![]() The anterior division initially supplies the optic and olfactory regions through primitive arteries. 24 At 4 mm stage (28 days), the ICA branches off into the anterior and the posterior division. Eventually, the ventral pharyngeal artery and the ICA fuse proximally to form the common carotid artery (CCA) and the distal segment of the ventral pharyngeal artery becomes the external carotid artery (ECA). The ventral portion of the 2nd branchial arch disconnects from the dorsal aorta near the origin of the ICA and becomes the ventral pharyngeal artery. ![]() The internal carotid arteries (ICA) appear during the 3 mm embryonic stage (24 days) from the combination of the 3rd branchial arch arteries and the distal segments of the paired dorsal aortae ( Figure 1). Keywords: Circle of willis Embryology Cerebral arteries Arterial variants Stroke Remodeling Learning more about the hemodynamic consequence that these variants may have on the brain territories they supply may help understand better the underlying physiopathology of cerebral arterial remodeling and stroke in patients with these variants. Other common remnants of embryological development include fenestration or duplication (most commonly of the basilar artery), hypoplasia (typically of the posterior communicating artery) or agenesis (typically of the anterior communicating artery). These anastomoses regress when the basilar artery and the vertebral arteries become independent from the internal carotid artery, but their persistence is not uncommon in adults (e.g., persistent trigeminal artery). At this stage, the posterior circulation consists of a primitive mesh of arterial networks that originate from projection of penetrators from the distal carotid artery and more proximally from carotid-vertebrobasilar anastomoses. As the occipital region, brain stem and cerebellum enlarge the internal carotid supply becomes insufficient, triggering the development of the posterior circulation. At day 24 of embryological life, the internal carotid artery is the first artery to form and it provides all the blood required by the primitive brain. Angiogenesis, which occurs mainly by sprouting of parent arteries, is the first stage at which variations can occur. As the arteries supplying blood to the brain develop during embryogenesis, variation in their anatomy may occur and this variation may influence the development of arterial disease. The anatomy of the arterial system supplying blood to the brain can influence the development of arterial disease such as aneurysms, dolichoectasia and atherosclerosis.
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