Accordion effect and spindle shape deformation can affect high-porosity and flow-diverting stents in the treatment of intracranial aneurysms


A study led by Fabrice Bing, University of Montreal Hospital Research Center, Notre-Dame Hospital, Montreal, Canada, and published ahead of print in Neuroradiology has tested the safety and efficacy of high-porosity and flow-diverting stents to treat intracranial aneurysms when used in vivo.

The authors aimed to find in vivo device deformities in relation to porosity in the part of the device lying over the aneurysm neck. The authors compared in vitro testing with in vivo testing in canines.

The flow diverting stents that were used in the study were Silk 3.5mmx30mm (Balt), Pipeline 4x16mm (ev3/Covidien), which are both commercially available, and a prototype flow-diverting stent—3.75x27mm (Microvention)—the three devices were used for the in vitro experiments. The prototype, according to the authors is a stent-in-stent construction that has an inner flow-diverting mesh attached to an outer high porosity stent.

In the in vitro segment of the study, the authors found that “different flow-diverters had different porosities and pore densities (p=0.001) but the measured porosity and pore density of each flow-diverter did not change significantly when deployed in straight glass tubes within a 1mm range.” Therefore no deformations were observed in in vitro experimentations.

A high porosity stent 4.5x30mm (Microvention) and the flow-diverter prototype stent were used for the in vivo experiments which were conducted in 11 beagles in which aneurysms were created in the right carotid artery. Bing and others predicted that: “The structural uniformity of these self-expanding devices may be altered in vivo due to arterial curves, bifurcations and aneurysm or branch ostia.”

In the study, four weeks post aneurysm creation, high-porosity and flow-diverting stents were implanted to bridge the aneurysm neck and the branch ostium. The authors reported that at two weeks angiography the devices had expanded focally at the level of the aneurysm neck leading to a spindle-shaped deformation. It was found, after the stent constructs were opened longitudinally, that the metallic struts across the aneurysm ostium was not uniform and “followed a reproducible pattern resembling an accordion.”

Bing and colleagues concluded the deformations in vivo did not occur in the in vitro
In the benchtop segment of the study, Bing and colleagues recreated the accordion effect and found that the correlations between the spindle-shaped deformation and the accordion effect was close and significant (0.81; p=0.005).

“The present work shows that substantial alteration in device porosity can occur at the most important portion of the stent, the one which overlies the aneurysm neck or branch origin,” commented Bing and others.

“Virtual and in vitro models do not suffice to understand and predict the in vivo behaviour of flow-diverters and stents in the treatment of aneurysms,” said Bing et al. “In vivo experimentations are needed to measure the true, final porosity of the device and size and number of residual pores in the neointiminal layer covering the aneurysm or branch ostia.”