Aberrant course of the right petrous internal carotid artery (ICA) associated with right type 1 proatlantal artery and bilateral occipital arteries arising from the ICA diagnosed by computed tomography angiography

To describe a case of multiple extremely rare cervical arterial variations.

A 55-year-old man with a tentative diagnosis of right internal carotid artery (ICA) stenosis was examined using computed tomography (CT) angiography for the evaluation of vascular lesions in the neck and head region. A 64-slice CT machine was used.

On CT angiography, there was laterally located and narrowed petrous segment of the right ICA, indicative of aberrant course of the petrous ICA. Right vertebral artery (VA) was small in caliber and a relatively large anomalous artery arose from the proximal right ICA. This anomalous artery entered the posterior fossa via the foramen magnum, indicative of a type 1 proatlantal artery. Right occipital artery (OA) arose from the proximal ICA. The left OA also arose from the proximal ICA.

An aberrant course of the petrous ICA is an extremely rare arterial variation which is formed by segmental agenesis of the cervical ICA, and the collateral channel passes through the middle ear cavity. It can be dangerous during middle ear surgery. The type 1 proatlantal artery is also an extremely rare arterial variation formed by the persistence of the proatlantal intersegmental artery. It is clinically significant because of its unique blood flow from the carotid system to the vertebrobasilar system. The OA rarely arises from the proximal ICA. Identification of these cervical arterial variations before surgery and vascular intervention are important to avoid complications during the procedure.