AGENESIS OF THE INTERNAL CAROTID-ARTERY WITH A PRIMITIVE TRANSSELLAR COMMUNICATING ARTERY

Agenesis of the internal carotid artery is an unusual developmental anomaly which occurs before the 24 mm stage of embryologic growth. In the majority of reported cases, collateral circulation to the intracranial arteries is from the contralateral internal carotid artery and the vertebrobasilar system via the circle of Willis. We present a case of an unusual collateral pathway in the presence of agenesis of the left internal carotid artery. Three instances of a similar anomalous pathway in the presence of agenesis of the right internal carotid artery have been reported, although none had tomographic studies that demonstrated absence of the ipsilateral bony carotid canal. We believe this to be the first instance of this anomaly reported in the radiologic literature.