MUSC study suggests shorter flow diverters may get better results on carotid artery aneurysms

Researchers at the Medical University of South Carolina found that a nuanced approach to treating intracranial internal carotid artery aneurysms can be done safely and may result in better outcomes than a more widely used version. “It’s technically more challenging,” said Alejandro Spiotta, M.D. “Very few people are attempting this.”

But he hopes that will change as other experienced neurosurgeons read about his team’s study in the journal Scientific Reports. It involves using a smaller version of a device called a flow diverter stent that, as the name suggests, diverts the flow of blood, reducing the risk that an intracranial aneurysm will rupture. It can also help the artery heal over time.

The long and (very) short of flow diversion

Flow diversion is considered a minimally invasive procedure. Surgeons place neurovascular stents, mesh metal tubes, in weak areas of arteries in patients’ brains.

“It's called flow remodeling because the flow prefers to go down the barrel of the stent to the brain. It can still go into the aneurysm, but it passes through this mesh, so it goes in more slowly. And the blood percolates, kind of stuck on the outside of the mesh. It essentially is trapping the blood, and it promotes clotting of the blood in the aneurysm.”

 

Spiotta and his team weren’t looking to end flow diversion. They wanted to take a good procedure and see if it could be even better. 

So their study compared using very short flow diverters, 10 to 12 millimeters in length, with traditional flow diverters from 14 to 50 millimeters in length, in people with aneurysms along the curvy carotid siphon.

“This is the novel part that most people just haven't really thought to try to optimize. It’s in the area where the artery's entering the skull. It has a hairpin turn, where it can be hard to deploy the stent,” Spiotta said.

To compensate, he said standard procedure is to use a long flow diverter that covers a lot of territory and makes it easier to ensure the aneurysm is protected from the blood flow that could cause it to burst. And that works well, Spiotta said.

But what if using a shorter flow diverter worked even better? “When we use a shorter one, we don't have to span to where the artery gets bigger upstream,” Spiotta said.

“The maximum optimal flow diversion effect is related to the surface area of metal coverage at the opening of the aneurysm. Where we want the flow diversion to be most optimal is right at that spot and really nowhere else.”

That’s important, because Spiotta said when a longer flow diverter goes into an artery where the blood vessel turns and tapers, it’s not a perfect fit. “So when you put in a four-millimeter [width] device, it wants to open to four millimeters, right. But if it’s in a three- millimeter diameter part of the vessel, it can't fully open. So that device elongates. It's an engineering thing.” 

As a result, he said the mesh may become thinner or thicker than intended. “The ideal diameter provides the ideal surface area. When it's frustrated and constrained, it can't be allowed to open to its full diameter. The stent stretches and elongates. So the surface area of the coverage, which is determined in the aneurysm treatment, goes down. So instead of having 18, 20%, maybe it goes to 12%. It's hard to calculate, but it’s not working optimally.”

Retrospective study

To see if the shorter flow diverter might make a difference, Spiotta and his colleagues studied the records of 263 patients with saccular aneurysms in the intracranial segments of the internal carotid artery who’d been treated with a flow diverter at MUSC Health from 2013 to 2023. Fifty-five of them had been treated with very short flow diverters, which Spiotta and his team have been comfortable using for years. The rest were treated with longer flow diverters.

The primary factor the study focused on was complete aneurysm occlusion at six months and one year. It also analyzed patients’ functional status and whether they needed retreatment.

Spiotta said the occlusion rates among patients with very short flow diverters were comparable to patients with the longer devices. Same with one-year functional outcomes and complication rates.

But what really stood out to his team was the fact that the short flow diverter group had a retreatment rate of 4.3%, compared with 17.4% in the other group. Would that marked difference hold up in a much larger, multi-center study? Spiotta said they’re planning to put that to the test.

Bottom line: Spiotta said the relatively small study at MUSC showed a couple of key things. “Number one, technically speaking, it was doable. So the safety was there with the very short flow diverters. I didn't have missed deployments. I didn't have to drop a second one because I was short or long on one of them.”

Number two: “Having better outcomes would require a much larger study to prove. But at least this initial experience shows that it's not worse. And there's a suggestion that it's actually better” than longer flow diverters, Spiotta said. 

“We’ll see if this hypothesis and the strategy will prove to beneficial to patients. I think it will.”

Other authors of the study published in Scientific Reports include Mohammad-Mahdi Sowlat, M.D.; postdoctoral research fellow Rahim Abo Kasem; Zachary Hubbard, M.D.; medical student and researcher Hallmon Hughes; Conor M. Cunningham, M.D.; Julio Isidor, M.D.; all with MUSC. 

Ahmed Muthana, M.D., at the University of Baghdad in Iraq and Hidetoshi Matsukawa, M.D./Ph.D., of Fukuoka Neurosurgical Hospital in Japan were also part of the research team.

The study was supported by STAR (Stroke Thrombectomy and Aneurysm Registry) funding, and its authors didn’t declare any competing interests relevant to the topic.