02. Stroke

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1. General:

The brain accounts for less than 2% [ 137 ] of the weight of the human body. However, he alone receives more than 16% [ 5 ] of all the blood supply of the latter. It is a member of a very high metabolic activity, it requires more than 20% [ 138 ] of the energy input of the whole body.

Unfortunately, the brain has very low energy reserves (oxygen and glucose) [ 109 ]. Neurons die after a few minutes in the absence of energy intake [ 105 ]. If a neuron dies, there is very little chance that it is replaced. It is for this reason that the maintenance of cerebral vascular supply is of paramount importance.

The stroke [ 4 , 178 ] (stroke or brain attack) is a sudden interruption of blood flow to an area of the brain is complicated by neurological disorders [ 179 ].

Depending on their nature, distinguishes between two entities of stroke: Ischemic stroke, by blockage of a blood vessel (80% of all strokes), and hemorrhagic stroke that causes bleeding in the brain ( 20% of strokes) [ 180 ].

2. Ischemic stroke:

2.1. Causes:

Ischemic stroke [ 69 ] is the result of occlusion of an artery that vascularized the brain (cerebral artery, internal carotid or vertebrobasilar system). This leads to cerebral infarction (cerebral infarction or [ 181 ]).

This obstruction may have several origins:

  • Obstructive atheroma,
  • An isolation of a clot formed locally or cardiac,
  • A tear in the artery wall (dissection)
  • A compression by a tumor ...

2.2. Clinic:

The deficit caused interested cerebral territory well defined: it is said systematized. The clinical manifestations [ 69 ] will depend on the territory reached.

Thus, if the left posterior cerebral artery is reached, the subject will develop a right homonymous hemianopia. If, against what is left is affected middle cerebral artery, the subject will develop a sensorimotor deficit right side of the body most often associated with aphasia.

Ischemic stroke may be transient (transient ischemic attack or TIA [ 31 ]) with rewind, and without sequelae in the normal state. The deficit may be permanent, in the case of stroke made ​​(Made Ischemic Accident or AIC [ 184 ]).

2.3. Pathophysiology [ 183 , 185 ]:

Severe and prolonged interruption of cerebral blood flow even in a small region of the brain causes tissue hypoxia leading to:

  • Metabolic changes (anaerobic glycolysis, lactic acid formation)
  • Excessive release of glutamate, a neurotransmitter that high concentration is toxic to nerve cells [ 41 ],
  • A malfunction pumps Na + / K + [ 86 ] to cause a Ca + + entry in intracellular [ 183 ] ...

All these disturbances causes a cascade of enzymatic activation and accumulation of acid metabolites and cytotoxic free radicals [ 69 ] leading to irreversible cell injury. That is why the initial stroke symptoms may be minor at first, but if not caught early clinical picture may worsen.

Membrane abnormalities and disorders of capillary permeability are complicated by cerebral edema observed in the ischemic zone.

In addition to the direct impact of cerebral hypoperfusion in the ischemic region, these metabolic complications will extend to the neighborhood called the penumbra [ 183 ].

Cerebral ischemic softening may complicate secondary bleeding at the injury: this is called hemorrhagic softening [ 182 ].

3. Hemorrhagic stroke:

The hemorrhagic stroke [ 69 ] is due to the rupture of a blood vessel that is often damaged (arteriovenous malformation or aneurysm [ 38 ]) and subjected to excessive blood pressure. Tobacco and alcohol are factors that undermine the more blood vessels.

In a hemorrhagic stroke, a hematoma forms quickly causing focal neurological signs of acute onset in relation to brain structures destroyed or compressed.

Edema which is worse around the hematoma compressing the brain in the skull and causes or increases intracranial pressure (intracranial hypertension). The skull being inextensible, nerve structures under pressure can s engage in the falx or through the foramen magnum threatening.

Sometimes during a hemorrhagic stroke, there is a massive release of calcium ions, this leads vasospasm [ 69 ] which can be sudden to the other ischemic origin.