1.1.5 Diagnosis
Carotid stenosis is diagnosed using color duplex ultrasonography, which is widely available and is low-cost. In addition to assessment of the grade of stenosis, the method also makes it possible to identify the plaque morphology (e.g., with an ulcerated surface).
Patients who should undergo duplex evaluation include those who have suffered a focal neurological deficit or amaurosis fugax. Cerebral computed tomography (CT) or magnetic resonance imaging (MRI) can also help exclude other causes of neurological symptoms, such as hemorrhage or tumor. In asymptomatic patients, there are no standard diagnostic recommendations, except when a bypass operation is planned. In this special situation, a duplex ultrasound examination is recommended in patients ≥ 65 years, patients with stenosis of the left main coronary artery, peripheral arterial occlusive disease, nicotine abuse, or a history including cerebral ischemia. Duplex ultrasound screening should also be carried out in asymptomatic patients who have a bruit over the internal carotid artery if the patient’s general condition allows surgical or interventional treatment. When duplex ultrasound results are unclear, the diagnostic accuracy can be increased using supplementary computed-tomographic angiography or magnetic resonance angiography.
In the diagnosis of extracranial vertebral artery stenosis, a noninvasive duplex ultrasound examination is also the procedure of choice. More than 80% of vertebral arteries can be detected using duplex ultrasonography. Digital subtraction angiography is still the “gold standard” for assessing stenosis of the vertebral artery. However, it is associated with a certain rate of morbidity and mortality, albeit low.
1.1.5.1 Doppler/duplex ultrasonography
Examination technique
The examination is best carried out with the examiner positioned behind the patient’s head, as this allows both hands to be used and functional tests can be carried out more easily. The examination is carried out at two levels using a high-frequency (≥ 7.5 MHz) linear probe, including the proximal vascular segments near the aortic arch (to detect any stenoses at the orifices for the common carotid artery, brachiocephalic trunk, subclavian artery, and vertebral artery). Supraclavicular and jugular insonation should be carried out, preferably using a microconvex probe (≥ 7.5 MHz). If this is not available, adapted programming of a low-frequency convex probe can be used, as well as insonation of carotid segments near the base of the skull. Although the bifurcation region is the most frequent site for pathological carotid processes, it is not the only one.
Examination of the carotid system
In addition to demonstration of any extracranial pathology, attention should be given to the Doppler velocities, as an indirect sign of proximal or distal pathologies. Side-to-side Vmean differences in the internal carotid artery showing ≥ 10% pulsatility differences or bilateral pulsatility changes should be assessed as follows:
– Distal circulatory pathway obstruction (stenosis, occlusion)—possibly unilateral in such cases
– Cerebral microangiopathy (Binswanger disease)
– Raised intracranial pressure (edema, bleeding)
– Bradycardia
– Aortic insufficiency
– Proximal circulatory pathway obstruction (prolonged acceleration time)
– Distal arteriovenous malformation or angioma (normal acceleration time)
– Aortic stenosis, reduced ejection fraction
Transcranial Doppler/duplex ultrasonography should be carried out in cases of cerebral pathology with evidence of hemodynamically relevant extracranial processes. If it is not available, insonation of the supratrochlear artery with compression of the facial artery at the mandibular angle and of the superficial temporal artery in front of the tragus should be carried out (preferably at the same time). The findings at the supratrochlear artery reflect the cerebral hemodynamics along with the quality of intracerebral collateralization and can be predictive for watershed infarction.
Flow differences in the supratrochlear artery greater than 1:2 ratio may suggest:
False-negative compression tests may occur due to:
False-positive compression tests may occur due to:
Examination of the subclavian/vertebral artery system
Demonstration of the orifice of the vertebral artery is obligatory, as this is the most frequent site for arteriosclerotic stenoses. Identification of vessels at the orifice using undulation at the mastoid is also necessary. Demonstration of the distal course (V2) allows better visualization of hypoplasia and aplasia, occlusions and dissections. The vertebral arteries are of equal size in only one-quarter of cases; when there are differences in diameter between the two sides, differences in pulsatility and amplitude between the two vertebral arteries are often seen and the Doppler velocities often differ due to an absent or hypoplastic connection between the vertebral and basilar arteries. It is incorrect to conclude from a bilaterally identical Dopplers of the distal vertebral artery that conditions are normal, although this frequently happens.
In cases of proximal occlusion, there is often distal collateral filling in the region of the atlas via occipital branches or other collaterals to the external carotid artery—and insonation should be carried out there as well, at least in these cases.
Differential diagnosis
Arteriosclerosis:
Embolism:
Arterial