Dancing in a Roar: Multilobed Aneurysm Arising From Azygous Anterior Cerebral Artery

Embryologically, anterior cerebral artery (ACA) takes a medial course in 40-day period. Anterior communicating artery develops after 4 days. Along with the development of corpus callosum, ACAs course in a frontal caudal direction [1]. ACA arises from the internal carotid artery distal to the carotid siphon, crosses the anterior perforating substance. It gives off small medial striate vessels and reaches the interhemispheric fissure and connects with the contralateral ACA by the anterior communicating artery. It then turns upward in the direction of the genu of the corpus callosum with which it is intimately associated as it parallels it in a wide arc to continue over the medial surface of the hemisphere [1]. It may occasionally lie in the cingulate sulcus. Right and left ACA vessels run in parallel. Left may possibly course slightly posterior than the right one. It supplies orbitofrontal and medial hemispheric portions of the human brain. The unusual fusion of the paired A2 is either originates from the medial branch of the olfactory artery at the initial 16 mm stage during embryonic development or the continuation of the median artery in the corpus callosum at the 24-mm stage. [2] Among the lower primates, there is no anterior communicating artery. Unpaired ACA is normal in snakes, tortoises, and crocodiles [3]. However, it is a rare variation in human in which A2 segments of both ACAs are represented by a single common vessel. It may have profound clinical implications with an incidence of 1.15 to 5% [1,2,4] which is either due to lack of development or regression of anterior cerebral artery during embryogenesis. Different types of azygos ACA has been described in the literature [4].