File:Cerebral blood supply development 01.jpg

Embryonic stage

• 4-5 mm - hindbrain (i.e., future posterior fossa) is supplied by two parallel neural arteries (or channels). These arteries obtain their blood supply from carotid-vertebrobasilar anastomoses given by the trigeminal artery (TA), the otic artery (OA), hypoglossal artery (HA), and the proatlantal artery (ProA)
• 5-8 mm - basilar artery (BA) forms from the consolidation of the neural arteries.
• 7-12 mm - vertebral arteries (VA) forms from transverse anastomoses between cervical intersegmental arteries, beginning with the ProA and proceeding downward to the 6th intersegmental artery,
• 11-12 mm - (35 days) development of the MCA is first identified as small buds originating proximal to the ACA on the anterior division of the primitive ICA.
• 16-18 mm - MCA becomes more prominent, the plexi fuse into a single artery and further branches pierce the cerebral hemisphere.
• 18 mm - stem of the ACA gives rise to the olfactory artery.
• 21-24 mm - formation of the anterior communicating artery (ACOMM).

• A - In early phases of development the posterior circulation relies almost entirely from blood supply coming from the anterior circulation through carotid-vertebrobasilar anastomoses.
• B and C - As the posterior fossa structures and the occipital lobe grow, the posterior circulation becomes progressively independent from the anterior circulation with obliteration of the anterior-posterior anastomoses from caudal to rostral maintaining in the majority of adult only one connection between the distal basilar arteries with the carotid artery via the posterior communicating artery.