From the article:
Former and current smokers had a recurrence rate of 26.3 percent, and accounted for 232 of the 296 aneurysms documented in this study. Never smokers, on the other hand, experienced a recurrence rate of 17.2 percent, accounting for the remaining 64 aneurysms. All subjects had undergone endovascular treatment.
[…]
“We already know that smoking increases the development, growth and risk of rupture of aneurysms,” says Thompson, the John E. McGillicuddy Collegiate Professor of Neurosurgery. “We didn’t know that after endovascular treatment the risk of recurrence of an aneurysm is as clearly related to smoking as we’ve shown in this study.”
Scientists still don’t know exactly why tobacco use leads to an initial aneurysm, but have established some theories. U-M researchers say smoking might affect how well an aneurysm is obliterated in the first place, or may impede the healing process.