In the embryonic period severeal developmental anomalies of the cerebral arteries can occur.
During embryogenesis the brain vascular system continuously adapts the supply of oxygen and other nutrients to the needs of the parenchyma.
These changes often deviate from normal pathway and produce various anatomic variations.
Discussion of cerebral arterial development begins with the formation of the six pairs of primitive brachial arch arteries that either regress or are subject to modifications.
The aortic arches arise from the aortic sac,
course through the branchial arches,
and terminate in ipsilateral dorsal aorta.
Brief overview of the development of cranial arterial anatomy
Fig. 1: Overview of cerebral arteries development. This is only a schematic animation.
ICA-Internal Carotid Artery, MCA-Middle Cerebral Artery, ACA-Anterior Cerebral Artery, AcomA-Anterior Communicating Artery, PCA-Posterior Cerebral Artery, PcomA-Posterior Communicating Artery, LNA-longitudinal neural arteries, BA-Basilar Artery, VA-Vertebral Artery.
References: Beata Feldman, Warsaw / Poland 2013
Internal carotid artery (ICA)
ICA is composed from seven segments.
The first - C1 (cervical) segments derive from the fetal third aortic arches.
Other segments C2–C7 (petrous to communicating) represent cranial extensions of the embryonic dorsal aorta.
Anterior cerebral artery (ACA)
In emryo the last portion of ICA divides into cranial and caudal branches.
Cranial division of the ICA forms the primitive olfactory artery (POA),
and this artery branches off the anterior choroidal artery and middle cerebral artery (MCA).
The POA has two branches,
the one going to the nasal fossa,
and the secondary one - future continuation of the ACA - going more medially.
The latter artery joins with its fellow of the opposite side by the plexiform anastomosis that constitutes the future anterior communicating artery (ACoA).
There is no branch except the POA in the horizontal part of the ACA,
it is postulated that the medial striate artery and the recurrent artery of Heubner derive from the anastomosis between the POA and ACA.
A small embryonic branch known as the median artery of the corpus callosum arises from the ACoA.
This vessel normally involutes.
Middle cerebral artery (MCA)
MCA branches from the primitive ICA proximal to the ACA.
MCA becomes more prominent and gives branches that spread over the cerebral hemisphere.
The MCA development is related to development of the sylvian fissure and insula.
Posterior cerebral artery (PCA)
When cranial and caudal divisions of the ICA are established,
the caudal divisions anastomose with the cranial ends of the longitudinal neural arteries (LNA).
The caudal divisions then regress and become posterior communicating arteries (PComAs).
The caudal divisions also supply the stems of the posterior cerebral arteries.
The PComAs should regress in caliber as the vertebrobasilar system develops.
Presegmental Arteries and Carotid-basilar anastomoses:
Anterior cerebral circulation becomes established as the primitive ICAs reach the developing forebrain.
The paired longitudinal neural arteries (LNA),
precursors of the basilar artery (BA) and partly of vertebral arteries (VAs) form on the medial edges of bilateral vascular networks on the ventral surface of the hindbrain. Small branches arise from the ICA to deliver blood to the LNA while the vertebrobasilar system is under construction.
These branches include three transient presegmental arteries (named after the 5th,
8th,
12th cranial nerves with which they course: trigeminal,
otic and hypoglossal arteries),
one permanent presegemental artery (future PcomA),
and the first intersegmental artery (termed Proatlantic Artery).
These arteries also contribute to the formation of the LNA by anastomosis.
After formation of the posterior communication artery from the caudal branch of the ICA,
the presegmental arteries normally regress,
starting with the otic artery,
followed by the hypoglossal and trigeminal arteries.