A narrowed carotid artery is usually discovered in one of two ways. Either you have had a warning event, a TIA, a minor stroke or a brief loss of vision in one eye, and a scan of the neck arteries was part of the work-up. Or it was found by chance, on a scan done for something else. The two situations are quite different, and the question of surgery is answered differently for each.
What the carotid arteries do, and what goes wrong
The two carotid arteries run up either side of the neck and supply the front two-thirds of the brain and the eyes. Like any artery they can develop atherosclerotic plaque, most often at the point where the artery divides just below the angle of the jaw. The problem is rarely that the narrowing starves the brain of blood. The brain has other supply routes. The problem is that plaque can become irregular, clot can form on its surface, and small fragments can break off and lodge in a brain artery. That is what causes a TIA or stroke.
The NHS estimates that about a quarter of strokes in the UK are caused by narrowing of the carotid arteries, which is why they are routinely scanned after a TIA.
A TIA is a warning, and the clock is running
A transient ischaemic attack produces the same symptoms as a stroke, typically weakness or numbness of the face, arm or leg on one side, slurred or muddled speech, or loss of vision in one eye, but they resolve, usually within minutes and always within 24 hours. Because the symptoms go away, people are tempted to wait and see. That is the wrong instinct. The risk of a full stroke is highest in the days and weeks immediately after a TIA. NICE guidance is that anyone with a suspected TIA should be assessed by a specialist within 24 hours and started on aspirin immediately unless there is a reason not to.
If the carotid scan then shows a significant narrowing on the side that matches the symptoms, surgery is time-critical. The large randomised trials that established carotid endarterectomy showed that the benefit is greatest when the operation is done within two weeks of the event and falls rapidly thereafter. UK national pathways aim for surgery within 14 days of symptoms, and the Get It Right First Time programme recommends 7.
How the narrowing is measured
The first test is a carotid duplex ultrasound, which measures blood flow velocity through the narrowing and estimates its severity as a percentage. Good practice is to confirm the degree of narrowing with a second scan by a different operator, or with a CT or MR angiogram, before surgery.
The percentage depends on how it is measured. The two conventions, called NASCET and ECST after the trials that used them, give different numbers for the same artery, and a 50% NASCET stenosis is roughly a 70% ECST stenosis. Any report should say which was used; if yours does not, ask. The thresholds below use NASCET, as NICE does.
Who benefits from surgery
Symptomatic narrowing of 50% to 99%
NICE recommends that people with stable symptoms from a TIA or non-disabling stroke and a carotid narrowing of 50% to 99% (NASCET) are assessed and referred urgently for carotid endarterectomy, alongside best medical treatment. The evidence behind this is a pooled analysis of the major trials, summarised by Cochrane: for narrowings of 70% to 99% surgery reduced the absolute risk of stroke by about 16 percentage points over five years, and for 50% to 69% by about 4.6 points. The benefit was greatest in men, in people over 75, and in those operated on within two weeks.
Symptomatic narrowing below 50%
Here the trials showed no benefit from surgery, and NICE is explicit that these patients should not be operated on. The treatment is medical: an antiplatelet, a high-intensity statin, blood pressure control and stopping smoking.
Narrowing with no symptoms
A narrowing found by chance, which has never caused a TIA or stroke, carries a lower risk, typically quoted at around 1% to 2% per year, and modern medical treatment has lowered it further. Older trials showed a small benefit from operating on asymptomatic narrowings of 60% or more, but with today's drugs the margin is narrower and surgery for asymptomatic disease has become much less common in the UK. It can still be the right choice for some people, particularly younger patients with a tight narrowing and features of plaque instability on imaging, and that is a conversation to have with a vascular surgeon rather than a rule.
Near-occlusion and complete blockage
Counter-intuitively, an artery that is almost or completely blocked is usually not operated on. The trials found no benefit for near-occlusion, and a fully blocked carotid cannot be reopened safely. Treatment is medical and the attention shifts to the other side.
What the operation involves
Carotid endarterectomy is done through an incision down the side of the neck. The artery is clamped, opened, the plaque is peeled out and the artery is closed, often with a small patch to widen it. It takes one to two hours and can be done under local anaesthetic with you awake, which lets the team monitor your brain function directly, or under a general anaesthetic. Most people stay one or two nights and are back to normal activities within a few weeks.
The main risk is a stroke during or shortly after surgery, which affects between 1 and 3 people in 100 in UK practice. There are smaller risks of heart attack, bleeding, wound infection and bruising of the nerves near the artery, which can temporarily affect the voice, the tongue or swallowing. These risks are the reason the thresholds above exist: surgery is offered when the risk of stroke without it clearly exceeds the risk of the operation. Every UK carotid operation is submitted to the National Vascular Registry, which publishes outcomes by unit.
Carotid stenting, a keyhole alternative delivered through the groin, has a place for people whose neck is unsuitable for surgery, for example after radiotherapy or previous neck operations, or where the narrowing is too high to reach. For most patients the trials favour endarterectomy, mainly because of a lower procedural stroke rate.
Medication is not optional
Whether or not you have surgery, best medical treatment is what protects you long term: an antiplatelet (clopidogrel or aspirin), a statin, blood pressure control, treatment of diabetes and stopping smoking. Surgery removes one plaque. Medication slows the disease everywhere else.
Driving
After a TIA or stroke you must not drive a car or motorcycle for at least one month, and you may only restart if your recovery is satisfactory. The rules are stricter for bus and lorry licences. GOV.UK sets them out and your clinician will advise.
What happens at a private consultation
Most people with a symptomatic narrowing are already in the NHS TIA pathway, and the right thing is to stay in it; it is built for speed. Where I most often see people privately is with an asymptomatic narrowing found by chance, with a scan report they do not understand, or when they want a second opinion before deciding. The appointment covers your history and risk factors, a review of your imaging, a repeat duplex scan where that would change the decision, and a plain explanation of where you sit against the thresholds above and what I would advise. You leave with a written plan and a letter to your GP.
Frequently asked questions
What is carotid artery stenosis?
A narrowing of one of the two carotid arteries in the neck that supply the front of the brain, caused by a build-up of fatty plaque (atherosclerosis). The danger is not the narrowing itself but fragments of plaque or clot breaking off and travelling to the brain, causing a TIA or stroke.
Does a narrowed carotid artery always need surgery?
No. Surgery is recommended when the artery has recently caused symptoms (a TIA, a minor stroke or temporary loss of vision in one eye) and the narrowing is 50% to 99% on NASCET criteria. Narrowings below 50% are treated with medication, not surgery. Narrowings that have never caused symptoms are a separate discussion and are operated on much less often in the UK.
Why is timing so important after a TIA?
The risk of a full stroke is highest in the first days and weeks after a TIA, and the benefit of carotid endarterectomy falls quickly the longer surgery is delayed. UK standards aim for surgery within 14 days of symptoms, and ideally within 7.
What does carotid endarterectomy involve?
An operation through an incision in the side of the neck, under local or general anaesthetic, in which the artery is opened and the plaque removed. Most people stay one or two nights in hospital.
What are the risks of carotid surgery?
The main risk is stroke during or soon after the operation, which affects between 1 and 3 people in 100 in UK series. There are smaller risks of heart attack, bleeding, wound infection and temporary nerve bruising affecting the voice, tongue or swallowing. For the right patient the risk without surgery is considerably higher.
Can I drive after a TIA?
Car and motorcycle licence holders must stop driving for at least one month after a TIA and may restart only if there has been a satisfactory recovery. The DVLA rules are published on GOV.UK and are stricter for bus and lorry licences.
Told you have a narrowed carotid artery?
Mr Neville Dastur is a consultant vascular and endovascular surgeon who performs carotid endarterectomy at Frimley Health. Private arterial clinics at Frimley Park.
This article is for general information only and is not a substitute for personalised medical advice. Treatment suitability depends on individual assessment.