What causes stroke?
In 85% of cases, a stroke is caused by a blood clot blocking a cerebral artery, stopping the flow of blood. This is known as ischaemic stroke. The main cause is an accumulation of cholesterol deposits on the walls of the vessels, which narrows the diameter of the artery and encourages its obstruction. This narrowing, known as atherosclerosis, is sometimes localised in the brain, but it can also happen that a fragment of a cholesterol deposit present outside the brain breaks off and migrates via the bloodstream into a cerebral artery.
In 15% of cases, stroke is said to be haemorrhagic, i.e. caused by the rupture of a cerebral artery weakened by high blood pressure (the main cause), a malformation or treatment. The rupture of the artery causes bleeding in the brain.
In an ischaemic stroke, the cells, and in particular the neurons, in the affected region of the brain are hypoxic, i.e. they no longer receive sufficient oxygen and sugar, which are essential for their survival, and which are normally supplied by the bloodstream.
When this situation is prolonged, the cells die, leading to the loss of cerebral functions associated with the affected regions. Initially, cell death occurs only in a small area close to the obstruction. Around this perimeter, there is a “penumbra zone” where the damage caused is reversible if blood circulation is restored quickly, i.e. less than 6 hours after the first signs of stroke.
Blocked circulation in a cerebral artery leads to the death of 1.9 million neurons every minute (total number of neurons: around 100 billion).