Circle of Willis is anatomical formationvessels, localized on the basis of the brain, which provides a redistribution of blood between different vascular basins in the presence of insufficient blood supply to the brain. It is a closed polygon, which is a vascular anastomosis.
Willis circle formed from the front and backthe connective arteries (PSA and ZSA), the initial segments of the anterior and posterior cerebral arteries (PMA and ZMA), the wedge-shaped segment of the internal carotid artery (ICA) and the distal main artery (OA).
In its front section is carriedcollateral circulation between the carotid arteries (for example, VSA and right PMA - PSA - VSA and left PMA), and in the back section - between the carotid artery system and the vertebrobasilar system (VSA - AAS - ZMA - OA).
It is worth noting that normally developed andA fully closed circle of Willis is found in only half of the world's population. Hypoplasia or aplasia of PCA and PMA, as well as PSA and CSA hypoplasia, are common. In the anterior section, deviations from the norm are detected a little less frequently than anomalies in the structure of the posterior section.
ПСА весьма вариабельна в своем строении, размерах and location: options are possible from complete absence to the formation of a wide fistula at the point of contact of the PMA, it is also possible to double or triple PSA. The anterior trifurcation of the anterior cerebral artery occurs very rarely: both ASDs start from the same ICA. In this case, the circle of Willis is open in the front section. A rather rare anomaly is the presence of an additional PMA, called Wilder's artery.
The back section is normally found only approximately athalf the population of the planet. Anomalies of the posterior part can be very diverse: a large variation in size, asymmetry of the discharge of the branches of the arteries, the absence of segments or even arteries. The most common anomaly is the difference in the diameters of the vertebral arteries: hypoplasia of one with simultaneous hypertrophy of the other. At the present stage, it is believed that one vertebral artery dominates, and the second is recessive in terms of their overall contribution to the blood flow in the vertebrobasilar basin. Permissible asymmetry 50%. ASA in diameter is usually slightly less than PSA. Hypoplasia of the ASA is also quite common.
Option development circle of Willis - pronouncedan anomaly of the structure of the intracranial vertebrobasilar system: there is no complete integration of the vertebral arteries of both sides into the main artery, anastomoses of irregular structure are possible, or arteries go in isolation. In the case of aplasia of the main artery or ASD, the posterior section of the arterial circle of the brain is formed. It is from the back that the perforating branches go, going to the middle and intermediate brain. It turns out that an open willysian circle can be both in the anterior segment and in the posterior segment. Moreover, it can be completely open (the connecting arteries are absent) and incompletely (with hypoplasia or narrowing).
Changes in the normal structure of the arterialCircle of the brain can be both congenital and acquired - the result of adaptation of certain parts of it to the changing conditions of hemodynamics in various pathologies of the great vessels of the head, which often develop in these cases. Evaluation of individual features in the structure of the vascular bed is carried out according to angiography and is very important in neurological practice. It is necessary to distinguish when making a diagnosis of changes in the arteries: which are the cause and which develop as a result of pathological changes.
