Is a carotid ultrasound (US) necessary if a computed tomography angiography (CTA) of the head and neck has been performed for stroke workup in an inpatient?

From the Guidelines

In most cases, a carotid ultrasound (US) is not necessary if a CT angiography (CTA) of the head and neck has already been performed as part of an inpatient stroke workup. CTA provides detailed imaging of both the intracranial and extracranial vasculature, including the carotid arteries, with excellent sensitivity and specificity for detecting significant stenosis, dissection, or other vascular abnormalities, as noted in the American College of Radiology guidelines 1. The CTA offers comprehensive evaluation of the arterial system from the aortic arch through the circle of Willis, providing information about plaque morphology, degree of stenosis, and collateral circulation. Carotid ultrasound, while valuable as a screening tool, generally provides less complete information than CTA and would be redundant in this clinical scenario. However, in specific situations—such as when CTA findings are equivocal, when there are contraindications to contrast (though this would have already been considered before the CTA), or when dynamic flow assessment is specifically needed—a supplementary carotid ultrasound might be considered, as suggested by the guidelines for cerebrovascular diseases-stroke and stroke-related conditions 1.

Key Considerations

• CTA of the neck is useful in the initial workup of patients presenting with carotid territory TIA, and current American Heart Association (AHA) guidelines recommend noninvasive imaging of the cervical carotid arteries for patients with TIA or minor stroke who are candidates for CEA or stenting within 48 hours of onset 1.
• Heavy calcifications or calcified plaque on both sides of the lumen can lead to overestimation of the stenosis on CTA, but this does not necessarily warrant a carotid ultrasound in the absence of other indications 1.
• The decision to perform a carotid ultrasound after a CTA should be guided by the specific clinical question that remains unanswered after the CTA and the potential impact on patient management, prioritizing morbidity, mortality, and quality of life outcomes.

Clinical Implications

• Clinicians should weigh the benefits of additional diagnostic testing against the potential risks and costs, considering the comprehensive information already provided by the CTA.
• In the context of inpatient stroke workup, the focus should be on timely and effective management of stroke and its complications, with diagnostic tests tailored to address specific clinical questions and guide treatment decisions.

From the Research

Carotid Ultrasound Necessity After CTA

• The necessity of a carotid ultrasound (US) after a computed tomography angiography (CTA) of the head and neck has been performed for stroke workup in an inpatient can be evaluated based on the diagnostic accuracy and capabilities of CTA.
• Studies have shown that CTA has a high sensitivity and high negative predictive value for carotid disease, making it an excellent screening test for internal carotid artery stenosis 2.
• CTA can quantify stenoses more precisely than ultrasound and detect tandem stenoses, which is important for the workup of acute stroke patients 3.
• However, CTA may not always accurately diagnose carotid occlusions, and pseudo-occlusions can occur, particularly in cases with reduced flow due to carotid T-occlusions or high degree stenosis of the extracranial ICA 4.
• In such cases, additional imaging modalities like digital subtraction angiography (DSA) or carotid US may be necessary to confirm the diagnosis.

Diagnostic Capabilities of CTA

• CTA has been shown to have a pooled sensitivity of 95% and specificity of 98% for the detection of >70% stenoses, even with older single-slice techniques 3.
• Multislice CTA can detect tandem stenoses in the region of the carotid origin from the aorta, the carotid siphon, and the intracranial portion of the carotids 3.
• CTA can provide a comprehensive evaluation of patients with acute stroke by using a combined approach of pre-contrast CT, CT brain perfusion measurements, and CTA to detect the occluded vessel as well as potential concomitant carotid abnormalities 3.

Comparison with Other Imaging Modalities

• Carotid US is a non-invasive imaging modality that can be used to evaluate carotid stenosis, but its accuracy may be limited compared to CTA 2, 3.
• Magnetic resonance angiography (MRA) is another non-invasive imaging modality that can be used to evaluate carotid occlusive disease, but its clinical utility and limitations are still being evaluated 5.
• DSA is considered the gold standard for diagnosing carotid occlusions, but it is an invasive procedure with associated risks 2, 4.