Type II proatlantal artery
ICU admission with refractory seizures on background of epilepsy.
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A large vessel (type II proatlantal artery) arises from the left external carotid artery immediately distal to the carotid bifurcation. The left vertebral artery is aplastic and this proatlantal artery enters the foramen magnum. It joins a hypoplastic right vertebral artery to form the basilar artery.
A bovine aortic arch (normal variant) is also noted.
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.
- 1. Luh GY, Dean BL, Tomsick TA, Wallace RC: The persistent fetal carotid-vertebrobasilar anastomoses. AJR Am J Roentgenol.
- 2. Zarghouni M, Marichal D. Persistent bilateral proatlan-tal type II artery. Proc (Bayl Univ Med Cent) 2013; 26 (1): 50-1.