Central nervous system disorders

V./1.3.: Posterior or vertebrobasilar cerebral circulation

V./1.3.1.: Vertebral arteries

According to its name, the posterior circulatory system delivers blood to the caudal structures of the brain. It is supplied by the vertebral arteries, which pass through the foramen magnum and enter the posterior cranial fossa. They ascend on the sides of the medulla oblongata in the lateral medullary cistern and than at the border of the medulla and the pons in the front of the bulbopontine sulcus merge to form the single basilar artery (vertebrobasilar junctio, VBJ). The vertebral arteries are often of different caliber on the two sides with the left being larger (~40%). Depending on the vascular territory of this system, the brainstem, the cerebellum and parts of the occipital cortex, the it’s circulatory disorders can lead to different vascular syndromes.

V./1.3.2.: Main arteries and their supplied regions of the vertebral arteries (posterior cerebral circulation)

V./1.3.2.1.: Anterior spinal artery

The artery originates with a small branch from the vertebral artery, it unites with its fellow of the opposite side, than as a single trunk descends in the front of the ventral surface of the spine in the (anterior) ventral median fissure.

V./1.3.2.2.: Posterior spinal arteries

They are smaller branches than the beformentioned arteries, usually originate from the posterior inferior cerebellar artery.

V./1.3.2.3.: Posterior inferior cerebellar artery (PICA)

Ordinarily it is a branch of the vertebral artery, also it may originate from the basilar artery. It winds backward, curves around the medulla oblongata to extend toward the cerebellar tonsils, while provides blood supply to the medulla oblongata, inferior olive. Than it divides into two terminal, the medial and the posterolateral branches. The first branch supplies the lower portion of the vermis till the level of the fastigium and the posterolateral branch irrigates the cerebellar tonsils as well as ipsilateral cerebellar hemispheres (“tonsillohemispheric branch”). Both artery anastomose with the upper celebellar arteries. In case of absent or hypoplastic variation of the PICA, these arteries take over.

V./1.3.2.4.: Basilar artery (BA) 

The basilar artery extends from the vertebrobasilar junction to the basilar bifurcation (basilar apex) in the medial pontine cistern, where it bifurcates to form the right and left posterior cerebral arteries. It usually ascends straight upward in the basilar sulcus on the ventral surface of the pons, but during aging it develops a curving course and often deflects to one side. The undermentioned branches supply the brain, brainstem and cerebellum as well as the inner ear, the diencephalon and the basal ganglia.

V./1.3.2.4.1.: The pontine rami

They are a number of small vessels which supply the anterior (median and paramedian branches) and lateral (short and long circumferential branches) portions of the pons.

V./1.3.2.4.2.: Anterior inferior cerebellar artery (AICA) 

This artery ordinarily arises from the caudal two-thirds of the basilar artery, but rarely may originate from the vertebral artery with a common trunk or independently of the PICA. It passes the medial pontine cistern, than runs in the lateral pontin cistern(cerebellopontine angle) toward the cerebellum, where it divides into medial and lateral branches supplying the cerebellum and anstomose with the other two arteries of the cerebellum. The labyrinthine artery distributing to the internal ear can emerge as a branch of the basilar artery (~15 %), however generally it originates from the anterior inferior cerebellar artery, where it forms a loop and variably enters the internal acoustic meatus.

V./1.3.2.4.3.: Superior cerebellar artery (SCA).

SCA originates from the basilar artery just few millimeters below its bifurcation in the upper part of the medial pontine cistern. Than it enters the ambient cistern and curving around the mesencephalon and pons it courses backward the cistern of tectal lamina (quadrigeminal cistern, cistern of Galen, cistern of the great cerebral vein). The segment running adjacent to the brainstem has a close spatial relation to the trochlear nerve, the basal vein (Rosenthal), the cerebral peduncle and the trigeminal nerve. Besides irrigating the neighboring structures of the brainstem (mesencephalon and the upper part of the pons), it supplies the cerebellar hemispheres, the upper portion of the vermis, the middle and superior cerebellar peduncles and the dentate nucleus.

V./1.3.2.4.4.: Posterior cerebral artery (PCA)

It is the terminal branch of the basilar artery. It arises parallel to the beformentioned artery with the oculomotor nerve emerging between them. In the clinical practice the segment extending from the basilar artery to the origin of the posterior communicating artery is called the P1 segment. The following (P2) segment curves around the midbrain and the ambient cistern and it reaches the superior cistern (quadrigeminal cistern or Galen's cistern or cistern of the great cerebral vein)  where it terminates. In practice P3 and P4 segments are usually also mentioned, they are divided into

• - cortical,

• - central (also known as thalamoperforating) and

• - choroidal branches.

• 1) Out of the cortical branches the calcarine artery supplying the visual cortex, the occipitotemporal artery supplying the base of the temporal and occipital lobe, the inferior temporal arteries supplying the uncus, the hippocampal formation and the inferiomedial part of the temporal lobe and the parietooccipital artery supplying the medial surface of the occipital and parietal lobe should be mentioned. The posterior pericallosal artery is originates from the parietooccipital artery it wraps around and supplies the corpus callosum, the precuneus, the paracentral lobule. In case of an absent posterior pericallosal artery it’s vascular territory is served by the pericallosal artery. All of the cortical branches form several anastomotic connections with the branches of the anterior and middle cerebral artery.

• 2) The posterior thalamic perforating arteries arise from the top of the basilar artery or more commonly from the commencement (P1 segment) of the posterior cerebral artery. They have branches reaching the substancia nigra and supplying the red nucleus, the posterior portion of the hypothalamus and the medial and paraventricular nuclei of the thalamus.

• 3) The choroid plexus of the third and lateral ventricles is supplied by two clinically significant arteries, the medial  and lateral posterior choroidal arteries. The medial posterior choroidal artery courses backward in the interpeduncular and ambient cistern and posteriorly enters the top of the third ventricle, while it gives off branches to the lateral geniculatre body and the pulvinar. The lateral posterior choroidal artery originates proximal to the medial artery and through the choroidal fissure, paralell to the anterior choroidal artery it enters the inferior horn of the lateral ventricle, where it anastomoses with the beformentioned artery.