The structure of the vessels of the brain. Collateral circulation of the brain. Arteries that feed the brain

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Large branches enter the system of arteries of the head, neck and face. They depart from the convex surfaces of the arteries that make up the aortic arch: the innominate (brachiocephalic trunk), and to the left - from the common carotid and subclavian.

Arteries of the head and neck - large vessels extending from the aortic arch and carrying blood to the organs of the neck, head and face.

Artery anatomy

At the level of the cartilage of the II rib on the right, the brachiocephalic trunk departs from the aorta after the trachea and up to the brachiocephalic vein on the right. It moves to the right and upward and is divided at the sternoclavicular joint on the right into 2 arteries: the right common carotid and subclavian.

Branches of the aortic arch: 1 - aortic arch; 2 - brachiocephalic trunk; 3 - left common carotid artery; 4 - left subclavian artery.

The right cervical artery is shorter than the left common carotid artery by 20-25 mm. The common artery is located behind the muscles: sternocleidomastoid, hyoid-scapular and muscles that cover the middle fascia of the neck. It moves up vertically to the transverse processes of the vertebrae of the neck, without dividing into branches. Above the thyroid cartilage, both carotid arteries (right and left) are divided into internal and external with almost the same diameter.

The large subclavian artery consists of the right one, which departs from the brachiocephalic trunk, and the left, which departs from the aortic arch. The length of the left subclavian artery is 2-2.5 cm longer than the right one.

Important. The artery under the clavicle is responsible for the blood supply to the brain from the back of the head, cerebellum, spinal cord in the cervical part, muscles and organs of the neck (partially), shoulder girdle and upper limb.

Arteries of the neck, head and face

Photo 2 shows the dislocation of the arteries of the head and neck:

1. Superficial temporal and its branches.
2. Deep temporal.
3. Maxillary.
4. Back ear.
5. Occipital.
6. Orbital.
7. Average meningeal.
8. lower alveolar.
9. External sleepy.
10. Facial.
11. Lingual.
12. Internal sleep.
13. Superior thyroid.
14. General sleep.

Arteries of the brain

1. Anterior artery of the brain.
2. Middle artery of the brain.
3. Sleepy interior.
4. Posterior communicating artery.
5. Posterior cerebral.
6. Cerebellar superior.
7. Main.
8. Cerebellar anterior inferior.
9. Vertebrate.
10. Cerebellar posterior inferior.

Functions of the arteries

The arteries of the head, neck and face transport blood, nutrients: trace elements, vitamins and oxygen to controlled areas. Let's consider in more detail.

common carotid artery

The paired artery extended into the sternocleidomastoid muscle, scapular-hyoid, trachea, esophagus, pharynx and larynx. The endings of the artery are located in the carotid triangle, next to the thyroid cartilage of the larynx, where the branches are divided into external and internal - the terminal carotid arteries.

External carotid artery

Stretched along the carotid and submandibular triangle, submandibular fossa (inside the parotid gland). Consists of anterior, posterior, medial and terminal groups of branches. It ends with two terminal branches near the neck of the lower jaw.

Anterior branch group

1. Thyroid anterior superior artery divided into the sublingual branch and the laryngeal superior. Responsible for blood supply to the hyoid muscle and thyroid gland. Anastomosis (connection or fistula of vessels) with the thyroid lower artery.
2. The lingual artery consists of branches:

• suprahyoid, supplying blood to the bone under the tongue, suprahyoid muscles;
• sublingual, supplying blood to the gland under the tongue, the mucous membrane of the bottom of the mouth, gums, the jaw muscle under the tongue;
• dorsal branch and deep artery of the tongue, supplying the tongue.

Anastomosis with the mental artery.

1. The facial artery is divided into:

• palatine ascending - supplies blood to the pharynx and palatine tonsil;
• tonsil branches - blood flows to the tonsil of the palate and the root of the tongue;
• chin - supplies blood to: the floor of the mouth, the digastric and maxillo-hyoid muscles, the gland under the tongue;
• upper labial - upper lip;
• lower labial - lower lip;
• angular (terminal branch) - external nose and medial corner of the eye.

Anastomosis occurs between: ascending palatine and descending palatine, ascending pharyngeal arteries; submental and subhyoid; angular and dorsal nasal (from the ophthalmic) artery.

Back branch group

1. The occipital artery supplies blood to the sternocleidomastoid and muscles of the cervical spine, the back of the head, including the skin under the hair, auricle.
2. The auricular artery gives a branch - the posterior tympanic artery and supplies blood to the occipital skin and muscles, the auricle, the mastoid process with its cells, and the tympanic cavity. Connects (anastomosis) with the occipital artery and superficial temporal.

Blood supply to the tissues of the face

The function of blood supply to the soft tissues of the face is performed by the branches of the arteries:

• ophthalmic (frontal, eyelid, dorsal, nasal and supraorbital arteries);
• external carotid (lingual, facial, submental, sublingual);
• temporal superficial (transverse facial, zygomatic-orbital);
• maxillary (infraorbital and chin).

The orbit is supplied with arteries: the ophthalmic ( branch) and middle meningeal (branch of the maxillary artery) through the lacrimal artery of the anastomotic branch.

The oral cavity is fed from the branch of the lingual, which belongs to the external carotid artery. The hyoid branch refers to the lingual artery belonging to the external carotid. The cheeks and lips are supplied with blood by the facial artery. The floor of the mouth and the area under the chin are fed by the submental artery (from the facial branch). The bottom of the oral cavity is supplied with blood from the maxillo-hyoid branch (from the inferior alveolar artery). The mucous membrane of the gums is supplied with blood by the alveolar artery with dental branches. The cheeks are supplied with blood by the buccal, as a branch of the artery of the upper jaw.

Blood flows to the maxillary gums from the anterior superior alveolar arteries. To the palate, tonsils and gums, blood comes from the descending palatine artery - a branch of the maxillary artery. The blood supply of the tongue is carried out by the arteries: lingual (outer carotid branch) and facial (almond branch).

The salivary glands are supplied with blood by arteries:

• gland under the tongue - sublingual and submental;
• parotid gland - branches of the temporal superficial, transverse facial;
• gland under the lower jaw - the facial artery.

The nasal cavity is fed by the arteries: anterior ethmoidal, posterior ethmoid (branches of the ophthalmic artery), posterior lateral nasal (branches of the palatine sphenoid artery), posterior artery of the nasal septum (branches of the palatine sphenoid artery).

The maxillary teeth are fed with blood from the arteries: the posterior and anterior upper alveolar. The mandibular teeth are supplied with blood from the inferior alveolar artery.

Diseases of the blood arteries

Among the diseases of the arteries of the head, neck, face, the following are considered dangerous:

1. Cerebral aneurysm: cerebral, intracranial.

They are characterized by protrusion of the walls of the arteries and the absence of their three-layer structure. With the rupture of a cerebral aneurysm, subarachnoid hemorrhage is possible with the penetration of blood into the region of the subarachnoid space of the brain.

Aneurysms are arteriovenous and arterial, and often occur at the site of branching of the arteries. The shape is: saccular aneurysm (for example, anterior communicating artery, bifurcation of the middle cerebral artery), internal fusiform and fusiform.

1. Atherosclerosis.

Narrowing of the cervical arteries and the brain or atherosclerosis are accompanied by frequent bouts of unbearable headache, from which memory is reduced. The vessels narrow when cholesterol plaques are deposited and accumulated on the walls, reducing the lumen. The speed of blood flow decreases, so the vessels pass less blood, and with it nutrition and oxygen.

Important. Atherosclerotic plaques form in the cracks in the walls of arteries in their pathological conditions. They lose their elasticity with an increase in blood cholesterol levels, which leads to the appearance of cracks.

Plaques attract platelets, which contribute to blood clotting and the formation of blood clots. With acute vasoconstriction, a stroke can occur, speech is impaired, and vision is reduced. Perhaps a pre-infarction state, cerebral infarction or hemorrhage, if blood circulation is sharply disturbed.

1. Hypoplasia.

Hypoplasia (often congenital) of the vertebral artery disrupts hemodynamics (blood circulation), especially in the posterior regions of the brain. This leads to dysfunctions of the heart and circulatory system, internal organs and vestibular apparatus. For diagnosing and checking the artery, studying its functional state, roundabout blood flow, angiography is performed - a contrast x-ray study. At the same time, they will find out how long the pathological process has lasted.

With a weakening of blood flow in two, right or left vertebral arteries, the blood circulation of the central nervous system worsens. These arteries supply 30-32% of blood to the brain. With osteochondrosis, blood flow decreases and a posterior cervical sympathetic syndrome occurs, similar in symptoms to migraine. For diagnosis, Doppler ultrasound, neck x-ray, MRI are performed.

If cervical artery syndrome is confirmed, treatment is aimed at eliminating dizziness, blackouts, headache, auditory and visual disturbances, and arterial hypertension.

1. Rhesus conflict

Important. The velocity of the middle cerebral artery is measured for a comparative assessment of the fetal blood flow velocity, if pregnant women have Rh immunization, have given birth to children with Rh (-) and Rh (+) blood affiliation, the fetus or newborn has a different degree of hemolytic disease.

With the help of ultrasound and dopplerometry of blood flow in the middle cerebral artery of the fetus, one can easily diagnose the severity of HDP in Rh-conflict, fetal diseases that affect hemodynamics, including anemic syndrome, to study the fetal circulation in dynamics, without using invasive technologies.

The brain regulates all the structures of the body, allowing you to maintain a stable functioning of physiological functions. As a result, intensive nutrition nervous tissue has a huge role in the life of the body. The blood supply to the brain is carried out by two internal carotid and two vertebral arteries.

Arterial blood supply system

Physiology human body not yet fully understood, but the biggest mystery for scientists remains the brain, which is always active, even if a person is in a state of rest and sleep. The blood supply to the brain is provided by two systems:

1. The vertebral arteries, which begin in the subclavian, pass into the transverse processes of the cervical vertebrae and, in the region of the first of them, leave this canal, entering the foramen magnum in the skull. Here the PA are at the base medulla oblongata. At the border of the latter and the bridge of the brain, the arteries listed above merge into one trunk of the basilar artery. At the border of the bridge, it is divided into a pair of rear cerebral arteries.

If there are pathologies in the cervical region, squeezing of the artery is often observed, which sometimes leads to irreversible consequences.

1. The internal carotid artery separates from the common carotid artery, which in turn separates from the aorta and subclavian artery. Due to this, normal conditions for blood flow are created in the system of the left artery.

When a thrombus detaches from the left region of the heart, it often passes into the left carotid artery than into the right one, since there is a direct communication with the aorta. The ICA enters the skull through the canal of the same name.

A diagram of the blood supply to the brain can be seen below.

The connection of both systems is due to the arterial circle of the cerebrum, which is otherwise referred to as the circle of Willis and is formed due to the following blood supply elements:

• cerebral posterior (vertebral);
• connecting back (internal carotid arteries);
• cerebral middle (internal carotid arteries);
• cerebral anterior (internal carotid arteries);
• connecting anterior (internal carotid arteries).

The purpose of the arterial circle of the large brain is to support proper blood flow to the brain, which is necessary if there is a violation in one of the arteries.

The system for transporting substances from the capillary to the nervous tissue is called the "blood-brain barrier", which prevents pathogenic factors (toxins, microbes, etc.) from entering the brain.

In the normal state of the barrier, substances such as:

• iodine compounds;
• immune bodies;
• salt;
• antibiotics.

Thus, medicines containing the substances listed above in their composition cannot affect the nervous system.

At the same time, they are able to overcome the blood-brain barrier:

• morphine;
• alcohol;
• tetanus toxin;
• chloroform.

To ensure that drugs used to treat infectious diseases of the brain could easily overcome this barrier, they should be introduced into the fluid that surrounds the brain. This process is carried out due to a puncture in the lumbar region of the spinal column or in the area under the back of the head.

The outflow of blood is carried out through the veins, which flow into the sinuses of the dura mater. They are slit-like canals in the medulla connective tissue. Their peculiarity lies in the fact that their clearance is always open in any conditions. This ensures a stable outflow of blood and does not allow it to stagnate. Through the sinuses, venous blood enters the jugular foramen, located in the cranial base, from where the jugular vein begins. Through it, blood flows into the superior vena cava.

The functionality of the arteries that make up the circle of Willis

The anterior cerebral artery supplies blood to the following areas:

• upper section of the postcentral and precentral gyri;
• cerebral cortex;
• olfactory tract;
• basal and internal frontal lobe;
• white matter of the parietal and frontal lobes;
• head and outer part of the caudate nucleus;
• part of the corpus callosum;
• section of the leg of the internal capsule;
• part of the lenticular nucleus.

The middle cerebral artery is responsible for the blood supply to the following areas:

• cerebral cortex;
• part of the lenticular and caudate nuclei;
• white matter of the surface of the cerebral hemispheres;
• in the temporal lobe of the center of Wernicke;
• visual radiance;
• parietal lobe;
• part of the frontal convolutions and lobes.

The posterior cerebral artery supplies the following areas:

• cerebral cortex;
• white matter;
• hypothalamus;
• leg of the brain;
• part of the thalamus;
• caudate nucleus;
• corpus callosum;
• bunch of Graziola;
• quadrigemina.

The vertebral arteries feed the following cerebral zones:

• sections of the cerebellum;
• medulla;
• spinal cord.

The posterior inferior cerebellar artery provides blood supply to the following departments:

• posterior inferior cerebellum;
• part of the medulla oblongata.

An interesting fact is that there is no portal system in the blood supply to the brain. That is, the branches of the circle of Willis do not penetrate the medulla, as is usually the case in life. important organs body. They spread along the cerebral surface, branching into thin branches at right angles. This fact determines the uniform distribution of blood supply. Therefore, there are no large vessels in the brain, but only capillaries and small arteries.

Nevertheless, there are large arteries in the head, which are located on the cerebral surface in the arachnoid membrane. Their location is fixed, since the vessels are not only suspended on trabeculae, but also maintained at a specific distance relative to the brain.

Peculiarities

An interesting fact is that hemodynamics and changes in it do not affect blood circulation, since it contains self-regulation mechanisms.

The blood circulation of the gray matter has a greater intensity in comparison with the white. The most saturated blood flow is manifested in babies, whose age has not yet reached the year. A newborn baby has a greater blood supply than an adult. As for the elderly, in this category of people it is reduced by twenty percent, and sometimes even more.

Control over this process occurs in the nervous tissue, and it is due to metabolism. Centers for the regulation of nervous activity operate throughout life, without stopping their functioning even during sleep.

The intracerebral structure of capillaries has some features, namely:

1. A thin elastic membrane surrounds the capillaries, as a result of which they cannot be stretched.
2. Capillaries do not have Roger cells that can contract.
3. Transudation and absorption is carried out at the expense of precapillaries and postcapillaries.

Different blood flow and pressure in the vessels cause extravasation of fluid in the precapillary and absorption in the postcapillary.

This whole complex process makes it possible to have a balance between absorption and transudation without the participation of the system that the lymph forms.

Pregnancy has a special effect on the blood supply of the whole organism and the brain in particular, during which medicines are contraindicated, otherwise the fetus may have pathologies.

Violation of the blood supply

A person can independently check the blood supply in the brain - normally, the skin of the scalp should move freely in all directions.

Temporary disturbances in blood flow can occur under the influence of various factors. For example, with osteochondrosis, the cervical vertebra presses down on the vessels, and this is the cause of migraines. An increase in blood flow can also slow down blood pressure, tension and excitement. In such a situation, the symptoms are often replenished with loss of consciousness, vomiting and sensation. Most often, it is the asymmetry of blood flow through the arteries of the spine that provokes a violation of blood supply.

If the blood supply is insufficient, then there is a low percentage nutrients and oxygen in neurons, which leads to brain damage and development pathological processes. An electroencephalographic study can reveal such conditions occurring in the brain.

Focal signs of pathological disorders imply the development of the following conditions:

• hemorrhagic stroke;
• cerebral infarction;
• hemorrhages in the hypothecal area.

Such conditions appear in the form of the following clinical picture:

• epilepsy;
• decreased sensitivity;
• intellectual impairment;
• problems with coordination of movements.

When the blood supply to the brain is disturbed, a person feels such conditions subjectively, but they are also accompanied by objective neurological symptoms, which include:

• headache;
• paresthesia;
• dizziness;
• problems with the functioning of the organs responsible for sensitivity.

Circulatory disorders are divided into three stages:

1. Initial.
2. Acute.
3. Chronic.

Acute violation of blood circulation manifests itself in the form of strokes, hemorrhages and other disorders. TO chronic condition encephalopathy and dyscirculatory myelopathy can be attributed.

The clinical picture of circulatory disorders in the brain is as follows:

• headache;
• dizziness;
• red face;
• pain in the eye area;
• a common symptom is tinnitus;
• nausea;
• convulsions;
• turning the head in the direction of the lesion worsens the condition;
• confusion.

An interesting fact is that pain syndrome tends to increase.

Often these conditions are supplemented by the following symptoms: chills, fever and high blood pressure.

Causes

The following pathologies can affect poor blood circulation in the brain:

1. Atherosclerosis, which occurs more often in the elderly and in those who suffer from impaired functionality of the heart vascular system. During this process, sclerotic plaques collect in the arteries, which significantly impede blood circulation.
2. Curvature of the spine, as well as a pinched muscle as a result, can also disrupt blood circulation.
3. Hypertension.
4. Stressful situations can also reduce blood flow.
5. Liquor also has a significant effect on the blood supply.
6. Surgery or trauma to the skull.
7. Injured spine.
8. Wrong venous return blood from brain tissue.

Regardless of the reasons that led to the difficulty of microcirculation, the consequences are reflected not only in the brain, but also in the work of internal organs.

Elimination of disorders of blood circulation in the brain

Circulation can improve during deep breathing, due to which much more oxygen enters the tissues. To achieve a significant effect, you should use simple exercise after consulting with the attending physician.

A stable blood supply to the brain and spinal cord can only be achieved through healthy blood vessels.

Thus, in order to achieve what you want, you need to do and nourish the brain. For this purpose, those products that contribute to the removal of cholesterol should be used.

More often, in order to normalize the condition, it is necessary to take appropriate medications, but they are prescribed exclusively by a doctor. It should be borne in mind that there is no such drug that could cope with the problem alone. Treatment includes a complex of drugs of various directions:

1. Vasodilators, which act on smooth muscles, relaxing it, due to which the lumen of the vessels expands, which can increase blood flow (Nimodipine or Cinnarizine).
2. Nootropics that have their effect due to the ability to improve metabolism. They stimulate blood flow and create resistance to existing hypoxia.
3. Antithrombotic, which are necessary in case of detection of plaques or atherosclerosis. They are able to seal the thin walls of blood vessels and at the same time eliminate plaques.

According to neurology, sometimes the use of sedatives is required.

Based on the results of the diagnosis, fibrinolytics, anticoagulants and antiplatelet agents may be prescribed.

It is also possible to improve the blood supply to the head due to Ayurvedic remedies, dietary supplements and homeopathic preparations. At the initial stage, folk remedies, which are tinctures and decoctions, also help. medicinal herbs as well as massage.

The famous homeopath Valery Sinelnikov writes in his writings that a headache is a sign that a person is doing something wrong in his life, and in order to get rid of such unpleasant symptoms, one should reconsider one's outlook on life, stop being hypocritical and start treating others. many situations are easier.

The nutrition of the medulla is carried out with the help of the circulatory system of the head and neck, which supplies arterial blood enriched with oxygen and minerals and frees it from decay products and toxins, taking away venous blood. The medulla requires twenty times more energy than the corresponding mass of muscle tissue. Malfunctions in the work of arteries and veins are partially compensated and a person may not feel that the cerebral blood flow is not working in full.

If the circulatory system fails to provide the brain with a sufficient amount of blood, oxygen starvation occurs, expressed through headaches, memory impairment, and fatigue.

Circulatory system of the head and neck

Blood from the heart to the head moves through large and branched main arteries:

• internal carotid (steam room);
• basilar.

They go around the brain, part of the spinal cord, capturing the cerebellar region.

The nutrition of the medulla is carried out through the internal paired vertebral and carotid arteries.

Arteries that feed the brain

Through channels temporal bone the carotid arteries, entering the cranial cavity, branch into the ophthalmic arteries, which supply the organs of the orbit with blood.

Each carotid artery has three branches:

1. 1. Anterior, supplying the cerebral hemispheres, the parietal zone and part of the frontal zone.
2. 2. The middle one, passing through the lateral (Sylvian) groove, dividing into branches covering the cerebral cortex almost along the entire outer surface, including the parietal, frontal, temporal lobes. This artery feeds the main mass of gray subcortical formations and analyzer departments: the motor, skin, and cortical centers of speech.
3. 3. Posterior, supplying blood to the lower part of the temporal and occipital lobes.

The vertebral arteries entering the cranial cavity through the foramen magnum form the basilar artery. Passing along the midline of the brain stem, it branches to the cerebellum, inner ear and brain bridge. At the anterior margin of the cerebral pons, the basilar artery bifurcates into the posterior cerebral arteries, which carry blood to the cortex of the posterior hemispheres.

In case of failure in blood circulation due to the formation of blood clots, aneurysms, etc., the cerebral arteries are connected to the circle of Willis, located in the region of the brain stem. The right and left cavernous sinuses form the corresponding closed venous sinus.

A branch that separates from the external carotid artery and is called the middle meningeal artery approaches the dura mater. The bones of the cranium have its imprints in the form of furrows.

The arterial branches of the surface of the brain penetrate deep into the medulla, forming a dense vascular network. The anterior horns are supplied most abundantly in the spinal cord.

The cervical part of the spinal cord is supplied by the right and left branches of the vertebral arteries, and its membranes are supplied with blood from several nearby vessels. The left and right vertebral arteries, which merge into the anterior spinal artery, form one thin branch each. These branches descend through the anterior sulcus of the medulla oblongata and then the spinal cord. Both vertebral arteries in the skull branch off the posterior spinal arteries, passing near the nerve roots. Their purpose is to supply blood to the spinal cord and its roots. The supply of blood to the spinal cord is also provided by small branches coming from the ascending cervical, intercostal and lumbar arteries.

Due to the greater activity of the gray matter of the brain and spinal cord, its blood supply is better and more abundant than that of the white matter, therefore, the small vessels of the brain tissue in the gray matter look like a dense narrow-loop network, and in the white - wide-loop.

Venous network

The veins of the brain have a different structure than the veins of other organs. Their walls are thinner and more delicate and do not have valves. The cerebral veins are separated from the arteries.

To remove carbon dioxide and waste substances from the upper and lower layers of the brain and cervical regions, venous collectors, the sinuses, are used. They lack valves and a muscular membrane, and a rigid structure helps to improve the outflow of venous blood.

The veins of the brain are divided into superficial and deep. The superficial veins of the brain from both hemispheres flow into the superior sagittal sinus throughout its entire length. Deep veins merge under the corpus callosum and form the left and right internal veins of the brain, which flow into the large (galenic) vein of the brain, continuing in the rectus venous sinus.

The veins of the head and neck contain approximately seventy-five percent of the blood that has entered these departments, the condition of the venous network is of great importance for the stable functioning of the brain and the whole organism as a whole.

Types of intervascular connections

The veins and arteries of the brain and neck are interconnected by intervascular connections - anastomoses, which play an important role in adapting blood circulation in the event of pathologies.

Intervascular connections are divided into the following types:

1. 1. Arterio-arterial anastomoses that connect the cerebral arteries. When clogging some vessels of the neck and head, they serve as bypass routes for blood flow. With blockage of the main arteries, disturbances in blood circulation are not replenished.
2. 2. Arterio-venular anastomoses are connections between veins and small arteries - arterioles. Their function is to redirect the flow of blood into the veins when necessary.
3. 3. Veno-venous anastomies, which are a large number of connections between veins necessary to ensure a good outflow of blood.

Vascular Anatomy

The anatomy of the vessels of the neck and head is circulatory system composed of arteries and veins.

Vessels have a three-layer structure that provides adaptation to possible internal changes in the body. Each layer has its own function.

Artery structure

1. The intima of the vessel - the inner layer in direct contact with the blood, called the endothelium, is characterized by the absence connective tissue. It has a fragile structure, easily damaged. The release by the surface of this layer of substances that prevent the process of blood clotting inside the artery (the formation of blood clots) is its main function. From the blood flowing through the intima, the vessel receives oxygen, mineral and organic compounds due to the slowdown in blood flow near the very walls relative to the total flow.

2. The middle layer is a muscle layer and connective tissue that serve as a flexible frame for the vascular system. The alternation of relaxation and tension of muscle fibers expands and constricts blood vessels, depending on the situation. The middle layer adjusts the speed of blood flow and blood pressure.

3. Vascular adventitia - the outer layer, which is a thick membrane consisting of connective tissue. It performs a strengthening function. Others passing through this layer blood vessels- arteries, veins, nerve endings- enriched with essential biological substances and oxygen.

In the inner layer, consisting of muscle cells, there are no elastic membranes, and the semilunar valves, which prevent the backflow of blood, are located at a short distance from each other throughout the entire length of the vessel.

The human skull is hermetically sealed, which creates special conditions for cerebral circulation. Blood flows through the vessels in an even stream, there is no pulsation and the brain remains motionless both during sleep and in a state of activity. The skull not only protects the brain from damage, but also completely dampens the pulse waves in the vessels of the brain and creates better conditions and peace for the work of a vital organ.

Cerebral circulation is an independent functional system, with its own characteristics of the morphological structure and multilevel mechanisms of regulation. In the process of phylogenesis, specific unequal conditions for the blood supply to the brain were formed: direct and fast carotid (from the Greek karoo - “I put you to sleep”) blood flow and a slower vertebral blood supply provided by the vertebral arteries. The volume of circulatory deficit is determined by the degree of development of the collateral network, while the most discriminated are the subcortical areas and cortical fields of the cerebrum, which lie at the junction of the blood supply pools.

The arterial system of cerebral blood supply is formed from two main vascular pools: carotid and vertebrobasilar.

The carotid pool is formed by the carotid arteries. Common carotid artery with right side begins at the level of the sternoclavicular joint from the brachiocephalic trunk, and on the left departs from the aortic arch. Further, both carotid arteries go up parallel to each other. In most cases, the common carotid artery at the level of the upper edge of the thyroid cartilage (III cervical vertebra) or the hyoid bone expands, forming the carotid sinus (sinus caroticus, carotid sinus), and is divided into external and internal carotid arteries. The external carotid artery has branches - the facial and superficial temporal arteries, which in the region of the orbit form an anastomosis with the system of internal carotid arteries, as well as the maxillary and occipital arteries. The internal carotid artery is the largest branch of the common carotid artery. When entering the skull through the carotid canal (canalis caroticus), the internal carotid artery makes a characteristic bend with a bulge upward, and then, passing into the cavernous sinus, forms an S-shaped bend (siphon) with a bulge forward. The permanent branches of the internal carotid artery are the supraorbital, anterior cerebral and middle cerebral arteries, posterior communicating and anterior choroidal arteries. These arteries provide blood supply to the frontal, parietal and temporal lobes and are involved in the formation of the cerebral arterial circle (circle of Willis).

Between them there are anastomoses - the anterior communicating artery and cortical anastomoses between the branches of the arteries on the surface of the hemispheres. The anterior communicating artery is an important collector connecting the anterior cerebral arteries, and hence the internal carotid artery systems. The anterior communicating artery is extremely variable - from aplasia ("dissociation of the circle of Willis") to a plexiform structure. In some cases, there is no special vessel - both anterior cerebral arteries simply merge in a limited area. The anterior and middle cerebral arteries are significantly less variable (less than 30%). More often, this is a doubling of the number of arteries, anterior trifurcation (joint formation of both anterior cerebral arteries and the middle cerebral artery from one internal carotid artery), hypo- or aplasia, and sometimes insular division of the arterial trunks. The supraorbital artery arises from the medial side of the anterior bulge of the carotid siphon, enters the orbit through the optic nerve canal, and divides into its terminal branches on the medial side of the orbit.

Vertebrobasilar basin. Its bed is formed from two vertebral arteries and the basilar (main) artery (a. basilaris) formed as a result of their merger, which then divides into two posterior cerebral arteries. The vertebral arteries, being branches of the subclavian arteries, are located behind the scalene and sternocleidomastoid muscles, rising to the transverse process of the VII cervical vertebra, go around the latter in front and enter the canal of the transverse processes formed by holes in the transverse processes of the VI-II cervical vertebrae, then go horizontally backwards, bending around the back of the atlas, form an S-shaped bend with a bulge backwards and enter the foramen magnum of the skull. The fusion of the vertebral arteries into the basilar artery occurs on the ventral surface of the medulla oblongata and the pons above the clivus (clivus, Blumenbach clivus).

The main bed of the vertebral arteries often branches, forming paired arteries that supply the trunk and cerebellum: the posterior spinal artery (the lower part of the trunk, the nuclei of the thin and wedge-shaped bundles (Gaulle and Burdakh)) , the anterior spinal artery (dorsal sections of the upper part of the spinal cord, ventral sections of the trunk , pyramids, olives), posterior inferior cerebellar artery (medulla oblongata, vermis and rope bodies of the cerebellum, lower poles of the cerebellar hemispheres). The branches of the basilar artery are the posteromedial central, short circumflex, long circumflex and posterior cerebral arteries. Paired long circumflex branches of the basilar artery: inferior anterior cerebellar artery (bridge, upper parts of the medulla oblongata, region of the cerebellopontine angle, cerebellar peduncles), superior cerebellar artery ( midbrain, tubercles of the quadrigemina, the base of the legs of the brain, the area of ​​\u200b\u200bthe aqueduct), the labyrinth artery (the area of ​​\u200b\u200bthe cerebellopontine angle, the area of ​​\u200b\u200bthe inner ear).

Deviations from the typical variant of the structure of the arteries of the vertebrobasilar basin are common - in almost 50% of cases. Among them are aplasia or hypoplasia of one or both vertebral arteries, their non-fusion into the basilar artery, low connection of the vertebral arteries, the presence of transverse anastomoses between them, and asymmetry in diameter. Options for the development of the basilar artery: hypoplasia, hyperplasia, doubling, the presence of a longitudinal septum in the cavity of the basilar artery, plexiform basilar artery, insular division, shortening or lengthening of the basilar artery. For the posterior cerebral artery, aplasia, doubling when departing from the basilar artery and from the internal carotid artery, posterior trifurcation of the internal carotid artery, originating from the opposite posterior cerebral artery or internal carotid artery, and insular division are possible.

Deep subcortical formations, periventricular areas are supplied with blood by the anterior and posterior villous plexuses. The former is formed from short branches of the internal carotid artery, the latter is formed by short arterial trunks, perpendicularly extending from the posterior communicating arteries.

The arteries of the brain differ significantly from other arteries of the body - they are equipped with a powerful elastic membrane, and the muscle layer is developed inhomogeneously - sphincter-like formations are naturally found in the places of vascular division, which are richly innervated and play an important role in the regulation of blood flow. With a decrease in the diameter of the vessels, the muscle layer gradually disappears, again giving way to elastic elements. The cerebral arteries are surrounded by nerve fibers coming from the superior, intermediate (or stellate) cervical sympathetic ganglia, branches from the C1-C7 nerves, which form plexuses in the medial and adventitial layers of the arterial walls.

The venous system of the brain is formed from superficial, deep, internal cerebral veins, venous sinuses, emissary and diploic veins.

The venous sinuses are formed by the splitting of the dura mater, which has an endothelial lining. The most constant are the superior sagittal sinus, located along the upper edge of the falx cerebrum; the lower sagittal sinus, located in the lower edge of the falx cerebrum; direct sine - continuation of the previous one; the straight and superior merge into paired transverse sinuses on the inner surface of the occipital bone, which continue into the sigmoid sinuses, ending at the jugular foramen and giving blood to the internal jugular veins. On both sides of the Turkish saddle there are paired cavernous sinuses, which communicate with each other by intercavernous sinuses, and with sigmoid sinuses through stony sinuses.

The sinuses receive blood from the cerebral veins. Superficial superior veins from the frontal, parietal, and occipital lobes bring blood into the superior sagittal sinus. The superficial middle cerebral veins flow into the superior stony and cavernous sinuses, which lie in the lateral grooves of the hemispheres and carry blood from the parietal, occipital, and temporal lobes. Blood enters the transverse sinus from the inferior cerebral veins. The deep cerebral veins collect blood from the choroid plexuses of the lateral and third ventricles of the brain, from the subcortical regions, the corpus callosum and flow into the internal cerebral veins behind pineal gland, and then merge into an unpaired great cerebral vein. The rectus sinus receives blood from the great cerebral vein.

The cavernous sinus receives blood from the superior and inferior ophthalmic veins, which anastomose in the periorbital space with tributaries of the facial vein and the pterygoid venous plexus. The labyrinthine veins carry blood to the inferior petrosal sinus.

Emissary veins (parietal, mastoid, condylar) and diploic veins have valves and are included in the provision of transcranial outflow of blood with increased intracranial pressure.

Syndromes of lesions of the arteries and veins of the brain. The defeat of individual arteries and veins does not always lead to pronounced neurological manifestations. It was noted that for the occurrence of hemodynamic disorders, it is necessary to narrow the large arterial trunk by more than 50% or multiple narrowing of the arteries within one or more basins. However, thrombosis or occlusion of some arteries and veins have a bright specific symptomatology.

Violation of blood flow in the anterior cerebral artery causes movement disorders of the central type contralaterally on the face and limbs (most pronounced in the leg and shallow in the arm), motor aphasia (with damage to the left anterior cerebral artery in right-handed people), gait disturbance, grasping phenomena, elements of " frontal behavior.

Violation of blood flow in the middle cerebral artery causes contralateral central paralysis, predominantly of the “brachiofacial” type, when motor disorders are more pronounced on the face and in the hand, sensitive disorders develop - contralateral hemihypesthesia. In right-handed people with damage to the left middle cerebral artery, there is a mixed aphasia, apraxia, and agnosia.

When the trunk of the internal carotid artery is damaged, the above disorders manifest themselves more clearly and are combined with contralateral hemianopia, impaired memory, attention, emotions, and disorders of the motor sphere, in addition to the pyramidal nature, can acquire extrapyramidal features.

Pathology in the basin of the posterior cerebral artery is associated with loss of visual fields (partial or complete hemianopsia) and, to a lesser extent, with disorders of the motor and sensory spheres.

The most total are violations in the occlusion of the lumen of the basilar artery, manifested by the syndrome of Filimonov - "locked man". In this case, only the movements of the eyeballs are preserved.

Thrombosis and occlusion of the branches of the basilar and vertebral arteries are manifested, as a rule, by alternating stem syndromes of Wallenberg-Zakharchenko or Babinsky-Najotte with damage to the posterior inferior cerebellar artery; Dejerine - with thrombosis of the medial branches of the basilar artery; Miyar - Gubler, Brissot - Sicard, Fauville - long and short envelope branches of the basilar artery; Jackson - anterior spinal artery; Benedict, Weber - the posterior cerebral artery, the posterior villous artery of the intercostal branches of the basilar artery.

Manifestations of thrombosis of the venous system of the brain, with rare exceptions, do not have a clear topical attachment. If the venous outflow is blocked, then the capillaries and venules of the affected drainage zone swell, which leads to the occurrence of congestive hemorrhages, and then large hematomas in the white or gray matter. Clinical manifestations– cerebral symptoms, focal or generalized seizures, disc edema optic nerves and focal symptoms suggestive of damage to the cerebral hemispheres, cerebellum, or compression of the cranial nerves and brainstem. Thrombosis of the cavernous sinus can be manifested by damage to the oculomotor, abducens, and trochlear nerves (syndrome of the outer wall of the cavernous sinus, Foix's syndrome). The occurrence of carotid-cavernous anastomosis is accompanied by pulsating exophthalmos. Lesions of other sinuses are less manifest.

The blood supply to the brain is carried out through two carotid and two vertebral arteries. Located in the thickness of the neck, these vessels reach the base of the skull and penetrate into its cavity, forming a closed arterial ring at the base of the brain.

From the anatomical and clinical-radiological point of view, it is advisable to isolate the extra- and intracranial sections of the arteries.

We will analyze the “classical” version of the structure, and then dwell on a number of basic anatomical variants, given that the morphological organization of cerebral vessels in more than 50% of cases differs from the type that is considered normal: individual arteries are sometimes absent or are sharply hypoplastic, the features of their discharge, branching and anastomosis, the presence of additional and persistent vessels are noted. This plays an important role, since it largely depends on the structural features of the arterial system of the brain whether a brain lesion will develop under the created pathological conditions, what will be its degree, localization and clinical symptoms.

I. Extracranial arteries

TO extracranial arteries include all vessels and vascular segments that carry blood towards the head between the heart and the base of the skull. Although it should be noted that for some pathological conditions these arteries can change the direction of flow and be included in the blood supply of the upper limb. The extracranial arteries include: the aortic arch before the left subclavian artery originates, the common carotid artery, the brachiocephalic trunk, the proximal subclavian arteries before the vertebral arteries originate, the common carotid artery, the internal carotid artery and the vertebral artery before they enter the cranial cavity.

/. carotid system.

The brachiocephalic trunk (truncus brachiocephalicus) is an unpaired artery extending from the aortic arch and heading obliquely to the right and up. Anterior to it is the left innominate vein, the thymus gland, and behind it is the trachea. The brachiocephalic trunk does not give branches and, at the level of the right sternoclavicular articulation, divides into the right common carotid and subclavian arteries. In some cases, another third branch departs from it - the median artery of the thyroid gland, which goes up the anterior surface of the trachea to the lower pole of the thyroid gland.

The common carotid artery (a. carotis communis) (OCA) on the right departs from the brachiocephalic trunk. The left common carotid artery departs from the aortic arch at its highest point - at the place where the brachiocephalic trunk originates. Both arteries pass to the neck behind the sternoclavicular joint between the legs of the sternocleidomastoid muscle. The CCA runs lateral to the trachea and larynx, posterior to and medial to the jugular veins. Internal jugular vein, the CCA and the vagus nerve are located in the same vagina and form the vascular bundle of the neck, posterior to which lies cervical region sympathetic trunk. The sternocleidomastoid muscle covers the common carotid artery in front. The posterior surface of the right CCA is adjacent to the scalene muscles, and the left, in addition, also to the protruding edge of the esophagus. At the level of the upper edge of the thyroid cartilage, the CCA expands, forming a bifurcation, and divides into

internal (ICA) and external (ECA) carotid arteries. In some cases, the ascending artery of the pharynx departs from the bifurcation. The division of the OSA can occur on various levels neck - at its base, in the middle or above the thyroid cartilage. The level of bifurcation is extremely variable: 1% - at the level C p, 16% - C w, 66% - C IV, 16% - C v , 1% - C vr OCA does not give a single branch before its division . Usually, the artery expands at the bifurcation into the so-called carotid bulb, which extends into the ICA. In the outer layer of the bulb there are sensitive nerve endings, the irritation of which causes a slowdown in the work of the heart, a decrease in blood pressure, and expansion of peripheral vessels. This area is called the carotid sinus reflex zone. Its irritation can be observed with rough palpation of the vessel at this level, as well as during angiography (arterial puncture, para-arterial injection of a contrast agent).

The first segment of the ICA usually passes outside or outside and posterior to the ECA, the angle of divergence is largely determined by the age and length of the vessels. Sometimes these vessels diverge in the form of a candelabra. Shortly after the bifurcation, the ICA again approaches the ECA, walks side by side, and before entering the carotid canal, makes a medial turn. In the case where the ICA departs posterior to the ECA, it then loops around the ECA. The ICA does not branch until it enters the cranial cavity.

The ECA, after departing from the common carotid artery, goes up and almost immediately begins to give off branches. Then it goes along the posterior edge of the lower jaw and, at the level of the articular process of this bone, divides into two terminal branches: the superficial temporal and internal maxillary arteries. All branches of the NSA are divided into the following:

• 1) front -- a. thyreoidea superior, a. lingualis, a. maxillaris externa;
• 2) rear -- a. sternoclaidomastoidea, a. occipitalis, a. auricularis posterior;
• 3) medial -- a. pharyngea ascendens;
• 4) final -- a. temporalis superficialis, a. maxillaris interim.

The main significance of these branches, from a neurosurgical point of view, is that in case of occlusion of the common or internal carotid artery in the neck, they can take part in the collateral blood supply to the brain.

2. Vertebral-basilar system.

The subclavian artery departs to the left directly from the aortic arch, to the right - from the brachial trunk. Coming out chest cavity through the top hole chest, the subclavian artery goes around the dome of the pleura, located in the interscalene triangle behind the anterior scalene muscle. Then the artery goes under the clavicle, comes to the 1st rib and bends over it. In the subclavian artery, three sections are distinguished: 1 - before it enters the gap between the scalene muscles, 2 - throughout the interscalene gap, and 3 - from the exit point of the artery from the interscalene gap to the lower edge of the 1st rib. In the 1st section, the vertebral artery, the internal artery of the mammary gland and the thyroid-cervical trunk depart, in the 2nd - the costal-cervical trunk and in the 3rd - the transverse artery of the neck.

The vertebral artery (VA) is the first branch of the subclavian, although sometimes it branches directly from the aortic arch (4% of cases on the left and very rarely on the right). After departing from the highest point of the subclavian arch or its posteromedial part, the VA rises anterior to the scalene muscle, wriggling slightly or making an S-shaped bend (VI segment) when entering the foramen of the transverse process C V | (90% of cases), less often C v (5% of cases) and then goes almost vertically upward through the holes in the transverse processes of the vertebrae (V2 segment). Having left the foramen C and, it turns laterally and again goes almost vertically between the axis and the atlas or turns outward before entering the transverse process of the atlas at an angle of 45°. Coming out of the hole in the transverse process of the atlas, the vessel goes back

about 1 cm posterior to the atlas, then turns medially (atlas loop -- V3 segment). The artery then gives off its muscular branches, which anastomose with the branches of the occipital artery that originate from the ECA (occipital-vertebral anastomosis). Posteriorly and medially from the atlanto-occipital articulation, the VA passes through the atlanto-occipital membrane, the V4 segment pierces the dura and arachnoid membranes.

In addition to the occipital-vertebral anastomosis, PA forms anastomoses with branches of the thyrocervical and costocervical trunks. On average, their diameter is 3.5 mm (1.5-5 mm). The right and left VA have the same diameter in about 25% of cases, usually the left FA is wider than the right one. In 10% of observations, a small diameter of the vessel is noted - its hypoplasia.

P. Intracranial vessels

IN the base areas approach the brain and communicate with each other all 4 arterial highways supplying it with blood: the anterior - internal carotid and posterior - vertebral arteries.

carotid system (Fig. 1.22).

The ICA enters the cranial cavity through the carotid foramen (foramen caroticum), which is medially posterior to the jugular foramen (foramen jugularis). It passes through the canal in the temporal bone (temporal part) and bends twice in it at an angle of 90 ° corresponding to the bends of the canal

Rice. 1.22. Anatomy of the vessels of the carotid system (quoted by E. Zlotnik, 1973).

but -- lateral projection: 1 - siphon of the internal carotid artery; 2 - ophthalmic artery; 3 -- ascending part of the anterior cerebral artery (A2); 4 -- arch of the anterior cerebral artery around the knee of the corpus callosum (A3); 5 - pericallosal artery; 6 -- fronto-pole artery; 7 -- calles-marginal artery; 8 -- ascending branches of the middle cerebral artery; 9 -- posterior parietal artery; 10 - angular artery; 11 -- posterior temporal artery; 12 - anterior villous artery; 13 -- posterior communicating artery, b -- direct projection: 1- siphon of the internal carotid artery; 2 -- proximal segment of the anterior cerebral artery (A1); 3 -- fronto-pole artery; 4 - pericallosal artery; 5 -- calles-marginal artery; 6 -- proximal segment of the middle cerebral artery (Ml); 7 -- posterior temporal artery; 8 -- posterior parietal artery; 9 - angular artery; 10 - lenticulo-striatal arteries; 11 - anterior villous artery.

Coming out through a torn hole (foramen lacerum), it goes for a short distance almost vertically in the cavernous sinus, located outward from the main bone (cavernous part - C5 segment), then turns anteriorly and upward - C4 segment, and then again posteriorly under the anterior sphenoid process - segment NW. The ICA then leaves the cavernous sinus and passes below the optic nerve in the subarachnoid cisternal space (cisternal C2). Its final part - segment C1 - goes posteriorly and laterally to the division into the middle and anterior cerebral arteries. On angiograms in the lateral projection, the cavernous and supraclinoid segments of the ICA have the shape of an S-shaped bend, which is called the ICA siphon. There are double, ordinary and straightened types of siphon. The most common is a double siphon, in which, in addition to the posterior (corresponding to the turn of the artery into the cavernous sinus) and anterior (the transition point of the subclinoid part of the ICA into the supraclinoid) arcuate flexures, there is also a third arcuate flexure posterior to the distal part of the supraclinoid segment. With an ordinary siphon, there is no third bend. The straightened siphon is a variation of the ordinary one and is characterized by a steep anterior rise of the supraclinoid segment of the ICA. Knowing the shape of the siphon is essential for topical diagnosis. volumetric formations parasellar region.

The ophthalmic artery originates from the C2-C3 segment, the posterior communicating artery (PCA) from the C1 segment, with the exception of 10% of cases when the posterior cerebral arteries (PCA) originate directly from the ICA. The diameter of the ICA averages 2.8-3.3 mm. Very great importance in the diagnosis is attached to the ophthalmic artery. It usually originates from the posterior-medial part of the anterior loop of the carotid siphon (segments C2, C3), turns medially from the ICA, and enters the optic canal below and medially from the optic nerve. Then it goes to the superomedial part of the orbit and, approaching the block, is divided into terminal branches - supratrochlear and supraorbital, which have anastomoses with the terminal branches of the ECA. It should be noted that there is also an anastomosis between the middle sheath artery, more precisely, its branch - the maxillary artery - and the branches of the ophthalmic artery.

ZSA starts from rear wall ICA at the site of its maximum posterior curvature. The artery runs posteriorly along the inner surface of the oculomotor nerve, then medially and flows into the posterior cerebral artery (PCA). Thus, the PCA is, as it were, an anastomosis between the ICA and the PCA. On its way, PCA supplies blood to nearby formations (optic chiasm, optic tract, gray tubercle).

From the posterior surface of the ICA somewhat distally to the PCA, the anterior artery of the choroid plexus departs. It goes backwards and upwards along the optic tract, enters the lateral ventricle and branches in the choroid plexus of its lower horn, supplies blood to the posterior third of the shell, the optic tubercle and the inner part of the internal capsule.

The middle cerebral artery (a. cerebri media) (MCA) departs from the C1 segment of the ICA. The length of its main trunk is on average 16.2 mm (5-24 mm), and the diameter is 2.7 mm (1.5-3.5 mm). The main trunk (Ml segment) is divided into 2 or more branches (up to 5) - the M2 segment. The division of the ICA can be loose and main. With the main type of division, the ICA continues in the MCA, and the PCA and the anterior cerebral artery (ACA) are branches, with the loose type, branching occurs at one point.

Branches of the MCA first go in the same direction as the main trunk, especially if it is short, and then in the region of the insula they branch upwards at an acute angle, some branches turn medially. This point (Sylvian point) is usually located at a distance of 30 mm from the inner surface of the scales of the temporal bone.

Depending on the direction of the branches and the area of ​​​​their blood supply, groups of anterior branches are distinguished, going to the frontal region, upper - rising to the motor and sensory regions, posterior - continuing the course of the main trunk and heading to the parietal

and the occipital lobes and the lower ones - encircling the temporal lobe from top to bottom. The artery supplies most of the lateral surface of the cerebral hemisphere and the insula.

The ACA emerges from the ICA and travels anteriorly and medially, passing over the chiasm or optic tract under the anterior perforated space, either in a straight line or in a curve (segment A1). In this segment, several perforating branches depart from it, of which the largest branch is the Heubner artery (Heubner artery). The anterior perforating arteries enter the brain through the anterior perforated space and feed the head of the caudate nucleus, the anterior part of the lentiform nucleus, and the internal and external capsules. Occasionally there is hypoplasia (4% of cases) or aplasia (1% of cases) on one side, but a slight difference in diameter between the sides is the rule. On average two PMA connected above the optic chiasm by a short anterior communicating artery (ACA), the average length of which is 2.6 mm. In 74% of cases, there is one PSA, in 10% there are two, less often plexiform or other atypical configurations are observed. Very rarely there is aplasia (0.3% of cases) or hypoplasia (9% of cases). After the anterior communicating artery PMA goes anteriorly and upward (A2) along the medial surface of the hemispheres above the corpus callosum. The part of the artery located distal to the flexure of the corpus callosum is called the pericallosal artery. It supplies blood to the medial parts of the cerebral hemispheres, the nuclei of the large brain, the corpus callosum, and partially the outer surface of the frontal and parietal lobes.

Vertebrobasilar system (Fig. 1.23).

PA after entering the subarachnoid space passes between the brainstem and clivus straight or slightly meandering or making a small loop backwards, and connects with the opposite PA, usually at the posterior edge of the bridge. The diameter of the left PA is 2.2-2.3 mm, the right one is 2.1 mm. The first major branch of the PA is the posterior inferior cerebellar artery. It is variable in its course and origin: in 10% of cases it departs from the BA, in 10% of cases one of the arteries is absent. The posterior inferior cerebellar artery runs proximally to the beginning of the BA, giving branches to the brainstem and cerebellum. The artery departs above the foramen magnum in 57% of cases, below - in 18% of cases, at the level of the opening - in 4% of cases. Often the artery makes a "caudal loop" that may reach the arch of the atlas. On average, its diameter is 1.2 mm.

The anterior spinal artery is a small branch that begins at an average distance of 5.8 mm from the junction of the vertebral arteries and reaches the anterior surface of the trunk. Its diameter is 0.4-0.75 mm.

BA is formed by the connection of the vertebral arteries and then divides into two posterior cerebral arteries. It has an average length of 30 mm (24–41 mm) and an average diameter of 3 mm (2.5–3.5 mm). Usually it is straight, but sometimes it can turn slightly to the side (10-20%). Sometimes it forms an S-shaped bend between the clivus and the brainstem.

The anterior inferior cerebellar artery originates from the lower third of the BA in about half of the cases and from the middle third in the remaining cases. It goes to the anteroinferior parts of the cerebellum, supplying them with blood. It is usually much thinner than the posterior inferior cerebellar artery.

The superior cerebellar artery usually arises from the terminal part of the BA. For the first few centimeters, it goes forward and laterally, almost parallel to the PCA. On average, its diameter is 1.9 mm. It bends over the legs of the brain and goes to the upper surface of the cerebellum, supplying it with blood.

The PCA is anatomically and functionally a border vessel between the carotid and vertebrobasilar systems. Phylo- and ontogenetically, it originates from the ICA and only later develops its relationship with AD. In about 10% of adults, the PCA departs from the ICA (the so-called posterior trifurcation of the ICA).

Rice. 1.23. Anatomy of the vertebral vessels [E. Zlotnik].

a - lateral projection: 1 - vertebral artery; 2 - the main artery; 3 -- lower posterior cerebellar artery; 4 -- superior cerebellar artery; 5 - posterior cerebral artery; 6 - temporal-occipital branches of the posterior cerebral artery; 7 - internal occipital branches of the posterior cerebral artery; 8 -- internal branches of the superior cerebellar artery;

b-- direct projection: 1 - vertebral artery; 2 - the main artery; 3 -- lower posterior cerebellar artery; 4 - superior cerebellar artery; 5 - posterior cerebral artery; 6 - internal occipital branches of the posterior cerebral artery; 7 -- temporal-occipital branches of the posterior cerebral artery; 8 -- external branch of the superior cerebellar artery.

Its first segment (P1) goes anteriorly and outward to the PCA and then turns posteriorly around the brain stem (P2), adjoining the edge of the tentorial foramen, goes up and laterally along the lower surface of the occipital lobe, giving off cortical peripheral branches that supply blood to the occipital and partially temporal shares. The diameter of P1 is 2.1 mm, P2 is 2-3.3 mm. In the initial segment, it gives off perforating branches, which, passing through the posterior perforated foramen, supply blood to the subcortical nodes, cerebral peduncles, choroid plexus III and lateral ventricles.

ZSA has many options for development. In 22% of cases, it is hypoplastic. On average, its length is 14 mm, diameter is 1.2 mm. Approximately 15% of cases have aplasia on one or both sides. It runs posteriorly and slightly laterally from the PCA to the ICA.

III. Collateral blood supply

Collateral pathways can compensate for reduced flow when a high degree of stenosis or occlusion develops in the extra- or intracranial arteries. Arteries that normally do not take part in the blood supply to the brain may be included in the blood flow and, less often, the vessels of the brain may be included in the blood supply to the upper limb (steal from the vertebral, basilar or carotid arteries with occlusion of the proximal subclavian artery or brachiocephalic trunk). The inclusion of collateral pathways and the direction of blood flow depend on the pressure gradient.

1. Orbital collaterals.

The ophthalmic artery normally receives its blood supply from the ICA, and its terminal branches anastomose with the ipsi- and contralateral ECAs. The watershed exists in the area of ​​the fronto-orbital anastomosis. In high-grade stenosis of the ICA, proximal to the origin of the ophthalmic artery, the watershed shifts from the extra- to the intraorbital region. A pronounced decrease in flow in the ICA and ECA, on the one hand, causes retrograde blood flow through the corresponding orbital arteries from the branches of the contralateral ECA (branches of the artery of the back of the nose and distal anastomoses in the region of the supratrochlear arteries).

2. Occipito-vertebral anastomoses.

Anastomoses between the branches of the occipital artery and the muscular branches of the V3 segment of the VA form the main extracranial connection between the carotid and vertebrobasilar systems. With proximal VA occlusion, occipital-vertebral anastomoses can provide perfusion of the distal site, just as with CCA occlusion and proximal ECA, the direction of blood flow can be reversed.

3. Vertebral artery as a collateral pathway.

The deficit caused by unilateral VA occlusion is compensated by a corresponding increase in flow through the opposite VA. Reversal of collateral flow through the VA can occur with occlusion of the proximal subclavian artery or brachiocephalic trunk. The flow from the PA or, more rarely, from the BA is called the subclavian steal.

4. Arterial circle of the brain (circle of Willis).

This anastomosis at the base of the brain connects the carotid systems to each other and to the vertebrobasilar system via the anterior and posterior communicating arteries.

The arterial circle is the most important system for equalizing and distributing pressure in the arteries supplying the brain. It can be extremely variable and in 3-4% of cases it is not closed. Only 20% of people have its classical configuration; in other cases, certain parts of the circle are hypoplastic. With hypo- or aplasia of one of the anterior cerebral arteries, the blood supply on the side of underdevelopment is carried out by the opposite carotid artery. Such a variant of development, in which one ICA nourishes the MCA and both ACAs, is called the anterior trifurcation of the ICA.

The posterior communicating arteries are the most variable. Often one of the arteries is smaller in diameter than the other. The variant of development, in which the PCA starts directly from the ICA, is called the posterior trifurcation.

Development options in which one of the connecting arteries is missing deserve the greatest attention. In such cases, the arterial circle of the large brain is open.