Variation in the Branching Pattern of the Axillary Artery

The branching pattern of the axillary artery (AXA) is commonly presented by subdividing it into three sections based on its location relative to the pectoralis minor muscle. Conveniently, each of these three parts has a corresponding number of branches (e.g., the first ‘part’ has one branch, the second has two). The thoracoacromial trunk usually arises deep to pectoralis minor, while the lateral thoracic artery (LTA) branches nearby and courses inferiorly along the superficial surface of the serratus anterior muscle. However, it is not uncommon for the LTA to be entirely absent and for a branch from the neighboring thoracodorsal artery (TDA) to serve as the blood supply to serratus anterior. Here, we investigated the frequency of LTAs branching directly from the AXA versus the TDA, and documented any unusual patterns. We studied 92 previously dissected upper extremities from 48 cadavers housed at Midwestern University (Downers Grove, IL) during the 2015–16 academic year (not all cadavers could be assessed bilaterally). The LTA branched directly from the AXA in 45 limbs (49%), 30 (33%) had branches originating from the TDA, and 6 (~6%) had vessels arising from the subscapular artery prior to the branching of the circumflex scapular artery. The remaining 11 limbs displayed unique variations, including one type that was noted multiple times. In these cases, a large vessel branched just proximal to where the AXA passed inferior to pectoralis minor and ran subparallel to the AXA (i.e., the vessel that ultimately continued as the brachial artery). The AXA gave off no further named branches while the unnamed, parallel branch gave rise to most of the major axillary vessels before bifurcating into the anterior and posterior circumflex humeral arteries. There was a nearly 50/50 chance of observing the LTA branching directly from the AXA or one of the above variants on any given limb in our cadaver population. These results differed significantly from a previous study that identified the LTA branching from the AXA 78% of the time (Olinger and Benninger, 2010, Clinical Anatomy, 23[4]:407–12). Students of gross anatomy routinely learn neurovascular branches by the pattern presented in lectures, textbooks, and atlases, and may not pay close attention to the fact that these vessels are named by the tissue(s) they supply. To be sure, the concept of neurovascular variability is more readily discussed with regard to the blood supply of the abdominal viscera, for example, than that of the upper extremities. However, our study highlights that anatomical variation of this sort ought to be discussed earlier and more frequently – particularly in the gross anatomy laboratory – to better prepare students for variations they might encounter in both academic and clinical settings. Support or Funding Information We are grateful to the donors and the Anatomical Gift Association of Illinois; all donors and their families were aware that remains could be used for both educational and research pursuits. This research did not require IRB approval. We also wish to acknowledge funding support from Midwestern University's Dr. Kenneth A. Suarez Fellowship Program.