the supracalavicular part of brachial plexus is very rare and is clinically important. Knowledge of the same may be very useful in repairing the fractures of the clavicle, raising a pectoralis major flap in plastic surgeries, dealing with the spasmoidic dislocation of the shoulder and while performing mastectomy.

[1]. WH Hollinshead, General survey of the upper limb In: Hollinshead WH. Anatomy for surgeons. Vol. 3: The back and limbs 1958 New YorkA Hoeber–Harper Book:225-45.  [Google Scholar]

[2]. S Nayak, SN Somayaji, VR Vollala, D Raghunathan, V Rodrigues, VP Samuel, PA Malloor, A rare variation in the formation of the upper trunk of the brachial plexus - a case report Neuroanatomy 2005 (4):37-38.  [Google Scholar]

[3]. II Uysal, M Seker, AK Karabulut, M Buyukmumcu, T Ziylan, Brachial plexus variations in human fetuses Neurosurgery 2003 53(3):676-84.  [Google Scholar]

[4]. V Matejcik, Anatomic variations in the brachial plexus trunks and nerve roots Rozhl. Chir 2003 456(9):67-90.  [Google Scholar]

[5]. GW Hoffman, LF Elliott, The anatomy of the pectoral nerves and its significance to the general and plastic surgeon Ann Surg 1987 205:504-07.  [Google Scholar]

[6]. R Layeque, J Hochberg, E Siegel, K Kunkel, J Kepple, RS Henry-Tillman, Botulinum toxin infiltration for pain controlafter mastectomy and expander reconstruction Ann Surg 2004 240:608-13.  [Google Scholar]

[7]. A Sinha, DW Higginson, A Vickers, Use of botulinum A toxin in irreducible shoulder dislocation caused by spasm of pectoralis major J Shoulder Elbow Surg 1999 8:75-76.  [Google Scholar]

[8]. D Cunha-Gomes, C Choudhari, NM Kavarana, Vascular compromise of the pectoralis major musculocutaneous flap in head and neck reconstruction Ann Plast Surg 2003 51:450-54.  [Google Scholar]

[9]. KS Lee, Anatomical variation of the spinal origins of lateral and medial pectoral nerves Clin Anat 2007 20:915-18.  [Google Scholar]

[10]. M Gupta, N Goyal, Harjeet Anomalous communications in the branches of brachial plexus J Anat Soc India 2005 54(1):22-25.  [Google Scholar]

[11]. S Singhal, W Rao, R Ravindranath, Variations in brachial plexus and the relationship of median nerve with the axillary artery: a case report J Brachial Plex Peripher Nerve Inj. 2007 :2-21.  [Google Scholar]

[12]. R Rai, AV Ranade, LV Prabhu, MM Pai, SR Nayak, Accessory lateral pectoral nerves supplying the pectoralis major Romanian Journal of Morphology and Embryology 2008 49(4):577-79.  [Google Scholar]

[13]. LB Solomon, N Ravindranath, B Vidic, M Dym, Anatomical variant of the lateral pectoral nerve innervating the anterior portion of the deltoid muscle: a case report Anat Rec 1997 249(4):506-09.  [Google Scholar]

[14]. M Loukas, J Grabska, RS Tubbs, RJ Louis, Jr. An unusual union of the intercostobrachial nerve and the medial pectoral nerve Folia Morphol (Warsz) 2007 66(4):356-9.  [Google Scholar]

[15]. V Mehta, R Baliyan, J Arora, RK Suri, G Rath, A Kumar, Unusual innervation pattern of pectoralis minor muscle-anatomical description and clinical implications Clin Ter 2012 163(6):499-502.  [Google Scholar]

[16]. V Fazan, A Amadeu, A Calaffi, C Felio, Brachial Plexus variations in its formation and main branches Acta Cirurgica Brasileisa 2001 18(5):14-18.  [Google Scholar]