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Carotid Disease
The word carotid literally means "to stupefy" which is not surprising when one considers that pressure applied over them renders the victim rapidly unconscious. The carotid arteries reside in the neck. On the right, the common carotid artery arises as a branch of the brachiocephalic artery which comes off the arch of the aorta in the chest.
On the left, the common carotid artery arises directly from the aortic arch. The common carotid arteries divide at the level of the angle of the jaw into external and internal carotid arteries. The external carotid artery divides into several branches supplying the tissues of the face, scalp, mouth, tongue, larynx and pharynx. 

The internal carotid has no branches outside the skull and is responsible for a great deal of the blood supply to the brain. This carotid bifurcation is a very common area for atheroma to collect and it is believed that this is so because there are abnormal shear stresses at this point which has something to do with the fact that the internal carotid artery leads to a relatively low pressure vascular tree compared to that supplied by the external.

      The atheromatous disease leads to the build up of plaque, narrowing of the artery and thus a reduced delivery. Fortunately, the brain is richly supplied not only by the carotid arteries but by two other important vessels called the vertebral arteries. They are responsible primarily for taking blood to the brain stem and cerebellum. The four vessels eventually contribute to a circle of arteries called the Circle of Willis at the base of the brain. 
Provided that the circle is intact, a severe blockage or total occlusion of the one of the carotid arteries can be compensated for. There are also collateral pathways to the brain via terminal branches of the external carotid artery that enter the skull via the eye sockets and nasal passages.
            

WHY DOES CAROTID ATHEROMA MATTER?

It is not uncommon as an incidental findings to discover someone with a completely blocked internal carotid artery on one side. These people are usually without symptoms and there is no indication to do anything about it. Therefore, narrowing or blockage of the carotid arteries per se is not the primary concern. However, the lumps of atheroma have roughened surfaces which produce high, turbulent flow which in turn, can damage the intimal lining and become ulcerated. 

 

Platelets, fibrin and bits of clot tend to stick to these ulcerated areas. The loose friable fragments then become detached by the turbulent blood rushing past and are then carried up into the cerebral vascular tree leading to a stroke. The resulting stroke can be extensive, life-threatening and permanent or minor and temporary depending upon the size of the particle and the area of brain tissue affected. 

The temporary strokes are called Transient Ischaemic Attacks or TIAs. These events can be very frightening for the person concerned who is at great risk of going on to develop a permanent stroke if not correctly managed.

Treatment of transient ischaemic attacks (TIA's)

It is estimated that TIAs are caused by extracranial carotid disease in 20 - 50 % of cases. Treatment can be medical or surgical and is dependent upon the extent of the disease, its severity and other unrelated factors such as general health and fitness to undergo anaesthesia. 

Using Duplex Doppler scans it is possible to obtain a quick and non-invasive assessment of the carotid arteries  Most specialists are agreed that a narrowing of the internal carotid artery of 70% or more in a patient having TIAs, should undergo surgery to remove the offending plaque providing they are fit enough to do so.
      

There have been large studies carried out in America and  in Europe which came to the same conclusion about this point. However, the studies which involved thousands of patients, were not directly comparable because the method of measuring the percentage narrowing in the artery was different leading to considerable discrepancy between the study populations. 

 
One of the studies tended to overestimate the narrow segment in percentage terms because the point of reference was different. This has led to controversy and lengthy debate about who should and who should not receive surgical treatment. Furthermore, it is still unclear what to do about the patient with a severe narrowing of the artery (70-99%) who is nevertheless without symptoms. It is well-known that it is possible to live perfectly happily with a completely blocked internal carotid artery on one side. They have clearly resulted from the ultimate conclusion of the atheroma; namely final thrombosis of the artery when the flow becomes so slowed by the narrowed segment that clotting occurs. It can therefore be argued, that since it is not known how many people occlude their carotid arteries and of those that do, what percentage are rendered disabled by stroke, more knowledge of  the natural history of the disease is required before jumping to conclusions about its significance. 
Carotid endarterectomy is a procedure with low but nevertheless devastating risks and is therefore not to be undertaken lightly. There is universal agreement that people with a less than that 70 per cent of stenosis who have no symptoms are best treated by medical means usually with a small dose of aspirin or another anti-platelet agent plus any other therapy to control things like hypertension etc. The evidence for surgery in this group is not persuasive and indeed there is a suggestion that these people may actually be done positive harm. In the case of severe disease the evidence would appear to be to the contrary although the issue of symptoms versus no symptoms still needs to be worked out. This is the subject of an ongoing trial in the UK the results of which are not expected for some time.