The brain is the organ most sensitive to oxygen deficiency. It is the cells of the nervous system that are the first to suffer with a decrease in the amount of energy and nutrients. To prevent this, a wide network of blood vessels approaches the brain. If the blood flow is disturbed in one of them, the other will immediately assume its function. The largest vessels are the cerebral arteries. These include the anterior, middle, and posterior cerebral arteries.
Features of the blood supply to the brain
Blood enters the brain from the two largest arteries: the internal carotid and vertebral. The carotid, in turn, is divided into the anterior and middle cerebral vessels. But before this branching, it gives another small branch into the cranial cavity - the ophthalmic artery.
The group of vessels that extend from the carotid artery is called the synocarotid basin. It supplies blood to most of the cerebral cortex, the white matter under the cortex. These vessels also supply blood to structures such as the inner capsule, corpus callosum, basal nuclei, part of the hypothalamus, and the anterior wall of the lateral ventricle.
Two vertebral arteries are combined with each other in a single basilar. And it is already divided into the left and right posterior cerebral arteries. This group of vessels was called the vertebro-basilar basin.
Thus, through the vascular system, blood flows to the brain. And she leaves him through a network of veins.
Areas of the brain that supply blood to the posterior cerebral artery (ZMA)
The branches of the vessels of the vertebro-basilar basin are divided into two subgroups: cortical and central (deep). The first carries blood to the cerebral cortex. These are such areas as the occipital and parietal regions, as well as the posterior part of the temporal lobe.
Deep branches provide blood and nutrients to the structures that are located under the cerebral cortex. These include the visual tubercle, or thalamus, the back of the hypothalamus, the tubercle nucleus, the corpus callosum (its thickening). Separate branches of ZMA go to the midbrain formations - the legs.
Good blood supply to these sites provides normal visual function, memory, sensitivity, trophism of internal organs, motor activity. With a violation of the blood flow in the ZMA, a disruption in the work of almost all structures of the posterior part of the brain occurs. This causes certain clinical manifestations, which will be discussed in the corresponding section of the article.
Collateral circulation in the brain
If there is a disturbance in blood flow in one section of the brain, compensation mechanisms are immediately turned on. Blood supply from other intact vessels increases. This is possible due to the presence of the arteries of the Willis circle.
This vascular system has a clear structure, but not everyone has them. According to various data, only 25-50% of people have all vessels of the Willis circle. In most cases, these structural abnormalities do not make themselves felt, but some still have periodic headaches or dizziness. People with abnormal development of the vessels of the Willis circle are characterized by more extensive damage to the brain in acute circulatory disorders (strokes). This is due to the fact that the violation of blood flow in one artery is poorly compensated by others.
For the majority of inhabitants it remains unclear what it is, the circle of Willis, and what is its structure. This formation consists of such arteries:
- anterior cerebral;
- posterior cerebral;
- front connecting;
- back connecting;
- inner carotid.
The vessels are connected together in the form of a heptagon. The two anterior cerebral arteries are connected by the anterior connective artery, and the internal carotid artery combines with the posterior cerebral artery through the posterior connective artery.
The Willis circle is located on the base of the brain, under the arachnoid meninges.
The classical structure of this vascular formation is considered above. But, as noted earlier, not all people have it built in this way. Therefore, answering the question of what it is, the Willis Circle, it is worth noting other options for its anatomy:
- the absence of one of the two posterior connecting arteries;
- lack of anterior connecting artery;
- a branch of the posterior cerebral from the internal carotid artery;
- the combination of the 2nd and 3rd options;
- the absence of two posterior connecting arteries;
- anterior cerebral branch from one carotid artery;
- the absence of all connective arteries;
- underdevelopment of the posterior cerebral artery.
Most often, the presence of any of the above-mentioned anomalies in the development of blood vessels makes migraine manifest itself. Discirculatory encephalopathy may also occur. This is a chronic deterioration of blood flow through the vessels of the brain, which ultimately leads to dementia.
Another pathology that is often found in the vessels of the Willis circle is aneurysm. It is a bag-like protrusion of the vascular wall. As a result, the vessel in this place may burst, and there will be hemorrhage in the brain.
ZMA structure
The vessel is conditionally divided into three parts, which are also called segments of the posterior cerebral artery. The name of each part consists of the letter "P" and a number corresponding to its location. Also, each segment is assigned a Russian-language name:
- precommunication part;
- postcommunication part;
- final, or cortical, part.
The precommunicating part (P1 segment of the posterior cerebral artery) is the part of the vessel located to the place where the posterior connecting artery enters. Branches such as the medial posterior choroidal, paramedian mesencephalic, as well as the posterior thalamoperforative artery depart from it. They carry blood to the nuclei of the thalamus and to the cranked body (its medial part).
The postcommunication part (P2 segment) is a site located after the posterior connecting artery flows into the vessel. The following branches of the posterior cerebral artery depart from it: thalamogeniculate, pedunculate perforating and lateral posterior choroidal arteries. They also supply blood to the cranked body, but its middle part. In addition, these vessels carry oxygen and nutrients to the part of the midbrain, nuclei and pillow of the thalamus, the side wall of the first and second ventricles.
The terminal portion (P3 and P4 segments) carries blood to the cerebral cortex. It gives the anterior and posterior temporal, spur and parietal-temporal branches. In most cases, blood from the final segment flows to the cortex to the sylvian groove. However, there are cases when the middle cerebral artery extends to the occipital region.
Features of the structure of ZMA in the prenatal period
The structure of the vessels of the vertebro-basilar basin during the formation of the brain is somewhat different from that in the brain of an adult. This feature is worth considering.
The posterior cerebral artery departs directly from the internal carotid. And the posterior connective artery is the proximal portion of this vessel. Further, blood in the ZMA begins to come from the main (basilar) vessel, which provides blood flow. As the brain develops in children, the posterior connective artery becomes one of the most significant "bridges" between the two vascular pools.
According to statistics, up to 30% of people have a type of ZMA structure, as in the prenatal period. That is, it is supplied with blood from the internal carotid artery. As a rule, such changes are observed only on one side. On the other, ZMA departs from the asymmetrically placed, curved shape of the main artery.
About 10% of the world's population have bilateral changes when two ZMAs depart from the internal carotid arteries. In these cases, well-developed posterior connective vessels are determined. And the basilar artery is shorter than that of other people.
Symptoms of circulatory disorders in ZMA
The clinical manifestations of impaired blood flow in ZMA depend on the location of the damage. These may be symptoms of damage to the midbrain, thalamus, occipital and parietal region of the cerebral cortex.
Also, the clinic varies depending on the type of pathology. So, a stroke is an acute circulatory disorder, so the symptoms develop suddenly and rapidly. And dyscirculatory encephalopathy, in turn, is a chronic disease. Therefore, the clinic progresses slowly, for a long time no symptoms are observed at all.
The most specific disturbance of blood flow in the posterior cerebral artery is ischemic stroke. This is a disease in which a vessel is clogged by a blood clot or embolus, which interferes with blood circulation. As a result, necrosis (death) of a part of the brain occurs.
The following groups of symptoms are distinguished:
- basilar artery apex syndrome;
- visual disturbances;
- mental disorders;
- motor disorders.
The syndrome of the apex of the main artery occurs when the blood flow in the distal part of the vessel is disrupted, before it is divided into the right and left ZMA. In this case, all brain structures that receive blood from ZMA are affected. The patientβs consciousness is disturbed up to coma, vision, psyche suffers. Motor function is often retained.
Features of visual, mental and motor disorders
Visual disturbance occurs with damage to the occipital region of the cerebral cortex, visual radiation and the cranked body. In this case, a complete loss of the field of view from the opposite side occurs. For example, if the occipital part of the cortex is affected on the right, a person is not able to see the left half with two eyes. The right field of view remains unaffected. Sometimes not a half, but a square of the field of view falls out.
If the occipital region is affected on both sides, visual impairment may be more complex. Visual hallucinations occur, the patient does not recognize familiar faces, colors. A rare pathology for circulatory disorders in the posterior cerebral artery is Anton's syndrome. In the presence of such a state, a person does not realize that he is completely blind.
Psychological disorders occur with damage to the corpus callosum and occipital lobe. A person is not able to read, while the ability to write is preserved. If a person is right-handed, such changes are possible with circulatory disorders in the left ZMA. With damage to a large area of ββthe cortex, amnesia and psychiatric disorders (delirium) occur. If there is extensive necrosis of the thalamus, the patient may develop Dejerine-Russi syndrome. It manifests itself with the following symptoms:
- violation of sensitivity (tactile, temperature, pain);
- severe pain on the entire half of the body, opposite to the location of the lesion in the thalamus;
- lack of movement on the opposite half of the body;
- involuntary spontaneous movements in the limbs;
- sensation of goosebumps, crawling flies on the skin on half the body.
On the one hand, motor disorders in the form of weakness of the upper and lower extremities are observed in 25% of patients. This symptom is called hemiparesis, and occurs from the side opposite to the location of the blockage.
Most often, the cause of motor disorders is a violation of the blood supply to the legs of the brain. However, paresis may develop without damage to this structure. In such patients, movements are impaired due to compression of the internal capsule by the edematous thalamus.
In 25% of patients, stroke in the vertebro-basilar basin imitates blockage of the vessels of the synocarotid basin. Sometimes they are difficult to distinguish from each other due to speech disorders in the patient, sensitivity disorders and motor skills. Therefore, when diagnosing blood flow disorders in the posterior cerebral artery, it is so important to use additional examination methods.
Instrumental diagnosis of stroke in ZMA
One of the methods of additional examination for the diagnosis of stroke is computed tomography (CT). This is an X-ray method, the essence of which is the layered display of organs and tissues due to the passage of x-rays through them. The disadvantage of this method is that it cannot detect cerebral ischemia in the first hours of a stroke. But early diagnosis is very important for effective therapy.
Sometimes computed tomography can be effective in the early hours. A radiologist can see a high-intensity signal in the image, which is one of the earliest signs of ischemia.
A more advanced method is CT angiography. With its help, you can determine the degree of blockage of the artery, the shape and size of the plaque. Also evaluate the options for the anatomy of the posterior cerebral artery, its relation to the surrounding brain tissue, the development of collaterals.
But the most informative method in the diagnosis of circulatory disorders is magnetic resonance imaging. This method is not related to the passage of x-rays through the human body. The image is obtained due to the presence of a magnetic field inside the tomograph, which captures the difference in the concentration of hydrogen ions in different tissues.
Magnetic resonance imaging allows you to see ischemic changes in the first hour after a vascular accident. Also, using this method, you can more accurately determine the localization and prevalence of the pathological focus. Different modes make it possible to distinguish between acute and chronic circulatory disorders.
Treatment of cerebrovascular accident
Drug therapy for blood flow disorders in the vessels of the brain depends on several factors:
- the severity of the process (acute, subacute or chronic);
- type of circulatory disturbance (ischemic or hemorrhagic);
- the presence of concomitant diseases (atherosclerosis, diabetes mellitus, arterial hypertension, etc.).
All vascular preparations to improve blood circulation in the brain can be divided into several groups:
- vasodilator, or vasodilators;
- anticoagulants and antiplatelet agents;
- nootropics;
- herbal remedies.
Vasodilators are used for both chronic and acute circulatory disorders. They effectively lower blood pressure and increase the supply of oxygen and nutrients to brain tissue.
The use of vasodilators for stroke should be very careful. The doctor prescribes them only with extremely high numbers of blood pressure. A sharp decrease in pressure is contraindicated, as it can further aggravate the patient's condition.
Preparations of the group of calcium antagonists are widely used for vasodilatation. They cause relaxation of the vessel wall and an increase in the diameter of its lumen. There are two generations of drugs. The first includes Verapamil, Nifedipine, Dilacor. The second generation: "Felodipine", "Clintiazem", "Nasoldipine".
Antiplatelet agents and anticoagulants are prescribed for the treatment and prevention of acute cerebrovascular accident. They are not able to dissolve an existing blood clot, but prevent the formation of new ones. In modern neurology, trombolytic therapy is becoming increasingly popular. The use of drugs of this group is more effective, so they can dissolve existing blood clots. In view of the high cost, these medicines are still not available in some medical institutions.
The most common antiplatelet agents:
- "Acetylsalicylic acid";
- Curantyl
- "Acuprin";
- "Ticlopidine";
- "Aspilate."
Most often in medical practice, the following anticoagulants are used:
- Heparin
- Warfarin
- Clexane
- Fragmin.
Nootropics are another group of vascular drugs to improve blood circulation in the brain. These drugs improve the metabolism in his cells, increase their resistance to oxygen deficiency. With the constant use of pills, memory improves, fatigue disappears, and cognitive functions increase.
The most effective nootropics are:
- Piracetam
- Phenibut
- Pantogam
- "Phenotropil";
- "Cerebrolysin";
- "Glycine".
Herbal medicines are actively used to improve blood circulation in the brain. Especially effective are drugs based on Ginkgo Biloba. They reduce tissue swelling, expand the cerebral vessels, increase the elasticity of their walls. Being strong antioxidants, these agents reduce the negative effects of free radicals on brain tissue. The effect of taking Ginkgo Biloba develops slowly and gradually, so the cruise should last at least three months.
Summary
The posterior cerebral artery and its branches supply almost the entire posterior part of the brain. : , , , . , , . . .
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