Relationship of Growth to Aneurysm Rupture in Asymptomatic Aneurysms ≤ 7 mm: A Systematic Analysis of the Literature

BACKGROUND: The apparent paradox of natural history data suggesting low rupture risk of small asymptomatic aneurysms and the median size of aneurysm rupture remains unexplained. Aneurysm growth rates and their potential relationship with rupture risk have not been well examined in natural history studies. OBJECTIVE: To examine the question of whether small asymptomatic aneurysms <= 7 mm that are followed up over time rupture and to determine the relationship between aneurysm growth and rupture. METHODS: We reviewed all publications on unruptured aneurysms published from 1966 to 2009. We then selected all aneurysms <= 7 mm for which measurements were reported for at least 2 time points and for which initial asymptomatic status and ultimate outcome (rupture vs unruptured) were reported. Using the Mann-Whitney U test, we compared absolute diameter annual growth rate. RESULTS: Our search retrieved 64 aneurysms. Thirty aneurysms ruptured during follow-up, of which 27 were enlarged before rupture (90%). Thirty-four aneurysms did not rupture, of which 24 enlarged during follow-up (71%). There was a statistically significant trend toward larger absolute diameter growth for ruptured aneurysms vs unruptured aneurysms (3.89 +/- 2.34 vs 1.79 +/- 1.02 mm; P < .001), respectively. Annual growth rates for aneurysms for the 2 groups, however, were not statistically different (27.46 +/- 18.76 vs 32.00 +/- 29.30; P = .92). CONCLUSION: Small aneurysms are prone to growth and rupture. Aneurysm rupture is more likely to occur in aneurysms with larger absolute diameter growth, but rupture can also occur in the absence of growth. The annual growth rate in both groups suggests that rate of growth of aneurysms is highly variable and unpredictable, justifying treatment or close diagnostic follow-up.