Strokes caused by ICAS are a major global health problem, especially among Asian, Black, and Hispanic populations. Doctors currently focus on the degree that an artery has narrowed to decide on treatment, but this approach isn’t perfect—some people with mild narrowing still have strokes, while others with severe blockages remain fine.

New research suggests that the key to better stroke prevention may lie not just in how narrow the artery is, but in how blood flows through it. This article explores why ICAS is so dangerous, why current treatments fall short, and how studying blood flow patterns could revolutionise stroke care.

Intracranial stenosis: A hidden stroke threat

A global problem with uneven impact

ICAS doesn’t affect everyone equally. While it causes about 10% of strokes in the US, that number jumps to nearly 50% in some Asian countries. This suggests that genetics, diet, or other factors play a big role.

How ICAS causes strokes

There are three main ways a narrowed brain artery can lead to a stroke:

Currently, doctors mostly rely on how much the artery has narrowed to assess risk. But studies show that even a moderate narrowing (50-70%) can be dangerous if blood flow is disrupted—meaning we’re missing something important.

Why current treatments aren’t enough

Similar to cardiology practice, placing a stent (a tiny mesh tube) to prop open the artery might seem like a good solution, but studies have found that stenting actually caused more strokes than medications alone in the short term. There have been three major randomised clinical trials on ICAS treatment where they compared stenting with medical therapy and found that aggressive medical therapy—blood thinners, cholesterol drugs, and blood pressure control—worked better than stenting for preventing strokes. Because of this, stents are now only used in salvage cases where medications fail. Guidelines stipulate that patients need to have had a stroke, been given medication and had another stroke before they can undergo stenting. However, by then, many patients already have permanent disability. Despite this, our treatment solutions are woefully inadequate as even with the best medications, about 8-12% of patients have another stroke within a year.

The big problem: Measuring narrowing of arteries doesn’t tell the whole story

Imagine two people with a 70% blocked artery:

Current imaging (like CT or MRI scans) shows how narrow the artery is, but not how well blood is moving through it. That’s why some people with “mild” blockages have strokes, while others with “severe” narrowing don’t. In cardiology the measurement of blood flow includes the supplementary blood flow and is called the fractional flow reserve (FFR). It is measured by a pressure sensing wire and requires the vessel to be at its maximum dilation to be accurate. In the brain, it is difficult to measure FFR, given the danger of inserting wires into the brain over the narrowing and giving medications to dilate the vessels.

The future: Blood flow as a key to better treatment

What are flow dynamics?

Think of blood flow like water in a river. If the river narrows, the water speeds up, gets turbulent, or even flows backward in some spots. Similarly, when an artery narrows:

New technology lets doctors measure these changes, which could help predict stroke risk better than just looking at narrowing.

New tools to study ICAS

The Vertebrobasilar Flow Evaluation and Risk of Transient Ischemic Attack and Stroke (VERiTAS) study found that measuring blood flow haemodynamics predicted stroke risk better than just looking at how narrow the artery was.¹ Other research shows that abnormal blood flow patterns (like low wall shear stress) are linked to higher stroke risk. Finally, some companies have biomarker blood profiles which can determine if a person is at risk of developing or suffering from atherosclerosis, and if there are unstable plaques in the heart and neck vessels.

What this means for patients

In the future, doctors might:

Conclusion: A smarter way to prevent strokes

Intracranial stenosis is a complex problem, and current treatments don’t work well enough for everyone. The missing pieces are due to a lack of understanding of the mechanisms and fluid dynamics of ICAS, and not just the degree of artery narrowing.

By combining advanced imaging, plaque characteristics and biomarkers with computer modelling, doctors can soon predict strokes more accurately and tailor treatments to each patient’s unique risk. This mindset shift—from asking “How narrow is it?”—could save countless lives by preventing strokes before they strike in this Asian-predominant disease that is widespread in Singapore.