Abstract W P82: Natural History Simulation Models: Aneurysms Larger Than 9.5 mm and Aneurysms Growing Faster Than 0.36 mm/year Require Intense Clinical Care

Abstract

Introduction: It is hard to understand aneurysm growth and rupture due to the difficulty of long-term follow-up studies. There are several Markov models which simulate long-term aneurysm growth and rupture, and our study aims to compare two such models and choose the ideal model for our aneurysm database. By understanding the prognosis of the aneurysms, we can identify which aneurysms require invasive treatment. Hypothesis: We hypothesized that there is an ideal model which can accurately simulate the growth and rupture behavior of untreated aneurysms over time. Method: Based on longitudinal data, 290 aneurysms were analyzed in 29 males and 177 females. The mean aneurysm size was 4.5±3.45 mm, and the mean age was 61±13.22 years. We tested Growth Model I and Growth Model II to simulate the growth rate and yearly rupture rate for the next 30 years. For both models, growth and rupture were functions of aneurysm volume. At five-year intervals, we calculated the odds ratio (OR) and used the One-Way ANOVA and Independent T-Test to measure differences in rupture rate for the initial aneurysm diameter and the amount of growth. Results: After 30 years, the mean aneurysm size was 9.18±2.37 mm for Growth Model I and 7.80±6.44 mm for Growth Model II. The mean 30-year rupture rate was 13.93±12.89% for Growth Model I and 14.15±21.96% for Growth Model II. For both models, there was a significantly (p<0.05) higher rupture rate for larger aneurysms and rapidly growing aneurysms at most five-year intervals. Over 30 years, aneurysms larger than 9.5 mm had a 60-80% rupture rate, and aneurysms between 3.5-9.5 mm had a 10-20% rupture rate. Aneurysms growing more than 0.36 mm/year had a 20-35% rupture rate. For aneurysms larger than 9.5 mm, the 30-year OR was 16.04 in Growth Model I and 91.43 in Growth Model II, and for aneurysms growing more than 0.36 mm/year, the 30-year OR was 2.01 in Growth Model I and 7.31 in Growth Model II. Conclusion: In conclusion, any aneurysm larger than 9.5 mm may need immediate surgical treatment. For aneurysms between 3.5-9.5 mm, early surgical intervention is recommended if the growth rate exceeds 0.36 mm/year. Growth Model I is the better model because although both simulations yield similar rupture rates, Growth Model II produces a few unrealistically large aneurysm sizes.