Absent right common carotid artery associated with aberrant right subclavian artery

Abstract

Rarely, the external and internal carotid arteries arise separately from the brachiocephalic trunk and right subclavian artery (SA) or the aortic arch and reflect the absence of a common carotid artery (CCA). We report a 45-year-old man with absent right CCA associated with aberrant right SA, an extremely rare combination, diagnosed by computed tomography (CT) angiography during follow-up for postoperative aortic dissection. Retrospective careful observation of preoperative postcontrast CT revealed the absent right CCA. Previously reported arch variations associated with absent CCA include cervical aortic arch, double aortic arch, and right aortic arch.

Introduction

The absence of a common carotid artery (CCA) is extremely rare, with only 33 cases reported prior to 2014.¹ In this variation, the right external carotid artery (ECA) arises from the brachiocephalic trunk and the right internal carotid artery (ICA) arises separately from the right subclavian artery (SA). When it occurs on the left, the ECA and ICA arise independently from the aortic arch between the brachiocephalic trunk and the left SA and are thus described as having separate origins.^2,3

An aberrant right SA arising from the aortic arch distal to the origin of the left SA and taking a retroesophageal course is relatively common, having a reported prevalence on computed tomography (CT) angiography among adult patients of 0.47%.⁴ We report an extremely rare case of right absent CCA associated with aberrant right SA.

Case report

A 45-year-old man with sudden-onset abdominal pain, lumbago, and paresthesia of the right lower extremity underwent emergency CT from the chest to abdomen and was subsequently diagnosed with Stanford type A acute aortic dissection. An aberrant right SA was also detected during initial image interpretation. However, extremely low right carotid bifurcation was recognized retrospectively after surgery (Figure 1).

Figure 1.

Postcontrast computed tomography of the upper chest region (a)–(d). There is aortic dissection. The right SA (long arrows) arises from the distal aortic arch and follows a retroesophageal course, indicating it is aberrant. The long dotted arrows indicate the left CCA and the thick arrows, the proximal segment of the right CCA (normally, the brachiocephalic trunk). The short arrow indicates the right external carotid artery and the short dotted arrow, the right internal carotid artery, suggestive of an absent right CCA. SA: subclavian artery; CCA: common carotid artery.

The patient underwent emergency surgery to replace the ascending aorta and total aortic arch and reconstruct three supra-aortic vessels except for the aberrant right SA. The postoperative course was uneventful.

Eighteen months later, follow-up CT angiography from the aortic arch to the intracranial region demonstrated new dissection of the aberrant right SA with formation of a double lumen and extremely low right carotid bifurcation. Because the short common trunk of the right ECA and ICA could be regarded as what would be the brachiocephalic trunk (innominate artery) of a normal individual, we diagnosed the patient with an absent right CCA and not extremely low carotid bifurcation (Figure 2).

Figure 2.

Left anterior oblique (a), anteroposterior (b), and right posterior oblique (c) projections of computed tomography angiography from the aortic arch to the skull base region obtained 18 months after surgery.

The ascending aorta and three supra-aortic arteries were reconstructed. There are double lumina in the aberrant right subclavian artery (long arrow). The long dotted arrow indicates the reconstructed left common carotid artery (CCA); the short arrow, the right external carotid artery; and the short dotted arrow, the right internal carotid artery. Thus, the right carotid bifurcation is extremely low. The extremely short right CCA can be regarded as what would be the brachiocephalic trunk of a normal individual. Therefore, the patient is considered to have an absent right CCA.

Discussion

Rarely, the ECA and ICA arise separately from the brachiocephalic trunk and right SA (right) or aortic arch (left), a variation described as absence of the CCA^1,5–9 or separate origins of the ECA and ICA.^2,3 Berczi and associates¹ uncovered only 33 such cases described in the literature prior to 2014. This variation demonstrates no gender or side preference and has been reported bilaterally in one patient.⁸

Previously reported arch variations associated with absent CCA include cervical,⁵ double, and right¹⁰ aortic arch. Arch variations associated with absence of the CCA may result from simultaneous events during the early embryonic stage. Our patient had an aberrant right SA, but no report associates this variation with absence of the CCA. Rossitti and Raininko⁹ reported a case of absence of the CCA on the left associated with a left persistent trigeminal artery variant, which they speculated was fortuitous.

Six pairs of aortic arches form in the early embryonic stage (Figure 3). The third arches are precursors of the carotid system. The fourth arches develop asymmetrically. The left fourth arch remains continuous with the aortic arch sac and the left dorsal aorta to form the left aortic arch. The right fourth arch, together with part of the right dorsal aorta, forms the brachiocephalic artery and proximal right SA. The dorsal aortae between the third and fourth arches, called the ductus caroticus, regress by the sixth week.^11,12 The ECA forms by migration of the ventral pharyngeal artery from the aortic sac to the third arch.⁷ The CCA normally develops from the root of the ventral aorta between the third and fourth arches. Separate origins of the ECA and ICA occur if the ductus caroticus does not involute and the third arch regresses. Figure 4 illustrates these variations schematically. So, when the CCA is absent, the ECA usually arises proximally to the origin of the ICA. Monaco and colleagues⁷ described the right ECA originating from the brachiocephalic trunk (innominate artery) and the right ICA arising from the SA. Maybody’s group,⁶ however, reported a case in which the right CCA was absent and the ICA arose proximally to the origin of the ECA. The CCA is also absent if the fourth arch involutes and both the third arch and ductus caroticus persist, and the absence is associated with a cervical aortic arch.⁵

Figure 3.

Schematic illustration of six pairs of aortic arches. The first, second, fifth and sixth arches involute. Reproduced with kind permission from Elsevier¹¹.

Figure 4.

Schematic illustration of the double aortic arch model (a) The fourth brachial arch (1) forms the aortic arch (left) and brachiocephalic trunk (right). The third brachial arch (2) forms the carotid sinus and proximal portion of the internal carotid artery. The ductus caroticus (3) is the part of the dorsal aorta between the third and fourth brachial arches. The ventral pharyngeal artery (4) is the primitive external carotid artery that arises directly from the aortic sac. (b) In a normal individual, the bilateral ductus caroticus and right dorsal aorta distal to the right SA (X) involute. (c) In a usual case of absent right common carotid artery (without aberrant right SA), the left ductus caroticus, right third brachial arch, and right dorsal aorta distal to the right SA (X) involute. (d) In the present case, the left ductus caroticus, right third brachial arch, and right dorsal aorta proximal to the right SA (X) involute. SA: subclavian artery.

Our patient had an aberrant right SA. Thus, there was no brachiocephalic trunk. We believe that the short segment of the common trunk of the right ECA and ICA should be regarded as what would be the brachiocephalic trunk (innominate artery) of a normal individual rather than considering it the proximal segment of the right CCA. Therefore, we diagnosed the patient with an absent right CCA rather than extremely low carotid bifurcation. The brachiocephalic trunk usually takes a superoposterior course. The position of the ECA of our patient anterior to the ICA suggested that the ECA arose as the first branch and the ICA as the second branch.

Absence of the CCA is usually asymptomatic and found incidentally. Berczi and associates¹ reported atherosclerotic stenosis of the right ICA in a patient with absent CCA. Our patient had a Stanford A type dissection. Fortunately, the dissection did not extend into the carotid system but into the aberrant right SA. Retrospective examination of emergency postcontrast CT uncovered the extremely low right carotid bifurcation.

Conclusions

We report an extremely rare case of absent right CCA associated with aberrant right SA. The absent right CCA was retrospectively detected by careful observation of postcontrast CT.

Ethical standards

We declare that all human and animal studies have been approved by the Melbourne Health Research Ethics Committee and have therefore been performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments.

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Conflict of interest

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.