Congenital external carotid–internal carotid artery anastomosis associated with contralateral non-bifurcating cervical carotid artery

Abstract

Dear Sir, Non-bifurcating cervical carotid artery is a rare anatomical variation of the carotid artery in which the branches of the external carotid artery (ECA) directly arise from the common carotid artery without forming a bifurcation [1, 2]. In addition, cases of congenital EC–internal carotid artery (ICA) anastomosis at the cervical segment forming a large arterial ring have been reported, and it seems to be a variant of the non-bifurcating cervical carotid artery [3]. We wish to bring to your attention a patient showing not only a non-bifurcating cervical carotid artery on one side but also EC–IC anastomosis on the contralateral side. This case suggests that there is a relationship between a nonbifurcating cervical carotid artery and ring formation of the cervical carotid artery. A 71-year-old man underwent CT angiography (CTA) of the extracranial neck vessels, because anomalies of bilateral cervical carotid arteries were discovered at a medical checkup. CTA showed that the right distal common carotid artery changed in caliber at the level of the C6 vertebral body. The major branches of the proximal ECA arose separately from the terminal segment of the common carotid artery or proximal ICA without a proximal main trunk of the ECA (Fig. 1). Thereafter, the artery continued as a normal ICA in the cranial portion. The left carotid bifurcation was located at the level of the C6 vertebral body. The ICA and ECA anastomosed at midcervical level to form a large arterial ring at the proximal cervical segment (Fig. 1). Morimoto et al. [2] first used the term "non-bifurcating cervical carotid artery" as variations/anomalies at the cervical carotid artery in 1990. A non-bifurcating cervical carotid artery is rare, and the overall incidence of the anomaly detected by magnetic resonance angiography was 0.21% [4]. Two hypotheses have been proposed for the development of a non-bifurcating carotid artery [5–7]. The first is agenesis of the common stem of the ECA with regression failure of the hyoid artery. The second is segmental agenesis of the ICA. Embryologically, the cervical carotid arteries develop by complicated processes of regression, and the communication within the vascular network consists of the ventral aorta, dorsal aorta, aortic arches, and intersegmental arteries. The ventral aorta and dorsal aorta communicate via aortic arches. Among them, the first aortic arch (mandibular artery) further regresses, while the second aortic arch (hyoid artery) continues to the stapedial artery. It is generally thought that the ECA develops from both the ventral pharyngeal artery system and the hyoid artery system. According to Lasjaunias et al. [8], the occipital artery (OA) is formed from the proatlantal artery and arises from the primitive ICA, ECA, and vertebral artery at points determined by the sites of regression. In our case, the OAs arose from the right IC and left EC, respectively. When the K. Nakai (*) : T. Kaji : T. Kawauchi :C. Tamura Department of Radiology, National Defense Medical College, 3-2 Namiki, Tokorozawa, Saitama 359-8513, Japan e-mail: nakai@ndmc.ac.jp