From the Guidelines
Transcranial ultrasound is a useful tool for predicting stroke risk, but its efficacy is limited by technical factors and operator dependence, and it should be used in conjunction with other diagnostic modalities for optimal stroke risk assessment. The technique works by evaluating blood flow through cerebral vessels, detecting stenosis, occlusions, and other abnormalities that may indicate increased stroke risk 1. According to the 2021 guideline for the prevention of stroke, transcranial Doppler (TCD) ultrasound can be used to screen for right-to-left shunt in patients with ischemic stroke or TIA in whom patent foramen ovale (PFO) closure would be contemplated 1.
Key Points
- Transcranial ultrasound can detect microembolic signals, assess collateral circulation, and evaluate cerebrovascular reactivity, all important factors in stroke risk assessment 1.
- The technique is most valuable when assessing the intracranial arteries, especially in patients with carotid stenosis, where it can identify those at higher risk for subsequent stroke 1.
- Technical limitations, including operator dependence and difficulty obtaining adequate acoustic windows, can limit the efficacy of transcranial ultrasound in approximately 10-15% of patients, particularly elderly individuals with thicker temporal bones 1.
- For optimal stroke risk prediction, transcranial ultrasound should be part of a comprehensive evaluation that includes other imaging modalities, clinical risk factors assessment, and laboratory tests 1.
Recommendations
- Transcranial ultrasound should be used in conjunction with other diagnostic modalities, such as CT or MRI of the brain, carotid ultrasonography, and blood tests, to gain insights into the etiology of and planning optimal strategies for preventing recurrent stroke 1.
- The technique should be performed by experienced operators, and results should be interpreted in the context of other diagnostic findings and clinical risk factors 1.
From the Research
Efficacy of Transcranial Ultrasound in Predicting CVA or Stroke Risk
- Transcranial ultrasound is a non-invasive, low-cost, safe, fast, and real-time imaging technology for stroke risk assessment 2.
- The technique can provide useful direct and indirect information about the characteristics of various vessels in both intracranial and extracranial segments 2.
- Measurement of carotid plaque burden is a strong predictor of cardiovascular risk and can be used for the study of genetics and new risk factors such as toxic products of the intestinal microbiome 3.
- Transcranial Doppler (TCD) embolus detection is useful for risk stratification in patients with asymptomatic carotid stenosis (ACS), with patients having two or more microemboli in an hour of monitoring having a higher 1-year risk of stroke 3.
Diagnostic Accuracy of Transcranial Ultrasonography
- Transcranial ultrasonography, including transcranial Doppler (TCD) and transcranial colour-coded duplex/sonography (TCCD/TCCS), demonstrates high diagnostic accuracy in detecting stenosis in patients with acute ischemic stroke 4.
- The pooled sensitivity and specificity of transcranial ultrasonography were 90% and 95%, respectively, with TCCD/TCCS showing higher sensitivity and specificity than TCD 4.
- TCD has been shown to accurately predict complete or any recanalization, with a sensitivity of 92%, a specificity of 88%, and an overall accuracy of 91% 5.
Applications of Transcranial Doppler in Ischemic Stroke
- Transcranial Doppler (TCD) can be used to detect occlusion or stenosis, diagnose increased intracranial pressure, and predict recanalization 5.
- TCD examination can detect microembolic signals (MES) which are associated with an increased risk of stroke, and the number of microemboli can be decreased by antithrombotic therapy 5.
- Contrast-enhanced examination and Valsalva maneuver with continuous TCD monitoring can accurately screen for right-to-left shunt 5.