The Carotid and Vertebral Arteries; Transcranial Colour Doppler

Cerebral Ischaemic Symptoms

There are many causes of cerebral ischaemic symptoms apart from disease at the carotid bifurcation. These include cardiac arrhythmias, hypotensive episodes, emboli and atheromatous disease elsewhere in the circulation between the heart and the intracerebral arterioles. Many of these can be treated with medical therapy but it is only the extracranial section of the carotid artery which is amenable to surgery, and it is for this reason that so much effort is devoted to the assessment of this area. The main aim is to classify patients into five main groups.

• 1.

  Those without significant disease.

• 2.

  Those with mild disease (< 50% diameter reduction), who will benefit from medical therapy if they are symptomatic.

• 3.

  Those with more severe disease (50–70% diameter stenosis), who will be treated medically and may be followed to assess progression of disease, particularly if they are symptomatic.

• 4.

  Those patients with severe disease (> 70% diameter reduction) who will benefit from surgery if they are symptomatic.

• 5.

  Those patients with a complete occlusion, who are therefore not candidates for surgery.

The relationship between the presence of carotid artery disease and the development of cerebral ischaemic symptoms is not straightforward and detailed discussion of this subject is beyond the scope of this book. However, patients who have suffered from temporary ischaemic symptoms, such as TIA, reversible ischaemic neurological deficits, or amaurosis fugax, are significantly more likely to suffer a stroke than asymptomatic subjects: 36% of patients who have a TIA will have an infarct within 5 years of the TIA, compared with an annual stroke rate of 1% for asymptomatic, elderly individuals. Therefore it is reasonable to investigate patients with reversible ischaemic cerebral symptoms in order to identify those with a 70% or greater stenosis who will benefit from endarterectomy. Those with lesser degrees of stenosis can be treated medically and followed up; those who progress to more than 70% diameter stenosis can then be considered for surgery.

The situation regarding the examination of patients with asymptomatic carotid bruits is also complex. The authors, along with many people, would wish to know the status of their arteries if they were found to have an asymptomatic carotid bruit. However, a Cochrane Review of surgery for asymptomatic stenosis concluded that ‘for most people with a narrowing of the carotid artery which is not causing any symptoms a surgical operation carries a risk and has little benefit’. The review found that the absolute risk reduction from surgery on patients with > 60% stenosis (NASCET) was only 1% a year, for centres with a surgical complication rate of < 3%. More recent studies have concluded that as ‘best medical therapy’ continues to improve, surgery for asymptomatic carotid stenosis is no longer indicated. ^, Ultrasound will therefore have a role in the identification of those patients who might be considered for endarterectomy, in those centres which offer surgery. However, if there is a policy not to offer surgery to asymptomatic patients, then it might be argued that an ultrasound examination is unnecessary.

Atypical Symptoms

Some patients have unusual symptoms which may or may not be related to carotid disease. Atypical migraine, hyperventilation attacks and temporal lobe epilepsy may sometimes be difficult to diagnose and, in some patients, the possibility of carotid disease might be considered. Ultrasound is of value in excluding carotid disease as a cause of the symptoms in this group of patients, although some care must be given to patient selection to prevent large numbers of unnecessary examinations.

Patients at Risk of Perioperative Stroke

Arterial disease is usually a generalised process, although it affects different arterial territories to varying degrees. Therefore, patients undergoing surgery for conditions such as coronary artery disease, peripheral arterial disease and aortic aneurysms may also have significant carotid disease; there is concern that perioperative morbidity from strokes can be increased in these patients as a result of emboli or inadequate perfusion. Diabetics can also have severe arterial disease and are at risk from perioperative strokes when undergoing major surgery. A review of carotid artery disease and stroke during coronary artery bypass surgery showed that patients without carotid disease had a < 2% stroke rate and this only rose to 3% in patients with an asymptomatic stenosis > 50%; it also drew attention to the role of aortic arch disease in the aetiology of strokes in coronary artery bypass graft patients. For patients with symptoms, ultrasound assessment of the carotids is valuable to allow decisions on modification to surgical bypass technique, or whether carotid endarterectomy should also be considered in addition to the surgery for the primary condition. However, this decision would depend on the relative urgency of the primary condition and many centres, whilst taking note of the carotid disease, will proceed with the main operation and consider subsequent endarterectomy in symptomatic patients.

Postendarterectomy Patients

Complications following endarterectomy can be divided into three groups based on the timing of the events.

• 1.

  Early occlusion due to thrombosis, occurring within the first 24–48 hours after the operation.

• 2.

  Stenosis developing over 12–18 months due to neointimal hyperplasia.

• 3.

  Recurrence of atheroma over a period of several years, resulting in restenosis.

Colour Doppler ultrasound provides a rapid and straightforward method for diagnosis of these complications.

Routine follow-up of asymptomatic patients is not justified by the pick-up rate for developing significant recurrent stenoses, but any patient suffering symptoms related to the operated side should be examined by colour Doppler in the first instance.

Follow-Up of Carotid Stents

Carotid artery stenting is seen as a complementary technique to carotid endarterectomy and can be useful if endarterectomy is problematic or not feasible. Follow-up of stent patients with ultrasound allows early assessment of post-operative in stent restenosis and other complications.

Pulsatile Masses

Colour Doppler ultrasound provides a rapid technique for the assessment of pulsatile neck lumps. There is a variety of causes for these; the main ones are listed in Box 3-3 .

Carotid Dissection

Dissection of the carotid artery may develop from a variety of causes.

• 1.

  It may occur spontaneously, usually consequent upon atheromatous change.

• 2.

  It may result from the extension of an aortic arch dissection.

• 3.

  It may develop following trauma to the neck, such as occurs in whiplash injuries.

• 4.

  As a result of iatrogenic causes, such as carotid catheterisation.

Colour Doppler can be used to identify different flow patterns on either side of the flap, or the presence of a thrombosed channel, and monitor subsequent progress.