 Ischaemic stroke
In this, the most common type of stroke, the artery is blocked by a blood clot, which interrupts the brain's blood supply.
This
may be due to a cerebral thrombosis (sometimes called a thrombotic
stroke), where a blood clot forms in one of the main arteries leading
to the brain, or to a cerebral embolism (sometimes called an embolic
stroke)...
, in which a blood clot forms elsewhere in the body and is swept into the arteries serving the brain.
Fatty tissue or air bubbles may also form emboli which cause stroke, especially after major trauma.
Another
type of thrombotic ischaemic stroke is called a lacunar stroke. In this
form, one of the tiny blood vessels deep inside the brain tissue
becomes blocked, leading to the death of the small area of tissue that
it supplies. Lacunar strokes are usually less severe.
Haemorrhagic stroke
In
this type of stroke, a blood vessel in or around the brain ruptures
causing bleeding, or a haemorrhage. The build-up of blood presses on
the brain, damaging its delicate tissue. Meanwhile, other brain cells
in the area are starved of blood and damaged.
In an intracerebral
haemorrhage, the bleeding occurs inside the brain itself. In a
subarachnoid haemorrage, the burst blood vessel bleeds into the
subarachnoid space surrounding the brain.
Transient ischaemic attack (TIA)
A
transient ischaemic attack, often known as a mini-stroke, is a brief
episode where some brain function is temporarily lost because of a
short-lived disruption of the blood supply.
Symptoms, such as
weakness of a limb, last for just minutes (typically two to 15 minutes)
before the blood supply returns and everything returns to normal,
because the brain cells haven't suffered permanent damage.
Traditionally
it has been said that if symptoms last less than 24 hours it's a TIA,
but when symptoms persist for more than 24 hours then a stroke has
occurred. But with more powerful and sophisticated brain-scanning
techniques, it has become possible to show that permanent damage (the
real hallmark of a stroke) can usually be detected when symptoms last
more than an hour or so.
TIAs are an important warning sign
that all is not well with the blood supply to the brain. The risk of
suffering a complete stroke within the first month after a TIA may be
as high as 20 per cent, with the risk being even greater in the first
few days following a TIA.
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