Strokes explained

Brain cells die when they no longer receive oxygen and nutrients from the blood, but they are also damaged by sudden bleeding into or around the brain. When blood flow to the brain is interrupted, some brain cells die immediately, while others remain at risk of dying. That's why immediate treatment is critical.

Haemorrhagic stroke accounts for nearly 15 per cent of all strokes and is more frequent among the young and people with high blood pressure. One common cause is a bleeding aneurysm (weak or thin spot on an artery wall). Over time, these weak spots stretch or balloon out under high arterial pressure. The thin walls of these ballooning aneurysms can rupture and spill blood into the space surrounding brain cells.

Haemorrhage can also occur when arterial walls break open. Plaque-encrusted artery walls eventually lose their elasticity and become brittle, thin and prone to cracking. High blood pressure increases the risk that a brittle wall will give way.

When an artery in the brain bursts, blood spews into the surrounding tissue. Brain neurones generally don't come into direct contact with blood; the contact upsets the blood supply and the delicate chemical balance neurones require to function.