Aberrant origin of right vertebral artery from the arch of aorta

Abstract

We present a rare case of an aberrant right vertebral artery originating from the arch of aorta distal to the origin of the left subclavian artery. The incidence of this particular variant of aberrant origin of the right vertebral artery is extremely uncommon with only seventeen cases reported in literature to date. This case was incidentally detected on a staging positron emission tomography-computerized tomography (PET-CT) scan for lung cancer. We review the incidence, embryological mechanism, and clinical importance of this aberrant course of the right vertebral artery.

A 62-year-old male patient underwent staging whole-body 18F-flurodeoxyglucose (18F-FDG) positron emission tomography (PET) scan, coupled with contrast-enhanced computerized tomography (CT) scan for lung cancer. The scan showed a metabolically active soft tissue mass lesion in the lower lobe of the right lung and few metabolically active mediastinal lymph nodes. The scan showed the left-sided aortic arch. The first branch of the aortic arch was the brachiocephalic artery, which subsequently divided into the right common carotid artery and right subclavian artery. It was followed by origin of the left common carotid artery and then origin of the left subclavian artery. In addition, it was noticed that the right vertebral artery (VA) was originating as the last direct branch of the arch of aorta, distal to the origin of the left subclavian artery. The pre-vertebral segment of the right VA passed superiorly and to the right, crossing the midline with a retro-esophageal and retro-tracheal course (Fig. 1). The left VA was normal in course.

Fig. 1.

a Axial contrast-enhanced CT scan shows origin of the right vertebral artery directly from the arch of aorta (red circle). It was the last branch of the arch distal to the origin of the left subclavian artery. b Prevertebral course of the right vertebral artery (arrow) passed superiorly and to the right, crossing the midline with a retro-esophageal and retro-tracheal course. c 3D-reconstructed image shows direct origin of the right vertebral artery as the fourth branch of arch of aorta (arrow)

Discussion

Typically, the VAs are the first branches of bilateral subclavian arteries. Anomalous origin of the VA is uncommon [1]. The most common anomaly is the origin of the left VA from the arch of aorta, between the origin of the left common carotid artery and the left subclavian artery. Anomalous origin of the right VA is less common and is divided into three categories: (1) direct origin from the arch of the aorta, (2) origin from the carotid arteries (or from the brachiocephalic artery), and (3) duplication of the artery.

Only 17 cases of an anomalous origin of the right VA as the last branch from the arch of aorta have been reported in the literature till 2018 [2]. In these cases, the right VA originated distal to the origin of the left subclavian arteries. The other reported locations of anomalous origins from the aortic arch were between the right common carotid artery and the right subclavian artery, directly from the brachiocephalic artery and on the left side between the left common carotid artery and left VA [1]. Association of the anomalous right vertebral artery with other congenital variants like the diverticulum of Kommerell or bovine aortic arch is extremely uncommon [2, 3].

The embryological right dorsal aorta normally disappears. The left dorsal aorta forms the distal part of the aortic arch. The remaining part of the aortic arch and its branches develop from the residual parts of six sets of matched aortic arches on both sides of the midline, after its selective regression. The proximal right fourth arch persists as a part of the right subclavian artery and distal part regresses. The left fourth arch regresses, except a small part which forms the segment of aortic arch between the common carotid artery and subclavian artery on the left side. The proximal seven intersegmental arteries (ISAs) in cervical region are linked together with longitudinal anastomoses on both sides. The ISAs eventually regress except for the seventh ISA. The seventh cervical ISA forms part of the subclavian artery and origin of the VAs [4]. The distal part of the VA develops from the longitudinal anastomoses. Aberrant anastomosis at any time during the embryonic development of the arch results in anomalous origin of the VAs. The final anatomy of the arch and the origin of its branches depend on the time and location of this anastomosis. The variation in the present case is explained by the normal development of the longitudinal anastomosis of the cervical ISA, persistence of the right dorsal aorta, and the obliteration of the right 4th aortic arch [5] (Fig. 2).

Fig. 2.

Schematic representation of the embryological mechanisms of underlying anatomical variants of the vertebral artery origin. a Normal anatomy. RVA and LVA arise from ipsilateral subclavian arteries, which are derived from seventh intersegmental arteries. b Aortic origin of the RVA. Persistence of the proximal right dorsal aorta which links the RVA to the thoracic aorta distal to the left subclavian artery. RVA right vertebral artery, LVA left vertebral artery

Aberrant origin of the right VA is usually asymptomatic, as also in our patient. Clinical symptoms like headache, dizziness, and dysphagia can be attributed to the aberrant course of the anomalous artery. Altered hemodynamics of abnormal course of vessels may predispose to increased risk of dissection or aneurysms [6]. Moreover, it is important to know this variant of anatomy to avoid inadvertent iatrogenic injury, and resultant catastrophic ischemic event of the brainstem, during catheter angiography or cardiothoracic surgery [7].

In conclusion, we present an extremely rare case of anomalous origin of the right vertebral artery directly from the arch of aorta, distal to the origin of the left subclavian artery. The aim of this report is to increase the awareness of this aberrant anatomy and potential clinical implications.

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Conflict of interest

The authors declare that they have no conflict of interest.

Ethical approval

Ethical approval was obtained from institutional review board.

Informed consent

Informed consent was obtained from the patient.