The circle of Willis: what is it, options for development, pathology

Named in honor of the researcher who discovered it, the circle of Willis is a vivid illustration of the concept of "anastomosis".

This is the name given to the system of messages-anastasies, which looks like short bridges, between a number of blood vessels, in this case, arteries that form a closed ring (circle) at the base brain.

Since we are talking about a communication system that feeds the whole brain with glucose and oxygen, there is no need to talk about the importance of the existence of this vascular formation - it is obvious.

The variety of variants of the circle of Willis is created by the presence of various ways of connecting these main arterial blood supply lines.

General information about the basal circulation, its vascular structure and its functions

The circle of Willis is the very beginning of the entire circulatory network, which rises from the base of the brain upwards as along its surface, and in the depths, in order to further, endlessly branching, reach each individual cell in its tissues and structures.

The arterial system closed in a ring allows it to carry out its main function (uninterrupted supply of blood to the brain) as impossible more successfully, because when power outages from one vessel appear, an automatic switch to blood supply from another.

And power outages may occur due to the appearance in one of the arterial branches:

• spasm;
• narrowing of the lumen of another etiology (due to the formation of cholesterol deposits, thrombus, wall thickening from scar formation, due to compression from the outside);
• aneurysmal deformity of the lumen;
• atrophy or desolation (decline with overgrowth of the lumen - obliteration).

Or it may be a consequence of hypoplasia (congenital underdevelopment), which manifested itself at a critical moment.

About the structure of this part of the circulatory system

There are many options for constructing the arterial ring of the base of the brain, but arteries are its mandatory components:

• anterior cerebral (its initial fragment);
• posterior cerebral (at its initial segment);
• connecting (front and rear);
• internal carotid (supra-wedge-shaped fragment).

The main vascular lines are 2 carotid and 2 vertebral arteries (one on each side of the body). Sleepy ones enter the cranial cavity through the carotid canal passing in the pyramid of the temporal bone and opening at its apex, vertebrates - passing the large occipital foramen.

The blood supply is created by intermediate "bridges" that have individual characteristics: they may be completely absent, be in a state of aplasia, hypoplasia, or be tripled (the presence of three elements instead of two, or the phenomenon trifurcation).

In the classically symmetric version, the vertebral arteries, merging, form one powerful basilar (main), which runs along the pons of varoli and gives branches for nutrition of the cerebellum and oblong brain. Anteriorly, it is divided into 2 posterior connectives (right and left), at the same level creating also 2 posterior cerebral ones.

At the level of its confluence with the internal carotid, the central cerebral arteries (left and right) branch off from both sides of the anastomosis in the distal direction. The branches of both internal carotids close in front, forming a semicircle, from which 2 parallel anterior cerebral arteries extend forward. The single anterior connecting bridge connecting them from behind is part of the arc formed by the fusion of the branches of the internal carotid arteries.

Development and formation options

The opinions of scientists about the frequency of occurrence of the classic variant are very different from each other: according to some data it is 50%, according to others - 25, according to the third - even less. Depending on the method of vascular branching, determined by the peculiarities of intrauterine development, both the presence and the degree of development of some segments of the system will differ from the canonical one.

Possible options for the absence are cases when there are no arteries:

• basilar;
• all connecting;
• connecting front;
• connecting rear (one or both);
• connecting the front and one of the connecting rear.

Cases of anterior or posterior trifurcation can also be represented by variations in arterial discharge:

• the posterior cerebral from the internal carotid (a separate option - with the simultaneous absence of the anterior connective);
• both anterior cerebral from one of the internal carotid.

Existence is also possible:

• hypoplasia of one of the posterior cerebral;
• incomplete doubling of the anterior cerebral branch.

The most common occurrence is the presence of posterior trifurcation of the internal carotid line (with the beginning from it three cerebral arteries at once: posterior, anterior and middle), while the posterior cerebral arteries move away from the posterior connecting. Such an anomaly, having arisen in a 16-week-old fetus, may persist or undergo a gradual transformation into a fully vicious circle.

The situation with aplasia of the posterior connecting branch, when there is communication between the arteries of the basilar and internal carotid only on one side, and on the other, the circle does not closed.

With the less often diagnosed absence of the anterior connecting jumper, there is no communication between the carotid arteries, fraught with the impossibility of pumping blood from one side to the other.

With aplasia of the anterior communicating branch, dissociation occurs between the carotid arteries, and with the lack of formation of the posterior connecting posterior and anterior segments of the circle of Willis practically not connected together.

More rare findings during the study include cases:

• the presence of the median trunk of the corpus callosum;
• fusion into one trunk of both anterior cerebral arteries or their parietal contact with each other;
• anterior trifurcation (with the departure of both anterior cerebral from the same carotid);
• the presence of bilateral trifurcation of the carotid highways;
• absence of both posterior communicating branches;
• the presence of a doubled anterior connecting artery.

Pathological structure of the arterial basilar circle

Vessels of the anterior half (carotid and anterior cerebral) are distinguished by the greatest developmental stability, while the anatomy of the posterior cerebral and connecting vessels is characterized by a great variability of branching.

However, deviations in the structure of the anterior half are of much greater importance due to the significant severity of clinical symptoms and the greater severity of the prognosis. In addition to the ideal (closed), there are options for the open basilar circle:

• fully;
• not completely.

In the first case (in the absence of connecting branches), the communication between the anterior and posterior parts is completely absent, in the second (with their intactness, but being in a state of stenosis or hypoplasia) speak of incomplete openness of the basilar circle, which allows it to function not to full power.

Signs of structural anomalies

Anomalies in the structure of blood vessels may not manifest themselves for years, until reaching an age when changes become stable, and the level of cerebral circulation becomes unstable, but may appear already in youth.

The most constant is the appearance of:

• headaches;
• dizziness;
• decrease in attention, memory (in severe cases - intellectual capabilities).

Due to the presence of cerebral ischemia with the involvement of fine brain structures, deviations of both neurological and mental plan appear - from emotional instability to neuroses and panic attacks.

The most characteristic symptom of the circle of Willis pathology is migraine attacks. The most susceptible to it are those with an open circle or anomalies in the development of the posterior half of the system:

• posterior trifurcation;
• hypo- or aplasia of the posterior communicating branches.

Due to ischemia of the areas of the brain responsible for vision, the onset of an attack is preceded by the appearance of a visual aura (bright zigzags, flashes and sparks in the eyes).

Other symptoms of insufficient blood supply are signs of DEP (discirculatory encephalopathy) with disorder both in the emotional-volitional and in the purely physical sphere - from unreasonable weakness to a decrease work capacity.

The peak of the disorder of functions with an abnormal structure of the basal circle is the development of a stroke with the development of paralysis and paresis, sensory and motor disorders, in severe cases - with the onset of a coma.

The emergence and development of an aneurysm can also not manifest itself for decades and is often an accidental finding in the study of cerebral vessels.

About the causes of pathologies

Deviations in the development of the structures of the circle of Willis occur, as a rule, during intrauterine development, the course of which can be caused by abuse by the pregnant mother:

• smoking her;
• her use of alcohol or drugs;
• overdose of hypnotics and sedatives;
• unauthorized use of drugs not prescribed by a doctor.

The course of pregnancy can be affected by chronic or acute stress of high intensity, viral infection and the like.

The cessation of the functioning of the existing and developed system of messages of the base of the brain can be caused both by the same chronic household intoxication, and changes in the properties of blood (due to its high coagulability), as well as diseases that cause degeneration of the vascular wall or narrowing (closing) of the lumen vessels:

• atherosclerosis;
• thrombosis;
• fatty or air embolism when large arteries are injured by sharp edges of bones in their fracture, or other acute and chronic reasons.

Diagnosis of anomalies

In the recognition of arterial pathology of the base of the brain, visual (neurological and ophthalmological) examination is insufficient.

Therefore, they resort to instrumental research of blood vessels by methods:

• ultrasound dopplerography;
• MRI (magnetic resonance imaging);
• radiopaque angiography;
• transcranial doppler sonography;
• magnetic resonance angiography;
• selective angiography.

About dysfunction treatment

It is prescribed and carried out in the presence of documented pathology, accompanied by patient complaints and the presence of a clinical picture of a particular syndrome.

Depending on the prevalence of manifestations, conservative treatment is performed with:

• general vascular (antispasmodics, sedatives);
• tranquilizers;
• antidepressants;
• anti-inflammatory and analgesic (Ibuprofen and Ketorol categories).

Cases of migraine deserve separate study and differentiation from similar conditions, after which an adequate diagnosis of therapy is prescribed.

In case of ineffectiveness of drug treatment or the onset of acute pathology, microsurgical treatment is used using the following techniques:

• stenting;
• clipping;
• balloon angioplasty.

On the prevention of conditions caused by pathology of the circle of Willis

It consists in observing the recommendations of the pregnant woman on the assortment, dosage, frequency of taking medications, using only drugs prescribed by the doctor. It is necessary to protect yourself as much as possible from being hit by a viral infection, to avoid stressful situations in every possible way (family members and colleagues of the pregnant woman are also called to this).

The prevention of life-threatening acute vascular conditions should lead to the maintenance of the most active lifestyle in order to prevention of problems with blood vessels, and when they appear, it is necessary to actively cooperate with the attending physician with the unconditional execution of his prescriptions.