There are two main ways an ischaemic stroke can happen (stroke caused by a blockage in an artery):
A blood clot can form somewhere in the body and travel to the brain. This is an embolus.
A clot can form directly in a blood vessel in the brain and remain there, causing a blockage. This is a thrombosis.
There are several different risk factors for ischaemic stroke in children. These fall mainly into the following categories:
Heart disorders cause up to 25 per cent of ischaemic strokes in children. They can be a result of congenital heart disease (CHD) an abnormality present since birth or acquired heart disease (AHD). They commonly occur around the time of operations on the heart. Most children with a heart disorder have this diagnosed before their stroke. For some, the problem is only discovered after a stroke has happened.
Blood disorders, like sickle cell disease (SCD), are another risk factor for childhood ischaemic stroke. SCD is an inherited condition, which affects the development of red blood cells. They change from their normal round shape to a sickle (half moon) shape. Because sickle cells are less flexible, they can get stuck in blood vessels and block them. SCD can cause strokes if a vessel in the brain becomes blocked. In rare circumstances, it can cause bleeds in the brain.
SCD is most common among Black Caribbean, Black African and Black British people. It affects both males and females alike. Children with SCD are at the greatest risk of stroke between the ages of 2 and 16. (To find out more about sickle cell disease read our leaflet Sickle cell and stroke.)
There are several types of blood clotting disorders, which are risk factors for ischaemic strokes in children. Sometimes referred to as sticky blood disorders there is an increased tendency for clots to form. The doctor may take blood samples to see if your child has one of these disorders if they have had a stroke.
Infections have also been associated with ischaemic stroke. Chicken pox is a highly contagious condition, which mainly affects children under the age of ten. It is caused by a virus. Usually the virus runs its course but research has shown that it can be a risk factor for ischaemic stroke in children, though this is rare. It is thought that the virus causes blood vessels in the head to narrow. Research suggests that children with underlying cardiac and vascular conditions, who become infected with the virus, may be at a higher risk of stroke.
Other infectious disorders that have been associated with childhood ischaemic stroke are bacterial meningitis, encephalitis, sepsis and brain abscess.
Vascular disorders are problems with vessels in the body. Furring up of arteries are a common cause of stroke in adults but vessel problems can also cause stroke in children. In children they occur for very different reasons however, due to rare conditions such as arterial dissection, moyamoya syndrome and vasculitis.
An arterial dissection is a tear in the lining of an artery. It occurs when blood gets between the layers of the blood vessel wall. This can cause blood to escape from the vessel into the brain, or to form a blood clot in the artery causing a stroke. Recent studies have shown that carotid and vertebral artery dissection (damage to the arteries in our necks) accounts for five to 20 per cent of strokes in children. Common symptoms (of arterial dissection) are sudden and severe headache, face and neck pain followed by stroke like symptoms. These types of stroke are more common in males. Often the cause of the dissection is a trauma to the neck.
Moyamoya disease affects one in every million people in the UK. It is a rare disease, associated with narrowing and blockages in the main blood vessels in the brain. In children symptoms are recurrent headaches, weakness on one side of the body, seizures and learning difficulties. Moyamoya disease has been reported in all ethnic groups but mainly in Japanese people. Researchers believe that it is a genetic condition, though more evidenceis needed to support this theory. It has also been linked with SCD.
There is also evidence of vasculitis causing stroke or TIA in children. Vasculitis means inflammation of the blood vessels. It can affect any vessel in the body and can cause narrowing and vessel wall weakness. A stroke can happen if a blood clot blocks an affected vessel in the brain or if the vessel wall bursts and causes a bleed into the brain.
Strokes can also be caused by a problem with the veins of the brain. Veins bring deoxygenated blood (without oxygen) back to the heart.
Sinovenous thrombosis is a disorder that affects a vein in the brain. It occurs when a blood clot develops in the large veins (known as the venous sinuses) that bring blood from the brain back to the heart. Symptoms include headaches, fits and raised pressure in the brain. This can affect all ages but is under recognised in babies under twenty-eight days old. Common risk factors are infections in the head and neck (such as an ear or sinus infection), dehydration or blood clotting disorders.