Circle of Willis: anatomy, development options, pathology

The circle of Willis in the cerebral vascular system was described more than three hundred years ago by the English physician T. Willis. The structure of this arterial ring is of great importance in unfavorable conditions, when certain parts of the nervous tissue experience insufficient arterial blood flow due to blockage or stenosis of the arteries. Normally, even with abnormally developed vessels of this circle, a person does not feel the existing features due to the full functioning of other arteries.

The norm of the structure of the Circle of Willis is defined, but not everyone can boast of it. According to some data, the classic arterial ring is developed in only half of people, other researchers put the figure at only 25% of people, and all the rest have certain anomalies in the branching of blood vessels. This, however, does not mean that those whose arterial circle is developed in a peculiar way will have any negative symptoms or disorders, but nevertheless, manifestations of impaired blood flow can periodically make themselves felt by migraines, vascular encephalopathy, or even manifest as acute disorders of cerebral circulation.

There are a lot of options for the development of the Circle of Willis. This may be tripling (trifurcation), aplasia, hypoplasia, or the complete absence of any arterial elements. Depending on the type of artery branching, its clinical significance and prognosis are determined.

To determine the anatomy of the circle of Willis, non-invasive and invasive diagnostic procedures are used; they are carried out according to indications for specific patient complaints. In other situations, anomalies are discovered by chance during an examination for another pathology.

Circle of Willis - what is it?

Almost 300 years of anatomical research, plus the capabilities gained with the development of modern instrumental research - Dopplerography, ultrasound and several types of angiography, have made it possible to establish that the circle of Willis in half or most cases does not correspond to the medical norm. However, recently it has not been customary to talk about an absolute norm, because each person’s body may have individual structural features.

This applies to any operating system, including arterial blood flow. Not everyone has the so-called classic arterial ring. And this means. that in many people the peculiar development of the anastomotic ring can lead to various disorders or negative sensations.

Nature has provided for the possibility of interrupting cerebral circulation in an adult. Since the brain is a vital organ, its blood supply should not be interrupted. For this purpose, arteries are located at the base of the brain (more precisely, in its subarachnoid space, between the soft membrane of the brain and the spinal cord).

Signs of abnormal structure

Clinical signs of underdeveloped VC occur only when the body has developed a serious pathology in the bloodstream system, which has led to insufficient blood flow to the brain cells:

Atherosclerotic plaques have formed on the arteries;
Thrombosis of arteries of various diameters;
Entry into the artery of an embolus, which the blood flow transported from the left-sided ventricle, or the left-sided atrium;
Coronary insufficiency, which leads to impaired blood flow;
Pulmonary artery insufficiency also disrupts blood flow, and the brain does not receive the required amount of nutrients;
Aneurysm of the cerebral arteries.

Symptoms of impaired blood flow due to anomalies of the circle of Willis

The symptoms of impaired blood circulation correspond to the cause of the pathology in the bloodstream system, as well as in the organs of the brain. With a developing stroke, the symptoms are characteristic of this pathology; with encephalopathy, there will be completely different symptoms.

Generalized symptoms of impaired blood supply to the brain:

Severe dizziness;
Severe pain in the head, which intensifies when changing the position of the head;
Inability to think correctly - difficulties in the intellect;
Reduced concentration on objects and situations;
A sharp decrease in memory;
Inattention;
Cardiopalmus;
Dyspnea;
Panic attack;
Photophobia:
Irritability;
Drowsiness;
Fatigue of the body;
Deviations in the visual organ - blurriness and blurriness of objects;
Clogged eyeball, doubling of objects;
Tinnitus, which sometimes intensifies when the auditory nerve reacts to increased sounds;
Constant feeling of fatigue.

What functions is it responsible for?

The main purpose of the vascular formation is to constantly supply the brain with blood. It should occur in a wide variety of functional damage and failures caused by serious diseases, arterial occlusions or damage. This is a kind of circuit of fuses, which provides for the possibility of blood flow through the arteries, which are normally responsible for other functions.

The responsibilities of the departments included in the Circle of Willis include:

provide the brain with the necessary nutrition in case of damage or congenital anomalies of the arteries;
support the functionality of the brain during spasms or abnormal vascular locations;
prevent damage to nerve tissue if the activity of the cervical arteries is impaired;
avoid the development of areas of oxygen starvation by redirecting blood to such an area.

Fact! Only a system that is formed without violations copes with its purpose normally. And half, sometimes ¾ of all people have deviations from the physiological structure. The presence of such anomalies is associated with intrauterine development, which humanity has not yet learned to control.

Prevention

Prevention of this organ is based on the prevention of all possible pathologies of the body’s blood flow system with an anomaly of the circle of Willis, and the measures are as follows:

Constant monitoring of the coagulation system;
Monitoring the blood cholesterol index in case of VC anomaly;
Normalize the blood pressure index;
Proper nutrition for anomalies of the ring of Willis;
Treatment of all pathologies of the cardiac organ and vascular system;
Timely cure of vegetative-vascular dystonia due to anomaly of the circle of Willis;
Engage in hardening of the vascular system from childhood;
Avoid stressful situations that can trigger spasms.

Possible pathologies

In medicine, deviations in the structure are diplomatically called variant anatomy of the circle of Willis. There are many of them, and not every person has only one, sometimes there are several at once. The most common of them is trifurcation. It is found in that part of the internal carotid artery, which is called the suprasphenoid, it can be posterior (when 3 cerebral arteries begin from this fragment) and anterior - both anterior cerebral arteries begin from the carotid. Aplasia (absence due to congenital malformations) of the posterior communicating artery is often noted. This option can be with both PCA, and with all connecting arteries, and even with the main artery.

Variant anatomy of the arteries of the base of the brain

There are many types of structure of the Circle of Willis. They depend on how the process of vessel formation occurred in the prenatal period, and it is impossible to predict this process.

Among the most common anomalies of the cerebral arteries are: aplasia, hypoplasia of individual branches, trifurcation, fusion of two arteries into one trunk and some other varieties. Some people have a combination of different vascular anomalies.

The most common variant of the development of the circle of Willis is considered to be posterior trifurcation of the ICA, which accounts for almost a fifth of all anomalies of the arterial ring. With this type of structure, three cerebral arteries immediately begin from the ICA - anterior, middle and posterior, and the PCA will be a continuation of the posterior communicating branch.

A similar structure is typical for the circulatory system of the fetal brain at 16 weeks of pregnancy, but later the sizes of the vessels change, the posterior connective branch decreases, and the remaining branches increase significantly. If such a transformation of the vessels does not occur, then the child is subsequently born with posterior trifurcation.

Another common variant of the structure of the circle of Willis is considered to be aplasia of the PCA, which occurs under various unfavorable external conditions and genetic abnormalities during embryogenesis. In the absence of this artery, the circle of Willis does not close on the side where it is not present, that is, there is no relationship between the internal carotid artery system and the basilar area.

The absence of PSA is also diagnosed, but much less frequently than the posterior one. With this type of structure of the arterial ring, there is no relationship between the branches of the carotid arteries, so it is impossible, if necessary, to “transfer” blood from the vessels of the left half to the right.

Aplasia of the anterior communicating artery does not provide a chance for blood flow to the affected part of the brain by delivering blood from the opposite vasculature, since the carotid arteries are disconnected. When the PCA is not formed, there is no relationship between the anterior and posterior parts of the circle of Willis, and the anastomoses do not function. This type of branching of the arterial system seems unfavorable in terms of possible decompensation of blood flow disorders.

Rare forms of the circle of Willis structure include:

Median artery of the corpus callosum;
The union of the anterior cerebral arteries into one common trunk or their parietal course, when they are in close contact with each other;
Anterior trifurcation of the internal carotid artery (two anterior cerebral arteries arise from one carotid artery);
Split, double anterior communicating artery;
Bilateral absence of PCA;
Trifurcation of the carotid arteries on both sides.

Non-classical types of the circle of Willis are more typical for its anterior part, but since defects of the posterior part are of greater clinical significance due to a worse prognosis, they are diagnosed more often. The conclusions of experts indicate that the vast majority of patients with impaired blood flow in the brain have certain anomalies of the circle of Willis, and this indicates its enormous importance in supplying the brain with blood in pathology.

Anomalies in the branching of blood vessels and the openness of the circle of Willis make it unable to perform the role of an anastomosis in critical situations - during a hypertensive crisis, thrombus formation, spasm, atherosclerosis. In addition, some types of branching involve large areas of necrosis of nervous tissue due to circulatory failure. For example, anterior trifurcation means that most parts of the hemisphere receive blood from the branches of just one artery, so if it is damaged, the scale of necrosis or hemorrhage will be significant.

When the arteries of the base of the brain are classically developed, all the necessary connecting branches are present between them and the caliber of each vessel is within normal values, they say that the Circle of Willis is closed. This is the norm, indicating that the anastomosis is stable, and in case of pathology, the blood flow will be compensated to the maximum.

fully open VC

An open circle of Willis is considered a serious anomaly that predisposes to various types of cerebrovascular accidents. There is an openness of the anterior part of the arterial ring, which occurs with aplasia of the PSA or anterior trifurcation of the carotid artery, and an openness of the circle of Willis due to anomalies of the posterior part of the vascular bed - aplasia of the posterior communicating, basilar artery, posterior trifurcation of the ICA.

If the connecting branches are completely absent, they speak of a complete openness of the circle of Willis, and when the arteries are preserved, but stenotic, hypoplastic, then the openness is considered incomplete.

If the circle of Willis is open – good or bad

If the circle of Willis is open, this is a developmental anomaly that causes a negative impact on the fetus. For some reason, there is a deviation from the scenario provided by nature, and the formation of the choroid plexus leads to asymmetry of the VC.

The question of what to do with such deviations arises with the development of diseases, and before that (sometimes until very old age), no one even suspects that he has it at all. Aplasia, hypoplasia or trifurcation are detected during studies using special diagnostic methods. The need for it is revealed against the background of the development of diseases, but sometimes a negative scenario develops suddenly.

Interesting! The development of negative states is typical in old age, when the compensatory ability inherent in an open circle weakens. When it fails to normalize arterial blood flow, complications or diseases occur.

Diagnostics

Most people have anomalies of the circle of Willis, and this abnormality is detected only by examining the cerebral vessels.

If there are pronounced symptoms of the development of an arterial aneurysm, then the following diagnostic check of the condition of the cerebral arteries is performed:

A non-invasive technique for examining an organ is computed tomography angiography (CT). This is an x-ray technique in which a special contrast agent is injected into the bloodstream of the brain to identify the affected areas of all branches of the cerebral vessels in case of an anomaly of the circle of Willis;
The non-invasive MRI (magnetic resonance imaging) technique for an anomaly of the ring of Willis is the most universal method for a comprehensive study and for obtaining an image of the entire vascular system in detail;
Invasive organ testing - angiography . This technique is based on catheterization of the arterial system of the head, during which a contrast agent is introduced into the arterial system. And an X-ray of the vascular system is performed.

Circle of Willis on a diagnostic image

Consequences

Anomalies in the development of VC never lead to positive processes. This is a failure in the functional purpose of an organ or system, which up to a certain time nature is able to compensate. Asking whether this is good or bad usually begins when the disease develops, and modern medicine has not yet learned to treat abnormalities in the structure of blood vessels.

She only treats diseases that become their consequences. The most common of these are aneurysm and ischemic stroke. There is no open-circle treatment, and only if consequences appear—rupture of a vascular aneurysm and subarachnoid hemorrhage, or ischemic stroke—does there arise a need for surgical (aneurysm ligation) or conservative treatment, as with any subarachnoid hemorrhage.

Structure and functions of the arterial circle of the brain

Reduced blood circulation in the brain is a life-threatening phenomenon. Human anatomy is such that the function of compensating for insufficient blood flow is performed by the arterial ring (circle of Willis) located in the subarachnoid space at the base of the brain.

The vessels of the brain are connected to each other (anastomosed) on the basis of the GM. The following vessels form the pool of the circle of Willis:

Anterior cerebral artery: initial segment (a. cerebri anterior).
Anterior communicating artery (a. communicans anterior).
Internal carotid artery: supracuneiform segment (a. carotis interna).
Posterior communicating artery (a. communicans posterior).
Posterior cerebral artery: initial segment (a. cerebri posterior).

In his work, Willisius Thomas describes the anastomosis in the form of a heptagon - the heptagon of Willisius. But after conducting research, M. A. Tikhomirov discovered that the shape of the ring is nine-sided. The connection between the vessels of the brain is centralized in the circle of Willis.

Impaired blood flow in the cervical vessels can lead to insufficient blood circulation to the brain. To prevent a situation of decreased blood flow, a “backup option” is provided - a compensatory arterial circle. This is its function. The carotid arteries, connecting with each other, anastomose with the vertebrates. It is thanks to this connection that, in the event of cerebral vascular obstruction, blood circulation is not disrupted and all tissues receive a sufficient amount of substances.