occipital artery arising from the anterior aspect of the internal carotid artery identified by three-dimensional computed tomography angiography

variation of the branches of the external carotid artery (eca) is well known, but it is extremely rare for the occipital artery (oa) to arise from the internal carotid artery (ica). a 87-year-old man was found to have this anatomical variation on the right side by threedimensional computed tomography angiography for vascular mapping of the carotid arteries before superselective intra-arterial catheterization for advanced tongue cancer. imaging showed the oa arose from the anterior aspect of the right ica with the origin located 8.8 mm distal from the carotid bifurcation. the inner diameter of the origin of the oa was 2.1 mm and the angle between the oa and the ica was 62 degrees. it is important to recognize this anatomic variation of the branches of the eca before head and neck microsurgical reconstruction or superselective intra-arterial chemotherapy for oral cancer.