Dorsal Scapular Artery Variations and Relationship to the Brachial Plexus, and a Related Thoracic Outlet Syndrome Case

Abstract

Rationale Knowledge of the relationship of the dorsal scapular artery (DSA) with the brachial plexus is limited. Objective We report a case of a variant DSA path, and revisit DSA origins and under-investigated relationship with the plexus in cadavers. Methods The DSA was examined in a male patient and 106 cadavers. Results In the case, we observed an unusual DSA compressing the lower plexus trunk, that resulted in intermittent radiating pain and paresthesia. In the cadavers, the DSA originated most commonly from the subclavian artery (71%), with 35% from the thyrocervical trunk. Nine sides of eight cadavers (seven females) had two DSA branches per side, with one branch from each origin. The most typical DSA path was a subclavian artery origin before passing between upper and middle brachial plexus trunks (40% of DSAs), versus between middle and lower trunks (23%), or inferior (4%) or superior to the plexus (1%). Following a thyrocervical trunk origin, the DSA passed most frequently superior to the plexus (23%), versus between middle and lower trunks (6%) or upper and middle trunks (4%). Bilateral symmetry in origin and path through the brachial plexus was observed in 13 of 35 females (37%) and 6 of 17 males (35%), with the most common bilateral finding of a subclavian artery origin and a path between upper and middle trunks (17%). Conclusion Variability in the relationship between DSA and trunks of the brachial plexus has surgical and clinical implications, such as diagnosis of thoracic outlet syndrome.

Keywords: anatomical variations; brachial plexus; dorsal scapular artery; subclavian artery; thoracic outlet syndrome; thyrocervical trunk.

Fig. 1

Sagittal T2-weighted, water-only imaging, corresponding to the coronal T2 image. The hypointense branching structure indicated by the arrow is the putative dorsal scapular artery branching off the subclavian artery, which is impinging on the proximal C8 root. MRI acquisition was performed on GE (Waukesha, Wisconsin, United States) 3T magnet using the IDEAL sequence. Water-only images are presented. Acquisition was performed with T _E = 60 ms and T _R = 7,907 ms.

Fig. 2

Impingement of the lower trunk of the brachial plexus by the dorsal scapular artery (DSA) in a case report of a 17-year-old male. (A) The phrenic nerve (indicated with a small black arrow) and trunks of the brachial plexus were exposed and identified. The phrenic nerve is passing over the lower trunk of the brachial plexus. The C8 ventral ramus contribution to the lower trunk was found to be impinged by a DSA that was 2 mm in diameter and that originated from the subclavian artery. This DSA crossed superior to the C8 ventral ramus just prior to the merger of the C8 and T1 ventral rami to form the lower trunk. (B) The artery was ligated and divided to relieve the C8 impingement.

Fig. 3

Varied paths of the dorsal scapular artery (DSA) between the trunks of the brachial plexus in four different representative cadaveric specimens. (A) The DSA (arrowhead) in this cadaver originates from the thyrocervical trunk rather than from the subclavian artery (SCA). It next passes anterior to the scalenus anterior (SA) muscle (although it often passes inferior to this muscle) and superior to the brachial plexus. (B) In a different cadaver, the DSA (indicated with an arrow) originates from subclavian artery (SCA) before passing between the upper and middle trunks of the brachial plexus. Tr, trunk. (C) In another cadaver, the DSA (arrow) originates from subclavian artery before passing between the middle and lower trunks of brachial plexus. This cadaveric example is most like the case shown in Figs. 1 and 2. (D) Two DSA branches were observed in some cadavers. In these cadavers, one of the DSA branches typically originated from the thyrocervical trunk (white arrowhead) before taking a path superior to the brachial plexus (black arrowhead). The second DSA branch (arrow) typically arose from the subclavian artery (SCA). Each DSA branch in these cadavers traveled to a similar location deep to the rhomboid muscles.