Anomalous Origin of the Right Vertebral Artery from the Right Common Carotid Artery Was Uncovered during an Allcock’s Test

Anomalous origin of the right vertebral artery from the right common carotid artery was uncovered during an Allcock’s test.

An 80-year-old woman underwent stent-assisted coil embolization for a right internal carotid artery-posterior communicating artery aneurysm 1 year ago. The patient underwent follow-up DSA. We attempted to insert a 4 French (Fr) sheath inserted into the right brachial artery and led a 4 Fr catheter into the right vertebral artery (RVA). Subsequently, we searched for the root of the RVA in the subclavian artery without success. As the contrast agent was injected, RVA was not depicted while the root of the internal thoracic artery and thyrocervical trunk were depicted (Fig. 1). The tip of the catheter was guided to the brachiocephalic artery. As the contrast agent was injected with left anterior oblique view at 10 degrees, the right common carotid artery (RCCA), subclavian artery, and RVA was visualized. While inserting the catheter into the RVA was challenging, we successfully managed to do so by pulling up the catheter from the brachiocephalic artery by applying torque. Subsequently, the right neck was compressed, and an Allcock’s test was attempted. However, the contrast agent stopped at the cervical portion and did not reach the intracranial region (Fig. 2). There was no backflow of blood through the 4 Fr catheter. Angiography of the brachiocephalic artery revealed that the RVA originated from the RCCA (Fig. 3). It ascended close to the carotid artery while meandering (Fig. 4). It is likely that as we compressed the right carotid artery, the RVA was also compressed, and the contrast agent stagnated in the cervical portion of the RVA. As the compression weakened, the contrast agent flowed from the RVA to the intracranial part, and Allcock’s test was performed (Fig. 5).

Fig. 1 DSA of the right subclavian artery. The vertebral artery was not visible, but the origin of the internal thoracic artery and thyrocervical trunk were visible.

Fig. 2 Lateral view of the right side of the neck in the digital angiography. The patient’s neck was compressed, and contrast agent injected from the right vertebral artery stagnated.

Fig. 3 Front view of the angiography of the brachiocephalic artery. (A) Left is with subtraction while right is without subtraction. (B) Right vertebral artery originated from right common carotid artery.

Fig. 4 Lateral view of the brachiocephalic artery. (A) Left is with subtraction while right is without subtraction. (B) Right vertebral artery originated from right common carotid artery and ascended close behind the carotid artery.

Fig. 5 Lateral view of the Allcock’s test. Contrast agent from the right vertebral artery flowed into the intracranial section by weaking the pressure of the compression and Allcock’s test could be performed. The aneurysm achieved complete occlusion.

A vertebral artery (VA) usually enters the transverse foramen (TF) of the sixth cervical spine and ascends behind the carotid artery while passing through the TF. However, in this patient, 3-dimensional CT angiography (3DCTA) revealed that the RVA originated from the posterior wall of the RCCA, entered the TF of the fourth cervical vertebra, and ascended close to the carotid artery (Fig. 6). In this case, pressure was applied on the neck at the level of the fourth cervical vertebra. Therefore, the portion of RVA not surrounded by bone was compressed right behind the internal carotid artery along with it.

Fig. 6 Three-dimensional CT angiography. The cervical portion with bone is visualized on the left side in an anteroposterior view. The RVA can be seen entering the TF of the fourth cervical vertebra. (A) The left vertebral artery also enters the TF of the fourth cervical spine. (B) The right side demonstrates the portion without bone in a posteroanterior view. The RVA originates from the posterior wall of the right common carotid artery. The arrow indicates the RVA. RVA, right vertebral artery; TF, transverse foramen

In the 3DCTA, the presence of an aberrant right subclavian artery (ARSCA) was not observed; however, a left vertebral artery (LVA) arising from the aorta was identified (Fig. 7). The LVA also entered the TF of the fourth cervical spine.

Fig. 7 Three-dimensional CT angiography revealing the aorta from behind. Aberrant right subclavian artery is not observed. A left vertebral artery arising from the aorta is seen.

Iwashita et al. reported that RVA from RCCA is rare. Previously reported cases of the RVA originating from the RCCA almost all showed its association with an ARSCA.¹⁾ Maiti et al. reported anatomic variation in the aortic arch and its branch. Their study included the RVA originating from the RCCA merging the ARSCA, the LVA originating from the aorta, the absence of the brachiocephalic artery, and so forth.²⁾ Uchino et al. evaluated the prevalence of variations in both VA origin and its level of entry into TF. In total, 2287 patients by CT angiographic images were considered. There were 3 cases of RVA originating from RCCA (0.13%).³⁾ Maiti et al. indicated the possibility that the incidence of anomalous origin of a VA is underestimated. DSA is the gold standard; however, other modalities such as 3DCTA, MRI, and ultrasonography can play a role in diagnosing VA pathology.²⁾ Most available papers regarding the RVA originating from RCCA are case reports from international studies. Of the 41 aggregated cases from 33 case reports, 12 cases were without ARSCA. Among the 12 cases, there were 7 cases of merged LVA originating from the aorta, 2 cases of right-sided aortic arch, and 4 cases of an absence of the brachiocephalic artery. Three cases did not show merging with any other anomaly. Therefore, most cases of RVA originating from RCCA merged other anomalies. Variations in the VA origin and level of entry into TF are strongly related.³⁾ The level of entry into TF is known for 12 among the 41 cases mentioned before. Therefore, we aggregated these 12 cases for which the level of entry was known. In 3 cases, the VA entered into TF at the third cervical vertebra; in 6 cases, at the fourth cervical vertebra; and in 3 cases at the fifth cervical vertebra. This anomaly is usually clinically asymptomatic and found incidentally during angiographic examinations.⁴⁾ Our case is rare in terms of not merging ARSCA; meanwhile, it is common in terms of merging another anomaly such as the LVA originating from the aorta. Ishikawa et al. reported a case similar to ours.⁴⁾

Embryologically, the 7 cervical intersegmental arteries arise from the dorsal aorta. The VA is formed bilaterally by the longitudinal anastomoses of the cervical intersegmental arteries. These anastomoses formed the distal portion of the VA. The seventh cervical intersegmental artery is attached to the subclavian artery and forms the proximal part of the VA.¹⁾ Anomalies can occur if the first-sixth intersegmental arteries do not regress. If the first or second intersegmental artery persists, the VA arises from the internal or external carotid artery, that is, the proatlantal artery I or II. If the third-sixth intersegmental arteries persist, the VA originates from the common carotid artery or the aorta.⁵⁾ In our patient, the fifth intersegmental artery persisted, which entered the TF of the fourth cervical vertebra, resulting in the observed anomaly. The schematic illustration is presented in Fig. 8. RVA originating from the RCCA is a rare anomaly. Here, the observed phenomenon depended on the vessel course of the VA, the cervical spine where the RVA entered the TF, and the position of the catheter. When an RVA is not depicted in the angiography of subclavian artery or during manual compression of the neck, this anomaly may exist. In the instance of this anomaly, the RVA tends to enter the TF of the third, fourth, or fifth cervical vertebra. Therefore, attention must be paid to the precise location of pressure application during Allcock’s test and the positioning of the catheter.

Fig. 8 A schematic illustration. (A) On the left is a normal case, where the longitudinal anastomoses from the first to seventh intersegmental artery occur, the seventh intersegmental artery develops into a part of the subclavian artery, the dorsal branch of the first to sixth intersegmental artery disappears and the vertebral artery VA develops. (B) On the right is our case, where the longitudinal anastomoses from the first to fifth intersegmental artery occur, part of the right fifth intersegmental artery persists, and the RVA develops. Therefore, the RVA originates from the right common carotid artery and enters the transverse foramen of the fourth cervical spine. CCA, common carotid artery; ECA, external carotid artery; ICA, internal carotid artery; RVA, right vertebral artery; SCA, subclavian artery; VA, vertebral artery

Acknowledgments

We would like to thank Honyaku Center Inc. for English language editing.

Disclosure Statement

The authors declare that there are no conflicts of interest related to this work.

References

• 1)  Iwashita H, Ogata A, Koguchi M, et al. Anomalous origin of the right vertebral artery from the right common carotid artery. J Neuroendovasc Ther 2021; 15: 475–477.
• 2)  Maiti TK, Konar SK, Bir S, et al. Anomalous origin of the right vertebral artery: incidence and significance. World Neurosurg 2016; 89: 601–610.
• 3)  Uchino A, Saito N, Takahashi M, et al. Variations in the origin of the vertebral artery and its level of entry into the transverse foramen diagnosed by CT angiography. Neuroradiology 2013; 55: 585–594.
• 4)  Ishikawa K, Yamanouchi T, Mamiya T, et al. Independent anomalous origin of the right vertebral artery from the right common carotid artery. J Vasc Interv Neurol 2018; 10: 25–27.
• 5)  Ota T. Letter to the editor regarding “Anomalous origin of the right vertebral artery from the right common carotid artery”. J Neuroendovasc Ther 2022; 16: 283–285.