Anomalous external carotid-internal carotid artery anastomosis diagnosed by computed tomography angiography: a case report

An anomalous anastomosis between the external and internal carotid arteries forming an arterial ring at the level of the cervical internal carotid artery is an extremely rare variant, and its embryological origin remains unclear. This report describes a rare arterial variation at the level of carotid bifurcation incidentally discovered in a 67-year-old man. Computed tomography angiography revealed an anomalous anastomosis between the external and internal carotid arteries at the level of the C2–3 intervertebral space with a small proximal cervical segment of the internal carotid artery and the occipital artery originating at this anomalous anastomosis. This report may be of embryological significance and contribute to understanding the mechanisms of carotid artery formation.