Infraoptic anterior cerebral artery or carotid–anterior cerebral artery anastomosis: A very rare embryological variation. Case series and review of literature

Purpose: An infraoptic course of the anterior cerebral artery (ACA) is a rare cerebrovascular variation that can be associated with anterior communicating artery aneurysm. The purpose of this study is: 1. Describe infraoptic ACA or Carotid-ACA anastomosis. 2. Discuss the embryology. 3. Demonstrate this rare variation on CT/MR angiography. 4. Discuss its clinical significance. 5. Understand the anatomy for appropriate management of associated vascular pathology (Anterior communicating aneurysm). 6. Literature review. Methods: We describe 2 cases with CT/MR angiographic findings of this rare vascular variation along with review of embryology and literature. Results and conclusion: Generally, ACA arises from the internal carotid artery (ICA) terminus and runs medially superior to the optic nerves and communicates with contralateral ACA through the anterior communicating artery. An infraoptic course of the A1 segment of the ACA is associated with a low ICA bifurcation, usually located intradurally at or just above the level of the origin of the ophthalmic artery. Rarely, infraoptic origins of A1 are proximal or at the level of origin of the ophthalmic arteries and arise below the optic strut possibly extradurally. Abberant ACA course has been shown to be associated with aneurysms which needs prompt recognition, to allow optimum treatment planning (surgical/endovascular). Our first case has bilateral infraoptic ACA seen on CT angiography. The second case has ipsilateral (right) infraoptic ACA with associated anterior communicating artery aneurysm.