UCAS (prospective) 

- 2001-2004 in Japan 

- N=5720 patients, 6697 aneurysms (3050 : treatment before rupture @ median of 48 days, 3647: not treated before rupture) 

- Rupture rate of 0.95% per aneurysm-year ; rupture rates associated with 35% mortality, 29% mRS 3-5 

Rupture rates according to location and size:  

Whereas ISUIA found increased rates in all posterior circulation aneurysms, UCAS found higher rupture rates with Acomm and Pcomm (but not more with say, BTAs..... however the total number of VA/BTA aneurysms was small (see below chart)

Graphical representations of rupture rates by location and size: 

Multivariate analyses of predictors of rupture: 

*smoking status (former or current) not associated with rupture rate! 

*previous SAH not predictive of rupture - however only 3% of the cohort had ever had a SAH 

Criticisms: 

- Japanese population: which has the same incidence of aneurysm, but a higher risk of SAH compared to the rest of the world. Unclear if this data can be applied to US or european populations.
- Same selection bias as ISUIA - non-randomized data; the aneurysms believed to be high risk were all treated.