The dominance of dorsal scapular artery as the blood supply to muscles of the back in the absence of two primary vessels: a cadaveric case report

Embryologically, the SA develops from the dorsal aspect of the aorta during the seventh week of development. Similarly, the ITA, ACA, TCA, and SSA are joined together during development to form the TCT [1]. While the right SA develops from the fourth aortic arch, right dorsal aorta, and right seventh intersegmental artery, the left SA arises from the left seventh intersegmental artery [19].

The TCT, arising from the SA, typically gives rise to four branches: ITA, ACA, SSA, and TCA; however, variations of these branches do exist [1]. Ostrowski et al. demonstrated that the most common branches of the TCT are the ITA, SSA, and TCA with a prevalence of 89.02% (73/82 sides of necks on CTA) and reported that the ACA branching from the TCT was rare with a prevalence of 1.22% (1/82 sides of necks on CTA) [4]. Additionally, Lippert and Pabst described that branches from the TCT, such as the ITA, SSA, and TCA may arise independently in about 5% of cases [3]. In our case, the TCT on the right side of the body gave rise to only the ITA and ACA. Zangpo et al. described a similar case using CTA where only the ITA and ACA arose from the TCT [7]. Similarly, Takafuji et al. demonstrated that a TCT with only an ACA and ITA was present in 11.1% of cases (16/144 dissected subclavian arteries) [5].

The SSA, after branching from the TCT travels inferior and lateral across the anterior scalene muscle, and SA, continuing posteriorly to the clavicle and scapula to reach the supraspinous and infraspinous fossa where it provides blood supply to the supraspinatus and infraspinatus muscles, and skin and joints around the shoulder [1, 2, 8, 10]. Variations of the SSA’s origin have been previously described in literature as the third part of the SA [10], axillary artery [11], subscapular artery [8], and the dorsal scapular artery [9]. Weiglein et al. dissected 498 sides of the neck and found the SSA to originate from the TCT (27%), SA (12%), internal thoracic artery (11%), or from trunks such as the cervico-scapular trunk (22%), dorso-scapular trunk (4%), and the cervico-dorsoscapular trunk (also known as the TCA, 24%) [6]. Pyrgakis et al. showed that the SSA originated from the third part of the SA in 1.6% (1/62 sides of the neck) of cadaveric specimens studied [10]. Takafuji et al. demonstrated that the SSA branched independently from the SA in 26% of cases (37/144 sides of the neck) and in 2.8% of cases (4/144 sides of the neck) it was completely absent [5]. In our case, the SSA did not arise from the TCT, SA, axillary artery, subscapular artery, or the DSA. The complete absence of SSA is a rare and important finding in our study.

The TCA, also known as, the transverse colli artery, is typically a branch of the TCT and travels superiorly to the SSA through the posterior triangle of the neck transversely bypassing the inferior belly of the omohyoid muscle towards the anterior portion of the trapezius muscle where it provides its blood supply [1, 2, 15, 20]. Studies previously published have demonstrated that the TCA is consistently present in 100% of cadaveric specimens and originates from the TCT [20, 21]. However, variations of the TCA exist. Takafjui et al. found that the TCA branched from the TCT in 93 out of 144 dissected sides of the neck (64.6%) [5]. In the same study, the TCA was shown to branch from the second part of the SA in 4.9% of cases and the third part of the SA in 8.3% of cases [5]. Takafjui et al. further demonstrated that the TCA was absent in 15.3% of cases (22/144 sides of the neck) and in another 22 cases the TCA branched independently from the TCT and SA (15.3%) [5]. Another study by Kumar et al. reported a bilateral absence of TCA on a single cadaveric specimen [12]. In our case, the TCA was absent on the right side of the neck from the TCT and from the SA completely without any independent branches from these vessels providing blood supply to the trapezius muscle.

The DSA has been reported to have variations in its origin [13, 14]. Lai et al. described the DSA originating from the TCA in 38 out of 79 neck dissections (48%), the second part of the subclavian artery (22%), the third part of the subclavian artery (25%), and in 5% of cases arising from the axillary artery [13]. In a cadaveric study, Verenna et al. reported that in 71% of the cases (112/158 sides of the neck), the DSA originates from the SA and in 35% (55/158) the DSA originates from the TCT [14]. In our case, the DSA originated from the third part of the SA and provided two branches that were the sole source of blood supply to the trapezius muscle, in addition to its normal blood supply to levator scapular and rhomboid muscles. Published literature shows that SSA can originate from the DSA [9], however, in our case, the SSA was completely absent. When dissecting the branch from the DSA to the supraspinatus muscle, it was evident that the vessel was not the SSA since it did not follow the typical course posteriorly to the clavicle and the supraspinous fossa [2]. A limitation of this case report was the inability to dissect the infraspinous fossa to confirm if the branch of the DSA supplying the supraspinatus muscle anastomosed with circumflex scapular artery. Literature of the DSA as the only source of blood supply for the trapezius muscles and branches to the supraspinatus muscle in a single study has not been previously reported in the literature, to the best of our knowledge.

This case report presents anatomical anomalies that are clinically significant in reconstructive procedures of the head, neck, shoulder, chest and upper back. The TCA and SSA may be used in reconstructive arterial flaps for cervicomental scars and defects of the head and neck following surgical oncology procedures. The supraclavicular flap, a fasciocutaneous flap from the skin of the shoulder and supraclavicular region, most commonly uses the TCA (93%) and SSA (7%) as primary vessels for the procedure [16]. The use of the TCA as an arterial flap can be spread to cover larger areas such as the anterior chest and clavicle [15]. Muppireddy et al. described how the TCA is a safe vessel for arterial flaps because it can anastomose and is an easily dissectible artery due to its location [18]. Additionally, patients who undergo targeted radiation therapy or treatment for recurrent tumors of the head and neck are at increased risk of damage to the vessels of the neck, specifically the external carotid artery and its branches, therefore, utilization of the TCA is a safe option for reconstructive surgery [20]. The DSA is also a clinically significant vessel used in dorsal scapular artery perforator flaps. This type of reconstructive procedure spares the use of the trapezius muscle as a flap, decreasing post-surgical complications such as donor site morbidity and loss of range of motion of the muscle [17].