INTRODUCTION
The subclavian artery continues lateral to the first rib as the axillary artery (AA) where it is divided into three distinct parts as it relates to the pectoralis minor muscle. The first part of the AA is proximal to the pectoralis minor and typically gives off only one branch, the superior thoracic artery (STA). As the AA travels in its second part, posterior to the pectoralis minor, it normally provides two branches: the thoracoacromial trunk (TAT) and the lateral thoracic artery (LTA). Finally, distal to the pectoralis minor muscle, the third part of the AA typically gives three branches: the anterior humeral circumflex artery (AHCA), posterior humeral circumflex artery (PHCA), and subscapular artery (SA). The SA then typically quickly bifurcates into the circumflex scapular artery (CSA) and the thoracodorsal artery (TDA). As the AA passes the inferior border of teres major its name changes to brachial artery which continues in the arm.
While the muscles of the shoulder girdle can receive collateral circulation from numerous sources, the study of arterial branching remains important because these major arteries maintain close anatomical relationships with the brachial plexus. The cords of the brachial plexus are named based on their relationship to the second part of the AA; their close proximity suggests that arterial variation in this region can pose a risk for neuropathy as seen by previous anatomical and clinical case studies [16, 22]. An understanding of possible anatomical variations can help guide surgical and therapeutic procedures.
While AA variations are not uncommon, the current case discusses a rare variation in which the first part of the right AA provides a novel common trunk (CT). This aberrant CT gave origin to the following branches: an accessory LTA (aLTA), an accessory (aTDA), the SA and the PHCA (Table 1) [1–3, 14, 18–20, 22]. The aim of this case study is to provide a detailed case presentation of this unique branching pattern of the AA while outlining possible clinical implications of this variant.
|
AA parts |
Typical branching pattern |
Current variation branching pattern |
Reported variants branching patterns |
|
First |
STA |
LTA TAT CT: aLTA, aTDA, PHCA, SA |
TAT and SA (described in the Discussion) [14] |
|
Second |
TAT LTA |
Pectoral artery |
SA gave the LTA and PHCA [20] |
|
CT for the SA and LTA [18] |
|||
|
Third |
SA: CSA and TDA PHCA AHCA |
AHCA |
Common subscapular trunk was the origin for the SA, AHCA and PHCA [22] |
|
CT bifurcated into the PHCA and S [19] |
|||
|
A common subscapular trunk provided the CSA, TDA, PHCA, LTA, TAT [3] |
|||
|
A CT divided into the deep brachial artery, AHCA, PHCA, SA [1] |
|||
|
A CT divided into the SA and a common stem for the AHCA, PHCA and the deep brachial artery [2] |
CASE REPORT
The body of a 77-year-old female was received by the Saint Louis University Gift Body Programme of the Center for Anatomical Science and Education (CASE) with the informed consent of the donor. The death certificate listed hepatic carcinoma as the cause of death. No other pathologies were noted.
Dissection of the right axilla was completed according to instructions outlined in Grant’s dissector, 16th Edition [7]. After the right axillary vein was cleaned and studied, it was removed to better study the AA branching pattern. One unique variation observed in the right AA included the absence of a traditional STA originating from the first part of the AA. Instead, from proximal to distal, the first part of the AA gave three branches: the LTA, the TAT, and a large CT. After providing these three branches, the AA continued distally, deep to the pectoralis minor and surrounded by the lateral, posterior, and medial cords of the brachial plexus. Proximally, the LTA provided the STA to the first and second intercostal spaces before continuing with the long thoracic nerve to supply the serratus anterior muscle (Fig. 1).
The large CT branched into an aLTA to the serratus anterior muscle and a large aTDA to the latissimus dorsi muscle. These named branches were identified based on the muscles they supply but are described as accessories because they originate from an atypical source. The CT then bifurcated into the PHCA and the SA. The PHCA travelled with the axillary nerve, while the SA bifurcated into a CSA and a small TDA (Fig. 2).
The second part of the AA provided one pectoral artery to the pectoralis minor. The third part of the AA supplied the AHCA artery before continuing as the brachial artery (Fig. 3). Normally, the AA is closely approximated by the three cords of the brachial plexus. However, in this unique case, the AA and CT surrounded the medial cord and the medial antebrachial cutaneous nerve (Fig. 3). The branching pattern of this variant AA is summarized in a sketch depicting the branches from each part of the AA (Fig. 4). The left AA and upper extremity venous drainage were anatomically typical.
DISCUSSION
Previously documented AA variations
A wide variety of AA variations have been documented in the literature, including the presence of common arterial trunks which give rise to branches that normally originate directly from the AA [5, 6]. In addition to the typical origin of the SA and PHCA from the third part of the AA, these two vessels have been observed arising from a CT from either the first or second part of the AA [11]. The current case adds another distinct finding to this description with the higher origin of a CT from the first part of the AA.
A study of 166 axillae described the branching pattern of the LTA, SA, and PHCA finding that the LTA gave rise to both the TDA and the SA in about 10% of the cases while the PHCA was observed to variably originate from either the SA or the deep brachial artery in about 20% of the cases [15]. The current case adds to the description of the possible origins of the SA and PHCA as arising from a CT from the first part of the AA. Another case study describes two branches, the TAT and SA, arising from the first part of the AA, with the SA providing the LTA before terminating as the TDA and PHCA [14]. However, the current case has three branches originating from the first part of the AA. The CT in our report provided both an aLTA and an aTDA before bifurcating into the SA and PHCA artery.
Furthermore, the current case includes an LTA that quickly provides the STA, a branching pattern which is rarely seen. The current literature regarding reported anomalous STA origins and trajectories includes one case study in which the STA originates from the first part of the AA but travels between components of the brachial plexus to reach the lateral thoracic wall [1]. A second case report includes two cadaveric dissections where the LTA originated cephalad to the STA along the first part of the AA [25].
The presence of a large CT from the first part of the AA that supplies an aLTA and an aTDA, before bifurcating into the PHCA and SA, has not been reported in the literature. Table 1 [1–3, 14, 18–20, 22] outlines descriptions of documented AA branching patterns as they compare to the current case.
Clinical significance
It has been reported that the AA has the highest rate of arterial injury after the popliteal artery, so it is of great clinical significance for radiologists and surgeons to be aware of its possible variations [1, 3, 13, 15, 17–20, 22, 24]. Carotid-axillary bypass is an alternative to carotid-subclavian bypass due to the significant lymphatic risks that can occur in the latter procedure, but variations in the AA branching pattern can introduce new risks [4]. Furthermore, the current case reveals the PHCA artery originating from a CT rather than from the most distal portion of the AA. Both the AHCA and PHCA (as well as the deep brachial artery) are significant when repairing rotator cuff and proximal humeral injuries as the arteries anastomose around the surgical neck of the humerus [8, 9, 21].
Brachial plexus injuries account for 35% of surgical complications in the axillary region and have the most significant long-term morbidity and mortality [10]. In the present case, the medial cord of the brachial plexus and the medial antebrachial cutaneous nerve travelled between the AA and the CT. This atypical relationship of the medial cord with an arterial variation may complicate peripheral nerve blocks or, in general, increase the risk of nerve damage during any procedure within the axilla [12].
The right axillary vein was not anatomically unique in this case, but the course of the venous tributaries may be altered in such arterial variation and can complicate procedures like central venous line placements, arteriovenous fistulas, or impede venous flow and cause swelling [23]. Aside from venous procedures, AA variations such as the one presented in this case may also complicate axillary lymph node dissection, breast augmentation, reconstructive surgery and tumour resections [23].
CONCLUSIONS
While AA variations are common, it is unreported in the literature to see a CT originating from the first segment of the AA. This CT is unique as it provided accessory arteries to the serratus anterior and latissimus dorsi muscles before terminating as the PHCA and SA. The first part of the AA also atypically provided the LTA and TAT. Knowledge of unique arterial variations can impact a wide range of procedures performed by radiologists as well as orthopaedic, vascular, oncology, and plastic surgeons.
Acknowledgments
The authors are very grateful for the donations of these bodies that contribute to the advancement of science and medical education. This study was supported by the Center for Anatomical Science and Education, Saint Louis University School of Medicine.
