Congenital Unilateral Absence of the Internal Carotid Artery Associated with Aneurysms of Different Arteries: A Review

There are 466 cases of absent unilateral (398) and bilateral (68) internal carotid artery (ICA) published in online books, abstracts, and original articles from 2020 to 2021. Of the 398 cases of absent unilateral ICA, 95 were associated with aneurysms. The analysis of these cases includes age, nationality and gender, location of aneurysm(s), description, and scheme of carotid-vertebrobasilar angioarchitecture mode in the brain base, as well as hypothesis on the embryonic background of accompanying vascular variations and abnormalities. The calculated ratio between the number of absent unilateral ICA cases and the number of absent bilateral ICA cases is 5.8:1. The ratio between the total number of cases of absent unilateral ICA and those associated with aneurysms is 4.2:1. The association between the posterior communicating middle cerebral anastomosis and intercavernous (trans-sellar or intercarotid) channel with the absence of both anterior cerebral and anterior communicating arteries is common. More than half of the cases with aneurysms are located at the anterior segment vessels of the cerebral arterial circle. This review is based on the description and explanation of embryology and morphology of absent unilateral ICA with aneurysms, which would be a significant contribution to published literature on this topic, especially due to the fact that nothing similar has been published since 1957.