Carotid atherosclerosis occurs most frequently in the proximal internal carotid artery (origin) and at the carotid bifurcation. The progression of luminal narrowing and ulceration leads to ischemic stroke or TCI from embolization, thrombosis, or hemodynamic compromise.
This section describes the 4 main diagnostic techniques currently used to identify the degree of carotid stenosis.
Carotid duplex ultrasonography
Carotid duplex ultrasonography is relatively inexpensive, quick, and noninvasive, with high sensitivity and high specificity for diagnosing high-grade carotid stenosis. However, ultrasonography may overestimate the degree of stenosis and is less accurate in individuals with less than 69% stenosis. The accuracy of the results is also very much operator-dependent, resulting in high variability among different ultrasound laboratories. If the ultrasonography findings suggest the need for surgical intervention, it may be prudent to confirm with a second imaging modality.
Magnetic resonance angiography
MRA is more expensive than carotid ultrasonography and cannot be done in patients who are unable to assume a supine position or in those who have ferromagnetic implants and/or pacemakers. However, the 3-dimensional image of the carotid artery produced by MRA is useful in diagnosing high-grade carotid stenosis and provides an anatomic complement to carotid ultrasonography. The use of advanced MRI techniques is being studied to help physicians identify changes in plaque composition that may be useful for prognosticating risk of rupture and stroke.
Computed tomography angiography
Computed tomography angiography (CTA) is superior to carotid ultrasonography for differentiating high-grade carotid stenosis from total occlusion and effectively excludes carotid stenosis that is greater than 70%, making CTA useful as a screening test. If there is disagreement between MRA and carotid ultrasonography results, CTA is useful in adjudicating the findings.
Cerebral angiography remains the gold standard imaging modality for patients with suspected carotid occlusive disease, but its invasive nature and associated morbidity and mortality risk limits its applicability.
Transcranial doppler ultrasonography
Transcranial doppler ultrasonography (TCD) is a useful adjunct to carotid ultrasonography because it gives physicians the ability to evaluate the flow characteristics of intracerebral vessels. This ability enables the identification of high-grade internal carotid stenosis via the examination of the flow patterns of collateral vessels, including the reversal of ophthalmic artery flow.
Excerpted from BCSC 2020-2021 series: Section 1 - Update on General Medicine. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.