Can intracranial stents help prevent strokes?

Photo of a couple (PantherMedia / Scott Griessel)

Strokes can be caused by narrowed or blocked blood vessels in the brain. The most common way to prevent further strokes in people who have already had this kind of stroke is to use medication. Stents can also be used to keep the blood vessel open. But research shows that they often cause intracranial hemorrhages (bleeding in the brain) when they are put in, which can in turn also cause a stroke.

Strokes occur when part of the brain doesn’t receive any blood, or not enough. This can happen for various reasons. About 10% of all strokes are caused by the narrowing of one of the vessels (stenosis), which is the result of deposits on the walls of the vessel. This may affect vessels inside the brain (intracranial vessels) or outside the brain (extracranial vessels) – such as the carotid arteries in the neck.

If you have already had a stroke, your risk of further strokes is much higher. Antiplatelet drugs can be used to prevent vessels from becoming narrowed or blocked again. These medications stop the platelets in the blood from clumping together and forming deposits on the vessel walls. Acetylsalicylic acid (the drug in medications like Aspirin) and clopidogrel are two antiplatelet drugs that have been approved in Germany and other countries for the prevention of strokes.

Stents are designed to keep vessels permanently open

Antiplatelet drugs may lower the risk of other blockages, but they can’t always prevent them. About 12 to 14% of people who have already had a stroke have another within two years despite taking medication.

Researchers have been looking for ways to keep these vessels open permanently. In recent years, wire mesh stents (vascular supports) have been available for use in preventing intracranial arteries from becoming narrowed or blocked again. A catheter is used to implant these stents. It is first inserted into an artery near the groin and then guided up to the affected section of the blood vessel. A tiny balloon is attached to the tip of the catheter. This balloon is then filled with contrast medium to expand the constricted intracranial artery. Once the vessel has been expanded, the stent, which at this point is also in the catheter, can be placed in the correct position.

Because the implantation of intracranial stents can lead to complications such as cranial bleeding, it is important to carefully consider the pros and cons of this procedure. Researchers from the Institute for Quality and Efficiency in Health Care (IQWiG, Germany) analyzed studies on intracranial stents. The main thing they wanted to know was how safe the implantation of these kinds of stents is, and whether there are any advantages over only using medication to prevent strokes.

The latest research on intracranial stents

The IQWiG researchers found four randomized controlled trials that looked at intracranial stents. The study that produced the most reliable and useful results was the SAMMPRIS Study. It had by far the greatest number of participants and looked into important questions like the effect of these stents on life expectancy and the risk of further strokes. The study also looked into possible side effects of stents.

The SAMMPRIS Study involved a total of 451 participants, each of whom had had a stroke in the previous 30 days. In all cases the affected artery was narrowed by at least 70%. People who had had a stroke within the previous 24 hours were not included in the study.

All participants were randomly allocated to one of two groups. Both groups were given various treatments to minimize stroke risk factors as well as acetylsalicylic acid (the drug in e.g. “Aspirin”) and clopidogrel. Participants in one of the groups also had a stent implanted. The Wingspan stent system was used in this study.

Intracranial stents increased the number of strokes

The results of the SAMMPRIS Study were perhaps surprising: Participants who were also given an intracranial stent were more likely to have a stroke after the procedure than those who did not have a stent implanted. Expressed in numbers, it was found that:

  • Without an intracranial stent, 5 out of 100 people had another stroke within 30 days.
  • With an intracranial stent, 15 out of 100 people had another stroke within 30 days.

In other words, another 10 out of 100 people with an intracranial stent had a stroke.

The cause of the stroke was usually intracranial bleeding related to the implantation procedure. This type of bleeding may occur if the blood vessel is damaged by the catheter while it is being guided towards the restricted or blocked section. The pressure inside the blood vessel also rises during the procedure. If the vessel can’t cope with the pressure, it may also burst and cause bleeding. Deposits may also break away from the vessel wall while it is being expanded, and then be carried away in the bloodstream. If they end up clogging another vessel inside the brain, they may cause a stroke. While the catheter is being guided from the groin to the brain, it can also dislodge deposits in other parts of the body, leading to an embolism.

The research done so far shows that implanting intracranial stents carries considerable risks. Intracranial stents are really only an option if the vessel is dangerously narrow and other treatments haven’t helped. Before having this kind of procedure, the possible risks and benefits need to be weighed very carefully. There isn’t enough good-quality research to know whether intracranial stents can help people who have dangerously narrow blood vessels in their brain.