In detail

Vascular pathologies of the brain: ischemic and hemorrhagic stroke

Vascular pathologies of the brain: ischemic and hemorrhagic stroke

A cerebral vascular accident or CVA is a neurological pathology in which an poor blood flow in the brain, causing cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, consequence of bleeding. The result is that part of the brain does not work properly.

Cerebral AVC is one of the most frequent neurological pathologies; after heart problems and cancers, it is the third cause of death.

Content

  • 1 Vascular territories
  • 2 Types of cerebral vascular accidents (AVC)
  • 3 Zone of ischemic penumbra and edema

Vascular territories

A vascular territory is an area irrigated by one of the arteries that we have commented previously. Each artery has a vascular territory, that is, it irrigates a certain area. In total, we have six arteries, three for each hemisphere: two later (of the vertebral system), two previous and two socks (of the carotid system). Therefore, there are three vascular territories:

Anterior Cerebral Artery (ACA): It originates with the internal carotid artery, which at the base of the brain is divided into different branches, among which the middle cerebral artery and the anterior cerebral artery should be highlighted. Irrigate the medial part of the frontal lobe, the medial part of the parietal and two thirds of the corpus callosum. In addition, it enters two subcortical structures, the caudate nucleus and the anterior arm of the internal capsule.

Middle Cerebral Artery (ACM): Irrigate the basal ganglia (putamen, Pale Balloon and part of the caudate nucleus), the posterior arm of the internal capsule and the lateral surface of the frontal, parietal and temporal lobes. It is the artery that irrigates more territories.

Posterior Cerebral Artery (ACP): It originates with the two vertebral arteries, which at the level of the protuberance join to form the basilar artery. This is divided into the different arteries that supply the cerebellum and the posterior cerebral arteries. Irrigate the medial and basal part of the temporal lobe (hippocampus), the occipital lobe, the splenus of the corpus callosum and the thalamus.

Border areas

There are border areas that are located between different vascular territories, areas that can be joined in two vascular territories. When there is a lack of oxygen (anoxia), the area that is affected before is the peripheral, since it is where the blood comes last. Thus, they are more sensitive to the lack of oxygen since they are the first to run out (unlike the central zone).

The affectation of the different vascular territories will produce one symptomatology or another.

Representation of the vascular territories of the anterior cerebral, middle cerebral and posterior cerebral arteries.

Types of cerebral vascular accidents (AVC)

When a AVC in some vascular territory, it stops receiving oxygen and glucose transported by blood. After a few minutes without normal blood flow, the brain tissue is irreversibly damaged, and we say that an area of ​​infarction has occurred.

We can divide the AVC into two large groups, the ischemic and hemorrhagic.

Ischemic AVC

The majority of accidents are of this type (it represents 80% of the total of the AVC). They occur when a fatty substance called atheroma plaque builds up in the arteries and narrows causing an occlusion of a blood vessel, causing anoxia or hypoxia and, consequently, necrosis of the nervous tissue, which is infarcted.

Types of ischemic stroke

There are three main types of ischemic stroke:

  • Thrombotic infarctions. They are caused by a blood clot that forms in an artery that supplies blood to the brain.
  • Embolic infarctions. They happen when a clot forms somewhere else in the body and travels through the blood vessels to the brain. It gets stuck there and stops the flow of your blood.
  • Hemodynamic infarctions they are due to reductions in blood flow, for example, due to cardiac arrest. These infarctions especially affect areas of the brain irrigated by the most distal parts of the arteries (bordering territories).

The most frequent are arterial thrombi, which are a consequence of the formation of lipid plaques in the walls of the arteries. These plaques can develop to cause a complete occlusion of the lumen of the blood vessel, in a process that can last from twenty to thirty years.

The embolic infarctions they can occur by breaking a atheroma plate (accumulation of cholesterol in the wall of an artery). The fragment that emerges travels through the bloodstream until it reaches an artery of smaller size, blocking it. In most cases, these are emboli originating in the heart (cardioembolic AVC). In this case, due to dysfunctions in the heartbeat, emboli are formed that travel up to clog a cerebral artery.

Image obtained by CT where you can see a cerebral infarction (hypodense area) that affects the cortex of the right hemisphere of the brain.

Symptoms of ischemic stroke

The symptoms of an ischemic stroke depend on where in the brain it is affected. They can include:

  • Sudden numbness or weakness of the oyster, arm or leg, often on one side of the body.
  • Confusion.
  • Trouble speaking or understanding others.
  • Dizziness, loss of balance or coordination or difficulty walking.
  • Loss of vision or double vision.

Someone is more likely to have an ischemic stroke if:

  • Is over 60 years old
  • You have high blood pressure, heart disease, high cholesterol or diabetes
  • Have irregular heartbeats (arrhythmias)
  • Smoke
  • Have a family history of strokes

Transient Ischemic Accidents (AIT)

TIAs are temporary occlusions of an artery

These are micro-symbols that obstruct the circulation for a maximum of twenty-four hours, although generally, the symptomatology, similar to that of ischemic HCVs but of less intensity, resolves in minutes. A high percentage of these patients are at risk of suffering an ischemic stroke if the cause of their vascular problems is not treated.

Hemorrhagic stroke

20% of AVCs are hemorrhagic. They are produced by the rupture of an artery, and the subsequent extravasation of blood. Hemorrhagic stroke is caused by bleeding directly into the brain parenchyma. The usual mechanism is believed to be a leak of small intracerebral arteries damaged by the chronic hypertension.

Patients with intracerebral hemorrhages are more likely than those with ischemic stroke to have a headache, altered mental status, seizures, nausea and vomiting and / or marked hypertension. Even so, none of these findings reliably distinguishes between a hemorrhagic or an ischemic AVC.

Types of hemorrhagic stroke

Hemorrhages are usually defined depending on their location: epidural, subdural, subarachnoid, intracerebral (or intraparenchymal) and intraventricular.

The epidural and subdural hemorrhages they are often of traumatic cause, which causes the rupture of meningeal arteries with the consequent accumulation of blood in the epidural or subdural spaces. This blood compresses the brain tissue and causes focal symptomatology, coma and death by understanding the structures of the brain stem.

An important complication that is usually observed in subarachnoid hemorrhages is the vasospasm. For reasons not well known, but possibly related to the accumulation of extravased blood, some arteries can spasm and contract, so that blood circulation will be interrupted and infarctions will occur in the vascular territories irrigated by these arteries.

Subarachnoid hemorrhage It can be of traumatic cause or due to the rupture of an aneurysm. Aneurysms are sac-shaped dilatations of the walls of the arteries, usually congenital, that can rupture and extravacate the blood content in the subarachnoid space.

Images obtained by CT where two different subarachnoid hemorrhages are observed.

Intracerebral hemorrhage It is related to high blood pressure. Chronic hypertension weakens the walls of blood vessels and at some point pressure rise some vessel can be broken and extravasated in the blood to brain tissue. This, in turn, will cause other smaller vessels to rupture, and increase the size of the lesion.

Image showing the accumulation of blood in the left brain tissue as a result of hemorrhage.

Another cause of intracerebral hemorrhage is the rupture of arteriovenous malformations (AVM). AVMs are areas of abnormal communication between the arterial and venous systems that have an abnormal flow of circulation. Although it is a developmental anomaly, they are not usually symptomatic until they are twenty or thirty years old, when they can rupture and cause cerebral hemorrhage or epileptic seizures due to irritation of nearby neuronal tissue.

In some cases, brain hemorrhages may open to the ventricular system. Intraventricular hemorrhages complicate the patient's prognosis, as they can often cause hydrocephalus (Abnormal increase in the amount of cerebrospinal fluid in the brain's cavities).

Symptoms of hemorrhagic stroke

The type of deficit depends on the area of ​​the brain involved. If the dominant hemisphere (usually the left) is involved, the following symptoms may occur:

  • Right hemiparesis
  • Loss of the right hemisphere
  • Left Look Preference
  • Right field of view cut
  • Aphasia
  • Forgotten (atypical)

If the non-dominant hemisphere (usually the right one) is involved, the following symptoms may occur:

  • Left hemiparesis
  • Loss of the left hemisphere
  • Preference of the right look
  • Left field of view cut

Zone of ischemic penumbra and edema

The obstruction of a blood vessel causes intense ischemia in the center of the vascular territory and less intense ischemia in the periphery. Ischemic nucleus cells die quickly, and neurological involvement is irreversible.

The periphery cells see their functional activity altered, but retain their structural integrity for a certain time. This area has been called ischemic penumbra.

Neurological symptoms due to the involvement of the cells of the ischemic penumbra zone are reversible.

When a vascular territory is infarcted, irreversible cell damage occurs. The functional alteration of the ischemic penumbra zone, on the other hand, is reversible.

Therefore, it must be achieved restore normal blood flow as quickly as possible and minimize the effects of energy depletion and edema.

The term edema refers to the accumulation of fluid in the tissue. This fluid can accumulate inside the cells (cytotoxic edema) or in the extracellular space (vasogenic edema).

The presence of edema displaces and compresses adjacent brain structures, which increases functional impairment and makes it difficult to recover areas of ischemic penumbra.

References

Carpenter, M.B. (1994). Neuroanatomy Fundamentals Buenos Aires: Panamerican Editorial.

Delgado, J.M .; Ferrús, A .; Mora, F .; Blonde, F.J. (eds) (1998). Neuroscience Manual. Madrid: Synthesis.

Diamond, M.C .; Scheibel, A.B. and Elson, L.M. (nineteen ninety six). The human brain Work book. Barcelona: Ariel.

Guyton, A.C. (1994) Anatomy and physiology of the nervous system. Basic Neuroscience Madrid: Pan American Medical Editorial.

Martin, J.H. (1998) Neuroanatomy. Madrid: Prentice Hall.

Nolte, J. (1994) The human brain: introduction to functional anatomy. Madrid: Mosby-Doyma.

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