Clinical History
An arterial phase MDCT study of the thorax was performed on a 10 year old girl with symptoms of dysphagia looking for an extrinsic vascular ring or other cause of oesophageal compression. Previous medical history included repair of a tracheo-oesophageal fistula complicated by tight oesophageal stricture formation, requiring multiple dilatations.
Imaging Findings
There was no vascular ring but evaluation of the vascular anatomy revealed an unusual variant (Fig. 1). The first branch of the aortic arch was large and trifurcated to give rise to both external carotid arteries and the right brachiocephalic trunk. The brachiocephalic trunk then divided into the right internal carotid artery and subclavian artery; the right vertebral artery arose as normal from the right subclavian artery. The second branch of the aorta gave rise to the left internal carotid artery. The third and final branch gave rise to the left subclavian artery from which the left vertebral artery arose as normal.
A clue to the abnormal branching pattern is seen on the axial images with separate internal, external and vertebral arteries all visible on upper mediastinal slices (Fig. 2). This “six vessel” sign is analogous to the “four vessel” sign seen with a double aortic arch.
Discussion
Aortic branching patterns can show significant variation with joint origin of the right brachiocepahic trunk and left common carotid (so called bovine arch) being the most common1. Unilateral absence of a carotid artery is well described but there are only two cases in the literature of bilateral absent common carotid arteries, neither in the era of CT2.
Branching anomalies are usually asymptomatic in childhood and detected incidentally on imaging for other reasons. However, stenoses of the vessels can develop later in life and with the increasing use of endovascular techniques it is important to be aware of the possibility and range of variant anatomy3.
Differential Diagnosis List
Absence of both common carotid arteries
Congenital vascular anomaly
Acquired arterial occlusion
Final Diagnosis
Absence of both common carotid arteries
