The brain is the most sensitive organ to lack of oxygen. It is the cells of the nervous system that are the first to suffer when the amount of energy and nutrients decreases. To prevent this, a wide network of vessels approaches the brain. If the blood flow in one of them is disturbed, the other will immediately take over its function. The largest vessels are 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 subdivided 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 branch off from the carotid artery is called the carotid sinus pool. It supplies blood to most of the cerebral cortex, the white matter under the cortex. Also, these vessels supply blood to structures such as the internal capsule,corpus callosum, ganglia basalis, part of the hypothalamus and anterior wall of the lateral ventricle.
Two vertebral arteries join together to form a single basilar artery. And it is already divided into the left and right posterior cerebral arteries. This group of vessels is called the vertebrobasilar basin.
Thus, through the vascular system, blood flows to the brain. And she departs from him through a network of veins.
Regions of the brain supplied by the posterior cerebral artery (PCA)
The branches of the vessels of the vertebrobasilar basin are divided into two subgroups: cortical and central (deep). The first carries blood to the cerebral cortex. These are its parts such as the occipital and parietal regions, as well as the back of the temporal lobe.
Deep branches provide blood and nutrients to structures that are under the cerebral cortex. These include the visual tubercle, or thalamus, the posterior part of the hypothalamus, the hypothalamic nucleus, the corpus callosum (its thickening). Separate branches of the PCA go to the formations of the midbrain - the legs.
Good blood supply to these areas ensures normal visual function, memory, sensitivity, trophism of internal organs, motor activity. When the blood flow in the PCA is disturbed, the work of almost all structures of the back of the brain is disrupted. This causes certain clinical manifestations, which will be discussed in the corresponding section of the article.
Collateral circulation in the brain
When blood flow is disturbed incompensation mechanisms immediately turn on in one part of the brain. Increases blood supply from other intact vessels. This is possible due to the presence of the arteries of the circle of Willis.
This vascular system has a clear structure, but not everyone has them. According to various data, only 25-50% of people have all the vessels of the circle of Willis. In most cases, these structural anomalies do not make themselves felt, but some still have periodic headaches or dizziness. For people with abnormal development of the vessels of the circle of Willis, more extensive brain damage is characteristic 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 most of the inhabitants it remains unclear what it is, the circle of Willis, and what is its structure. This formation consists of the following arteries:
- anterior medulla;
- posterior medulla;
- front connector;
- rear connector;
- internal carotid.
The vessels are interconnected in the form of a heptagon. The two anterior cerebral arteries are connected by the anterior communicating artery, and the internal carotid is connected to the posterior cerebral artery by the posterior communicating artery.
The circle of Willis is located at the base of the brain, under the arachnoid mater.
The classical structure of this vascular formation is discussed above. But, as noted before, not all people have it in this way. Therefore, answeringthe question of what it is, the circle of Willis, it is worth noting other options for its anatomy:
- absence of one of the two posterior communicating arteries;
- absence of anterior communicating artery;
- branch of the posterior cerebral artery from the internal carotid artery;
- combining the 2nd and 3rd options;
- absence of two posterior communicating arteries;
- branch of the anterior cerebral from one carotid artery;
- absence of all communicating arteries;
- underdevelopment of the posterior cerebral artery.
Most often, the presence of any of the above anomalies in the development of blood vessels makes itself felt migraine. Dyscirculatory encephalopathy may also occur. This is a chronic deterioration of blood flow through the vessels of the brain, which eventually leads to dementia.
Another pathology that is often found in the vessels of the circle of Willis is an aneurysm. It is a bag-like protrusion of the vascular wall. As a result, the vessel in this place can burst, and there will be a 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 has a Russian-language name:
- pre-communication part;
- post communication part;
- final or cortical part.
Pre-communication part(P1 segment of the posterior cerebral artery) is a section of the vessel located before the place where the posterior communicating artery flows into it. Branches such as the medial posterior choroidal, paramedian mesencephalic, and posterior thalamoperforating arteries depart from it. They carry blood to the nuclei of the thalamus and the geniculate body (its medial part).
The post-communication part (P2 segment) is the area located after the confluence of the posterior communicating artery into the vessel. The following branches of the posterior cerebral artery depart from it: thalamogeniculate, peduncular perforating and lateral posterior choroidal arteries. They also supply blood to the geniculate body, but its middle part. In addition, these vessels carry oxygen and nutrients to part of the midbrain, the thalamic nuclei and cushion, and the lateral wall of the first and second ventricles.
The end part (P3 and P4 segments) carries blood to the cerebral cortex. It gives rise to the anterior and posterior temporal, spur and parietotemporal branches. In most cases, blood from the terminal segment enters the cortex up to the Sylvian sulcus. However, there are cases where the middle cerebral artery extends to the occipital region.
Features of the structure of the PCA in the prenatal period
The structure of the vessels of the vertebrobasilar 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 arises directly from the internal carotid artery. The posterior communicating artery representsis the proximal portion of this vessel. Further, blood in the PCA begins to flow from the main (basilar) vessel, which provides blood flow. As the brain develops in children, the posterior communicating artery becomes one of the most significant "bridges" between the two vascular beds.
According to statistics, up to 30% of people have the type of structure of the ZMA, 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, the PCA departs from the asymmetrically placed, curved shape of the basilar artery.
About 10% of the world's population have bilateral changes, when two PCA depart from the internal carotid arteries. In these cases well developed back connecting vessels are defined. And the basilar artery is shorter than other people's.
Symptoms of circulatory disorders in PCA
Clinical manifestations of impaired blood flow in the PCA 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. Consequently, the clinic progresses slowly, for a long time there are no symptoms at all.
The most specific disorder of blood flow in the posteriorcerebral artery is an ischemic stroke. This is a disease in which a vessel is clogged with a thrombus or embolus, which prevents blood circulation. As a result, necrosis (death) of a part of the brain occurs.
The following groups of symptoms are distinguished:
- basilar apex syndrome;
- visual disturbances;
- mental disorders;
- motor disorders.
Syndrome of the apex of the basilar artery occurs when blood flow is disturbed in the distal part of the vessel, before it divides into the right and left PCA. In this case, all brain structures that receive blood from the PCA are affected. The patient's consciousness is disturbed up to coma, vision and psyche suffer. Motor function is often preserved.
Features of visual, mental and motor disorders
Visual disturbance occurs when the occipital cortex, optic radiation and geniculate body are damaged. In this case, there is a complete loss of the field of view on the opposite side. For example, if the occipital part of the cortex on the right is affected, a person is not able to see the left half with two eyes. The right visual field remains unaffected. Sometimes not 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. There are visual hallucinations, the patient does not recognize familiar faces, colors. A rare pathology in circulatory disorders in the posterior cerebral artery is Anton's syndrome. When this condition is present, the person does not realize that they are completely blind.
Psychological disorders occur when the corpus callosum and occipital lobe are damaged. A person is not able to read, while the ability to write is preserved. If a person is right-handed, such changes are possible if there is a violation of blood circulation in the left PCA. When a large area of the cortex is damaged, amnesia and psychiatric disorders (delirium) occur. If extensive necrosis of the thalamus occurs, the patient may develop Dejerine-Roussy 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 localization of the lesion in the thalamus;
- lack of movement on the opposite half of the body;
- involuntary spontaneous movements in limbs;
- sense of goosebumps, crawling flies on the skin on half of the body.
Motor disorders in the form of weakness of the upper and lower limbs on the one hand are observed in 25% of patients. This symptom is called hemiparesis, and occurs on the side opposite to the localization of the blockage.
Most often, the cause of motor disorders is a violation of the blood supply to the legs of the brain. However, it is possible to develop paresis 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, a stroke in the vertebrobasilar pool mimics blockage of the vessels of the carotid sinus pool. Sometimes they are difficult to distinguish from each other due to the patient's speech disorders, sensory and motor disorders. Therefore, whenFor the diagnosis of blood flow disorders in the posterior cerebral artery, it is so important to use additional examination methods.
Instrumental diagnosis of stroke in PCA
One of the methods of additional examination when diagnosing a stroke is computed tomography (CT). This is an X-ray method, the essence of which is the layer-by-layer 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 first hours. The radiologist can see a high intensity signal in the picture, 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. They also evaluate options for the anatomy of the posterior cerebral artery, its relationship to the surrounding brain tissue, and the development of collaterals.
But the most informative method for diagnosing circulatory disorders is magnetic resonance imaging. This method does not involve 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 disorders of blood flow in the vessels of the brain depends on several factors:
- acute process (acute, subacute or chronic);
- type of circulatory disorder (ischemic or hemorrhagic);
- presence of concomitant diseases (atherosclerosis, diabetes, arterial hypertension, etc.).
All vascular drugs to improve blood circulation in the brain can be divided into several groups:
- vasodilators 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 for extremely high blood pressure figures. A sharp decrease in pressure is contraindicated, as it can further aggravate the patient's condition.
Calcium antagonist drugs are widely used for vasodilatation. They cause relaxation of the vessel wall and an increase in its diameter.lumen. There are two generations of drugs. The first includes "Verapamil", "Nifedipin", "Dilakor". Second generation: Felodipine, Klintiazem, Nasoldipin.
Antiaggregants and anticoagulants are prescribed for the treatment and prevention of acute disorders of cerebral circulation. They are not able to dissolve an existing blood clot, but prevent the formation of new ones. In modern neurology, thrombolytic therapy is becoming increasingly popular. The use of drugs in this group is more effective, as they can dissolve existing blood clots. Due to the high cost, these medicines are still not available in some hospitals.
The most common antiplatelet agents are:
- "Acetylsalicylic acid";
- "Curantil";
- "Akuprin";
- "Ticlopidine";
- "Aspilat".
The following anticoagulants are most often used in medical practice:
- "Heparin";
- "Warfarin";
- "Clexane";
- "Fragmin".
Nootropics - another group of vascular drugs to improve blood circulation in the brain. These drugs improve the metabolism in its cells, increase their resistance to oxygen deficiency. With the constant use of tablets, memory improves, fatigue disappears, and cognitive functions increase.
The most effective nootropics are:
- "Piracetam";
- "Phenibut";
- "Pantogam";
- "Phenotropil";
- "Cerebrolysin";
- "Glycine".
To improve blood circulation in the brain, herbal medicines are actively used. Preparations based on Ginkgo Biloba are considered especially effective. They reduce tissue swelling, dilate cerebral vessels, increase the elasticity of their walls. Being strong antioxidants, these agents reduce the negative impact of free radicals on brain tissue. The effect of Ginkgo Biloba develops slowly and gradually, so the crus should last at least three months.
Results
The posterior cerebral artery and its branches supply virtually the entire back of the brain. The cortex and underlying structures receive blood from its pool: thalmus, midbrain, internal capsule, corpus callosum, and others. It is thanks to the normal blood flow in these vessels that we can see, move, and think. Therefore, it is so important to know the symptoms of impaired blood flow in the posterior cerebral artery. Timely seeking medical help will allow you to prescribe effective treatment as soon as possible.
Time plays an extremely important role in acute circulatory disorders of the brain. Early therapy increases the chances of a successful rehabilitation of the patient.
