The Source for Neurovascular News and Education

February 28, 2024

Irregular shape emerged as a better predictor of rupture than size in a Finnish study.

Both size and shape help distinguish which intracranial aneurysms are most likely to rupture, but irregular shape is a better predictor, according to a Finnish study recently published online in Stroke.

Commenting on the findings for Neurovascular Exchange, Hormozd Bozorgchami, MD (Oregon Health & Science University, Portland), pointed out that the ability to discern rupture-prone aneurysms is clinically relevant. In a patient with subarachnoid hemorrhage, ruptured aneurysms may require urgent treatment but unruptured ones can be addressed later in a safer, elective manner, he said.

For their study, Antti E. Lindgren, MD, PhD (Kuopio University Hospital, Kuopio, Finland), and colleagues used the Kuopio Intracranial Aneurysm database from 2003 to 2015 to identify 264 patients with subarachnoid hemorrhage who had a ruptured saccular intracranial aneurysm and at least one additional unruptured saccular aneurysm. Combined, these patients had a total of 268 ruptured and 445 unruptured saccular aneurysms.

Angiographic results of the aneurysms were reevaluated for multiple variables describing aneurysm shape. Multivariate analysis revealed that, among several features, only aneurysm size and irregular shape were independently associated with rupture.

Independent Predictors of Saccular Aneurysm Rupture


Odds Ratio

95% CI

Irregular Shape



Aneurysm Size, per 1 mm



Notably, irregular shape was the strongest independent risk factor for rupture. Location, flow angles, bottleneck factor, and aspect ratio did not emerge as significant predictors.

Confirms Anecdotal Experience

“Our results indicate that irregular aneurysm shape may be used as indicator of ruptured aneurysm in subarachnoid hemorrhage patients with multiple saccular intracranial aneurysms,” Lindgren told NVX in an email. In contrast with conventional wisdom, he said, “irregular shape seems to be a better marker in these cases than aneurysm size.”

Irregular shape is a useful marker of rupture risk, Lindgren explained, because it can be “easily visually assessed from CT-angiography image, [which is] readily available in all units treating patients with subarachnoid hemorrhage.”

Bozorgchami said the study confirms in an objective manner what anecdotal evidence has already suggested about the association between aneurysm shape and rupture risk. What remains to be explored, he said, is how the degree and type of irregularities relate to rupture status. “The study defined anything that is slightly off from a complete sphere as irregular, but there is large degree of variability in irregular aneurysms,” he pointed out.

An important message from the study, he added, is that small aneurysms can and do rupture. “People like to quote ISAT and ISUIA and say those should almost never rupture, but we know that they do,” he stressed. In this series, 53.7% of ruptured aneurysms were smaller than 7 mm and 8.2% were smaller than 8 mm.



Björkman J, Frösen J, Tähtinen O, et al. Irregular shape identifies ruptured intracranial aneurysm in subarachnoid hemorrhage patients with multiple aneurysms. Stroke. 2017;Epub ahead of print.



  • Lindgren reports no relevant conflicts of interest.
  • Bozorgchami reports being a paid consultant for Neuravi.


Related Stories: