Incidence of the occipital artery arising from the internal carotid artery identified by three-dimensional computed tomographic angiography.

Variants of the branches of the external carotid artery are common, but it is extremely rare that the occipital artery arises from the internal carotid artery. We investigated the incidence using three-dimensional computed tomographic (CT) angiography. In 265 patients with cancer of the head and neck, we did CT angiography for vascular mapping of the external carotid artery and its branches before reconstruction or superselective intra-arterial chemotherapy. The origin of the occipital artery was detected in 514 of 530 carotid arteries (97%); the incidence of it arising from the internal carotid artery was 0.2%.