Persistent primitive olfactory artery without a hairpin turn.

Persistent primitive olfactory artery (POA) is a relatively rare variation of the proximal anterior cerebral artery (ACA) that generally follows an extreme anteroinferior course and takes a hairpin turn before continuing to the A2 segment of the ACA. There are other extremely rare variations, such as (1) that continuing to the ethmoidal artery without a hairpin turn, (2) that continuing to both ethmoidal artery and distal ACA with a hairpin turn, and (3) that continuing to the accessory middle cerebral artery with a hairpin turn. We herein report a case of persistent POA without a hairpin turn continuing to the A3 segment of the ACA. We propose calling this new type of persistent POA Type 5.