Normal cerebral arterial development and variations

The cerebral vascular architecture is both unique and heterogeneous in its structure, organization, and function. For many years, it was believed that brain vasculature was dominated by nonanastomosing terminal or "end-arteries." This was primarily based upon the observation of discrete distribution of brain infarcts after embolic occlusion of particular vessels. It was not until the detailed anatomy work of Pfeiffer in 1928 that the new concept of an almost-uninterrupted vascular network of brain vasculature was proposed. Since then, the cerebral vascular anatomy and embryology has been studied in great detail. Its full description is beyond the scope of this article, and our aim is to provide a brief overview of the development of cranial arterial anatomy, with special emphasis on commonly encountered anatomical variations that may have clinical implications. The failure to recognize these can lead to misdiagnosis as well as otherwise-preventable iatrogenic injuries and complications. We describe the proposed underlying embryologic processes, pathology and clinical implications of these variations, including aberrant internal carotid arteries, carotid agenesis and hypoplasia, azygous anterior cerebral arteries, arterial fenestrations, and persistent embryonic vessels.