A stroke occurs when a part of the brain is damaged. This happens for two main reasons. Firstly, bleeding can occur into the brain and damage the brain tissue. This is called a haemorrhagic stroke. About 20% (1 in 5) of all strokes are haemorrhagic strokes. Secondly and more commonly, the arteries which take blood to the brain can become blocked. This called an ischaemic stroke. About 4 out of every 5 strokes are ischaemic strokes.
If a major artery to the brain is blocked, part of the brain tissue can die from lack of oxygen carried in the blood. When brain tissue dies the effects on the body will depend on what functions of the body that part of the brain controls. The effects on the body are commonly referred to as a stroke. For instance paralysis of the right side of the body (right sided stroke) will be due to damage to the left half of the brain. Inability to speak will also be due to damage to the left side of the brain in most patients, because it is the left side of the brain that controls speech. The severity of the stroke can vary enormously depending on how much of the brain is damaged.
Even if the main internal carotid artery blocks on one side of the neck the risk of stroke is only about 10-15% (1 in 10 to 1 in 7). This is because there is frequently enough blood reaching the brain from the opposite side and also from other arteries supplying the back of the brain (vertebral arteries).
Each year about 7600 New Zealanders suffer a stroke. The FAST campaign (see left) aims to improve the recognition of stroke and its subsequent timely and rapid management. Although the FAST check does not mention leg symptoms they are of the same importance as weakness in the arms.
TIA stands for Transient Ischaemic Attack. This is sometimes known as a ministroke. A TIA is a stroke that lasts for less than 24 hours, and full recovery occurs. Patients will experience the symptoms of a stroke, but then they will fully recover often within 2 or 3 hours. This is because the damage to the brain tissue is temporary and reversible. TIAs can affect the body in exactly the same way as a stroke, but in a TIA, the patient makes a complete recovery within 24 hours.
Dizzines and giddiness, blurred vision and unsteadiness are not typical symptoms of a TIA or a stroke on their own. This important as these patients with these symptoms are unlikely to benefit from treatment of the carotid arteries in the neck.
TIAs are important because they can be a warning that a more severe stroke may take place. In some patients with TIAs there will be a narrowing in a major blood vessel to the brain. This blood vessel is called the internal carotid artery and there are two of them - one on each side of the neck. When this artery becomes diseased, it frequently becomes narrowed and lined by fragile material. This fragile material can break off into fragments and travel up to the brain and cause a stroke or TIA, by blocking the blood supply to an area of brain tissue. The fragments can be quite small and may only cause problems to a small area of brain. The area can be so small that the blood supply to other parts of the brain can compensate and a full recovery takes place. If a larger fragment breaks off or the main carotid artery blocks completely then a more severe stroke can occur.
Although all patients with a TIA should have further investigations, the chances of having a stroke after a TIA are greater if the patient is over 60 years old, has high blood pressure (>140 mmHg), temporary paralysis down one side and symptoms for more than one hour (Rothwell et al, 2005). The ABCD2 score shown in the table gives an approximate prediction of risk at 2 days following the first TIA based on the features shown. A score of 0-3 gives a risk of 1%, 4-5 a risk of 4% and a score of 6-7 a risk of 8% for further stroke in the next 2 days.
We now know that if a TIA occurs and the internal carotid artery is severely narrowed then an operation (carotid endarterectomy) to correct the narrowing can prevent further major and minor strokes. Special tests are needed to check the carotid arteries and see if they are narrowed.
It is impossible to tell by a routine clinical examination if your carotid arteries are narrowed. Although abnormal sounds (bruits) can sometimes be heard over the arteries when listening with a stethoscope, this is a very poor indicator of narrowing of the arteries. About 4% (4 in 100) people over the age of 45 years will have a bruit. Only about 20% (1 in 5) of these patients will have a severe carotid narrowing (Aboyans, 2008). However, there is evidence that the presence of a carotid bruit may confer an increased risk of heart attack and cardiovascular death (Pickett, 2008). According to this study this risk of heart attack or cardiovascular death was about twice that of people without a carotid bruit (3.7 with bruit vs 1.9 without bruit per hundred patient years). Still the majority of patients will not suffer a serious event. The implication of the study is that an aggressive approach to treating vascular risk factors should be adopted but this is, as yet, not proven.
The only way to know for certain if the carotid arteries are narrowed is to undergo an ultrasound scan of the arteries. This can be a very accurate test and will discover whether the arteries are normal or whether there is any narrowing present. Many surgeons will offer surgery on the basis of the scan test alone.
You should definitely have a scan of the carotid arteries if you have had a TIA or have had a stroke from which you have made a full or partial recovery. This should be arranged urgently as the risk of further problems is greatest in the early period after the first event. It is important to remember that even in patients who have not made a full recovery from a stroke, surgery may be crucial in preventing further deterioration.
The figure right shows an ultrasound scan of normal carotid arteries at the point where the common carotid artery divides into the external and internal carotid arteries. If you have had no strokes or TIAs the need for a scan is more controversial as the risk of stroke is low (see below). However, if you have disease in arteries in other parts of the body such as the heart or the legs or you have high blood pressure and smoke cigarettes it may be worth considering a scan. In these circumstances there is an increased chance there will be narrowing in the arteries that has not yet caused symptoms. If you are under the age of 75 years you would be more likely to benefit from carotid surgery even if you have not yet had any TIAs or strokes.
Carotid endarterectomy is the operation used to remove the narrowing from the lining of the carotid artery. It may be performed under a general (patient asleep) or a local/regional (patient awake) anaesthetic. Both are used widely and there is no evidence that one is better than the other (see GALA trial). One of the first operations was reported in November 1954 from London (Eastcott HG et al, 1954).
An incision is made in the neck from close to the ear lobe and courses down towards the collar bone in the midline. Some surgeons use an incision across the neck. Both incisions heal well. The arteries are located and prepared. During the operation to remove the diseased lining, the arteries must be clamped. This obstructs the blood flow to the brain and so surgeons frequently insert a plastic tube (shunt) to carry blood to the brain during this part of the operation. The diseased lining to the artery is carefully removed to leave as smooth a surface as possible. Many surgeons then close the artery using a patch to avoid causing further narrowing to the artery. A recent review has shown that closing the artery using a patch (patch angioplasty) lowers the risk of stroke or death not only around the time of the operation but also in the longer term (Bond R et al, 2004).
The most important risk to patients is the risk of further stroke. Because the operation is performed on a diseased artery carrying blood to the brain, there is a risk during the operation or shortly after (particularly the first 24 hours), that a further stroke may occur. This is in fact uncommon and affects about 3% of patients or less. This means that in more than 95 patients out of every 100 no further stroke occurs around the time of the operation. However, it is important to realise that stroke is a real, but small risk of the operation. There is also a smaller risk of death, but this is very low at around 1% or less. This means that 99 out of every 100 people will not die.
There are a number of nerves that run close to the operation site that can be injured. The commonest is a sensory nerve (greater auricular nerve) to the upper part of the neck. Injury to this nerve can lead to some tingling or numbness in the neck and earlobe, but it is not usually a significant problem. The other nerve commonly seen is the hypoglossal nerve. This nerve controls movement of the tongue. It is occasionally injured and leads to deviation of the tongue to one side. Usually these problems are temporary because the nerve is bruised and not actually cut. There is a small risk of the artery renarrowing after surgery. This risk is low at probably less than 2% and rarely leads to symptoms.
The pooled data from the trials provides the firmest evidence of benefit. A total of 6092 patients with 35,000 years of follow up were analysed. Carotid endarterectomy was only helpful in patients with greater than 50% narrowing of the internal carotid artery. The more severe the narrowing the greater the benefit in reducing further strokes. There is no benefit in having an operation once the artery is blocked.
In patients with 50-69% narrowing the risks of stroke or death were reduced by 7-9% at 5 years after surgery. In patients with more severe narrowing greater than 70% the risks of stroke or death were reduced by 14-19% at 5 years after surgery. In certain groups of patients with very narrowed arteries the benefits of surgery can be even greater. The pooled analysis also showed that surgery within 2 weeks of a non-disabling stroke or TIA produced significantly more benefit than surgery at a later date. In a subgroup of patients with a 70% or greater narrowing, surgery within 2 weeks was associated with a 30.2% absolute reduction in the subsequent risk of stroke.
It is important to realise that these reductions in risk for a patient are very great when compared with other medical measures to prevent stroke or death. For instance the use of drugs to lower the cholesterol level only reduces the risk of death by 1-2%. The benefits for carotid endarterectomy are many times greater than taking tablets. Be careful when reading claims regarding reductions in risk particularly for medications used to lower blood pressure and cholesterol.
