Aberrant Dual Origin of the Dorsal Scapular Nerve and Its Communication with Long Thoracic Nerve: An Unusual Variation of the Brachial Plexus

Abstract

During a routine dissection of the posterior triangle of the neck (right side) on a male cadaver, a variation related to the dorsal scapular nerve and long thoracic nerve was encountered. After firm identification of the variation, the region was dissected to reveal the full details of the course of dorsal scapular and long thoracic nerve, and the variation was photographed using an 8 megapixel digital camera. An atypical formation of dorsal scapular nerve [Table/ Fig-1] was seen, in the posterior triangle of the neck. The dorsal scapular nerve (DSN) which usually comes from the C5 root, had contributions from C5 and the C6 roots. The C5 component of the DSN pierced the scalenus medius muscle and divided into two branches within the muscle. The bigger branch ended by supplying the levator scapula muscle, while a smaller branch continued downwards and joined with a branch arising from the C6 root. On further dissection, it was found out that the two branches from the C5 and C6 roots united and coursed down as main trunk of dorsal scapular nerve. On the contrary, it was observed that the long thoracic nerve was formed by two components C6, C7 [Table/ Fig-1] mainly instead of three ventral rami of C5, C6, C7 cervical nerves. The C5 component of the long thoracic nerve was not apparently seen, but a communicating branch was given from C6 which seemed to carry fibres from C5. The C7 component was seen to arise from the middle trunk, which is a continuation of the ventral rami of the C7 spinal nerve. The C6 nerve root pierced the scalenus medius muscle and divided within the muscle into two smaller branches. The larger branch coursed down to join the C7 component of the long thoracic nerve (LTN), while the smaller branch coursed down to join a branch from the C5.Further, the brachial plexus as a whole was prefixed with contribution from the ventral rami of the 4 th cervical nerve [Table/ Fig-1], thus the upper trunk formed by the union of the C5 and C6 was thick and long. The Erbs point was identified and the nerve to subclavius and suprascapular nerves were also seen.A band of muscle fibers was further observed to connect the middle portion of the scalenus medius with the scalenus anterior muscle Pre and post-fixed variations at roots of the brachial plexus have been well documented, however little is known about the variations that exist in the branches which arise from the brachial plexus. In this paper, we describe about one such rare variation related to the dorsal scapular and the long thoracic nerve, which are the branches arising from the roots of the brachial plexus. The variation was found during routine dissection. The dorsal scapular nerve, which routinely arises from the fifth cervical nerve root (C5), was seen to receive contributions from C5 as well as sixth cervical nerve (C6), while the long thoracic nerve arose from C6 and seventh cervical nerves (C7) only. Furthermore along with variations in origin of the dorsal scapular and long thoracic nerves, the brachial plexus was seen to exist as a prefixed ...

A Cadaveric Investigation of the Dorsal Scapular Nerve

“…Lee et al (1992) reported that nearly 25% of the DSNs in their study originated from other spinal nerve roots aside from C5 [ 14 ] whereas Tubbs et al (2005) reported that 95% of the DSNs originated from C5 and 5% branched from C5 and C6 [ 10 ]. A recent study by Shilal et al (2015) also documented that the DSN arose from C5 and C6 and receives communications with the long thoracic nerve [ 15 ]. In addition, there are varying reports regarding the muscles that DSN innervates.…”

The Aberrant Origin of the Suprascapular Artery May Hide Neural Covariants: A Cadaveric Finding

“…In the current case, the piercing of the middle scalene muscle by the anterior ramus from the C6 spinal nerve may cause a partial LTN compression, resulting in reduced severity of the symptoms of pain, paresthesia, and/or paresis [ 10 ]. Shilal et al [ 11 ] reported an interconnection of the LTN with the dorsal scapular nerve (originating from the C5 and C6 spinal nerves). Concerning the functional anatomy, the LTN innervates the serratus anterior muscle (a broad and flat muscle that functions as a force pair alongside the trapezius and rhomboid muscles), providing stable anchoring of the scapula to the chest wall.…”

Topographic and morphometric anatomy of the proximal part of the dorsal scapular nerve

“…Ballesteros and Ramirez (2007) reported that 17 (30.4%) of 56 DSN shared a common branch with LTN. In the case report study of Shilal et al (2015), it was reported that unilateral DSN has an aberrant communicating branch with LTN. Williams and Smith's study (Williams & Smith, 2020) found that the DSN and the LTN share a common branch in 3 (4.05%) of 74 DSNs.…”

“…In addition to C5, various sources have also reported involvement from the anterior branch of the C4 spinal nerve (Moore et al, 2018; Netter, 2014; Schuenke et al, 2014; Tubbs et al, 2016). However, anatomical studies in the literature have reported various variations on this subject (Ballesteros & Ramirez, 2007; Hanson & Auyong, 2013; Lee et al, 1992; Nguyen et al, 2016; Shilal et al, 2015; Tubbs et al, 2005; Williams & Smith, 2020).…”

“…It has been stated in the studies that the DSN and the LTN may have a common branch (Ballesteros & Ramirez, 2007; Shilal et al, 2015; Williams & Smith, 2020). Considering the importance of these nerves in maintaining the scapulohumeral rhythm and the high frequency of entrapment, to understand the etiology of shoulder and interscapular region pain and scapular winging, the relationship of these nerves may be important (Sultan & Younis El‐Tantawi, 2013; Williams & Smith, 2020).…”