Song J. Kim, MD

International Stroke Conference 2021
March 17–19, 2021
Session: Advanced Imaging in Intracranial Atherosclerotic Disease: Misnomer or Game-Changer? (24, OnDemand)

A common stroke mechanism accounting for 20-30% of the ischemic strokes worldwide, intracranial atherosclerotic disease (ICAD) is a diagnosis that primarily relies on visualization of luminal narrowing on CTA/MRA. This session expanded upon cutting-edge advances in imaging of ICAD, specifically in revealing plaque morphology, collateral status, and cerebrovascular reserve distal to the stenosis of the culprit lesion.

Before the panel delved into discussion of the advanced imaging, Dr. Achala Vagal provided a comprehensive overview highlighting the limitations of the current conventional lumen-based imaging: failure to detect on-stenosing plaque, compensatory remodeling, and the status of distal flow and collateralization.

Using illustrative real-life examples, Dr. Jeremy Heit underscored the potential utility and gaps in knowledge of perfusion imaging in ICAD; as a widely available imaging modality, it may prove useful in flagging patients presenting with critical, hemodynamically dependent stenosis who can benefit from angioplasty or stent placement. The recently published MyRIAD study did not reveal a significant association between prespecified perfusion threshold of Tmax>4 sec, >10 cc penumbral volume, and recurrent ischemia. We eagerly await a prospective trial identifying an optimal perfusion threshold predictive of recurrent ischemia, which may bring perfusion imaging to the forefront in selecting ICAD patients for advanced treatment.

MR vessel wall imaging, currently limited to use in tertiary academic centers, may characterize unstable plaque morphology at risk of rupture and distal embolism. While there remain challenges including lack of pathological correlation, limited spatial resolution, absent standardization of techniques, there has been a recent accelerated interest among neuro-radiologists and stroke neurologists alike, in examining characteristic ICAD biomarkers on MR vessel wall imaging. Dr. Arindam Chatterjee of Washington University in St. Louis reviewed the 4 hallmark findings identified in a recent meta-analysis published by Song et al. in the January 2021 issue of Stroke: T1 gadolinium enhancement of the plaques, positive remodeling, plaque T1 hyperintensity, and plaque surface irregularity. The study sets the stage for further examining the clinical and prognostic significance of these imaging features.

Finally, Dr. Max Wintermark described the cerebrovascular reserve testing, the principle of which is based on vasodilatory/autoregulatory mechanisms of the intracranial vasculature in response to demand ischemia. Similarly, as in the widely performed cardiac stress tests, the cerebrovascular reserve is “stressed” by administration of carbon dioxide, breath holding, or acetazolamide. He used the examples of patients whose candidacy for EC-IC bypass were determined by demonstration of improved cerebrovascular reserve on perfusion imaging, following acetazolamide challenge. The same testing principle may be applied to ICAD patients in evaluating their candidacy for angioplasty or stenting.