Proatlantal arteries, also called proatlantal intersegmental arteries, are carotid-vertebrobasilar anastamosis that persists beyond the embryonic period.

These vessels are frequently associated with anomalies of the ipsilateral vertebral artery, as in this case. In the above case the proatlantal artery is the main supply of the posterior circulation.

Two types of proatlantal artery exist: type I arises from the internal carotid artery and type II arises from the external carotid artery or common carotid artery. The vessels usually obliterate at the 7-12mm embryonic stage.

While proatlantal arteries are normal variants, they are important to identify prior to carotid endarterectomy, as clamping of the proximal carotid artery may lead to posterior circulation infarct.