Teaching Case

Woman, 63 years old. Asymptomatic patient with history of familial hypercholesterolemia, came to our attention after a screening ultrasound examination of the carotid arteries which revealed an unusual finding.

Doppler US examination showed a patent left common carotid artery, with normal wall thickening (0.8 – 1 mm), however, luminal diameter at the level of carotid bifurcation was evaluated nearly 4.5 mm (this value was considered lower than normal, usually between 7 - 10 mm). Doppler US finding was considered suspicious for an inflammatory vasculitis. For this reason the patient underwent a MDCT using angiographic protocol: imaging acquired and multiplanar 3D reconstruction (VR and MIP postprocessing elaboration) revealed separate origins of the left internal and external carotid arteries from the aortic arch and absence of left common carotid artery (Fig. 1, 2). Closed proximal origin of the external carotid artery to the innominate (brachiocephalic) trunk was observed with dorsal origin of the internal carotid artery, emerging about 7 mm behind the first vessel (Fig. 2 a-c). CT angiography did not reveal other associated vascular abnormalities.

The absence of left common carotid artery is a rare congenital anomaly in which the internal and external carotid arteries originate directly from the aortic arch. From 1968 only four cases of agenesis of left common carotid artery have been reported, and no one of these cases underwent a CT examination. Cakirer et al in 2002 reported a similar case evaluated by Magnetic Resonance Angiography. Frequency is equal on the right and the left carotid axis. In about one-half of the cases this anomaly was associated with additional major vascular anomalies. These include double aortic arch, right aortic arch, cervical arch, aberrant right subclavian artery and persistent proatlantal artery.
This malformation is most likely based on atresia of the III or IV branchial artery plus persistence of the ductus caroticus on the involved side.
Agenesis of common carotid artery is usually asymptomatic unless it is associated with a coincidental arterial lesion.
MDCT with Volume Rendering and Multiplanar Reformations shows this unusual finding in a very effective way.