The left vertebral artery (LVA) usually arises from the left subclavian artery medial to the thyrocervical trunk. It then enters the foramen transversarium of C6, passes through the transverse processes of all superior cervical vertebrae, and finally enters the foramen magnum while supplying the brain and spinal cord.
The aortic arch normally gives rise to three vessels: the brachiocephalic trunk (BT), left common carotid artery (LCC), and left subclavian artery (LSA). Variations on this have been observed numerous times and even classified . This report is concerned with the “Adachi TYPE C” variation in which a fourth vessel, an anomalous left vertebral artery, also arises from the aortic arch. The frequency of this variation has generally been reported between 0.68% and 5.8% [2-7]. Two additional studies have reported frequencies of 7.41% and 15.3% [8, 9]. It is also worth noting that these data indicate that angiography, computed tomography (CT) and MRI studies may underreport the prevalence of this anomaly compared with autopsy-based studies.
While performing a cadaveric dissection of the superior mediastinum, an abnormality was noticed at the location of the aortic arch. Upon further examination, it was observed that the aortic arch gave rise to four vessels. The BT, LCC, and LSA were noted to be in their normal locations. A fourth vessel, arising from the aortic arch proximal to the LSA was subsequently found to be the LVA (Figure 1). Further dissection revealed that a branch of the thyrocervical trunk also formed an anastomosis with the aberrant LVA. The LVA itself entered the foramen in the transverse process of C4, while the anastomotic branch may have supplied the cervical vertebrae below C4.
We subsequently explored the aortic arches of the remaining 26 cadavers in the Gross Anatomy course to document other arch variations. In each case, the manubrium was removed, the superior mediastinum was exposed, and the aortic arch and great vessels were dissected. After examination, it was concluded that 4/27 (14.8%) cadavers had an aberrant LVA originating from the aortic arch. No other abnormalities were noted. The three additional instances of this variation did not have the additional anastomosis between the LVA and a branch of the thyrocervical trunk. The four cadavers had lifespans of 87, 81, 89, and 60 years. Three of the four specimens were Caucasian. The cause of death was cardiopulmonary arrest or otherwise unspecified. None of the cadavers exhibiting this anomaly came with any accompanying history of central nervous system symptoms. Interestingly, all four affected cadavers were female. There were 15 female cadavers in total, corresponding to a 26.7% prevalence rate of this aberration in females.
Several aortic arch variations have been previously described including examples where the LCC arises from the BT  and where both vertebral arteries originate as additional branches of the aortic arch . The variation examined in our case report (LVA origination in the aortic arch) has been previously reported [12, 13] at varying frequencies, with most studies reporting a prevalence between 3% and 8% . We found a frequency of 14.8% (n = 27). A previous study recorded five out of six of their anomalous cadavers as female . Combined with our findings, this suggests that this anomaly is more prevalent in females.
The development of this variation may involve several factors. Blood vessels develop with the association of growth factors such as vascular endothelial growth factor-A164/165 and placenta growth factor . The latter especially induces the formation of large, stable blood vessels. Release of these factors may be increased, decreased, or temporally varied to allow the LVA to arise from the aortic arch rather than the LSA.
Embryologically, cervical intersegmental arteries appear longitudinally from the aortic arch as the heart and aorta move caudally. The seventh cervical intersegmental artery gives rise to the LSA, while the dorsal division gives rise to the LVA . The sixth cervical intersegmental artery usually disappears, but in this case it may have remained, allowing blood flow directly from the aortic arch . Because of reduced blood flow through the typical origination of the LVA (i.e., the dorsal division of the seventh cervical intersegmental artery), origination of the LVA from the aortic arch was then possible. Additionally, there was an observed anastomosis between a branch of the thyrocervical trunk and the aberrant LVA in the primary case in this report. This may have occurred due to a portion of the blood flow persisting through the dorsal division of seventh cervical intersegmental artery.
It seems as if this variation may be more common than described in the literature. Our findings support studies reporting higher prevalence rates [8, 9] and female predominance. Perhaps the discrepant prevalence rates and the serendipitous nature of these discoveries call for more systematic examination of the aortic arch of each cadaver dissected in laboratories. The aberrant left vertebral is unlikely to have any effect on blood flow, but its presence may well complicate aortic arch surgical and endovascular procedures. Disconnection or compromise of the aberrant vessel could also have cerebral consequences. If the incidence is indeed as high as we suspect, the anomalous vertebral artery is at higher risk in surgical procedures requiring isolation of arch vessels or access to the aortic arch itself. At that point, disruption of cerebral blood flow could be significant.