Theoretical model for quantifying the operative benefit of unruptured cerebral aneurysms by location, age and size

Abstract

Aim: The indications for surgery on unruptured asymptomatic cerebral aneurysms are still unclear. Previous mathematical models that have addressed this issue group all aneurysm sizes and locations into one category and report one average rupture and surgical complication rate. In this report the authors used a comprehensive review of the literature and mathematical models to create an online open-access program to quantify the benefit of surgery on unruptured aneurysms according to age, size and location. Materials and methods: Using 5-year prospective International Study of Unruptured Intracranial Aneurysms data and a literature search of 30 additional studies (10,545 patients), we calculated annual rupture rates and operative complication rates for aneurysms by size (5–25 mm), patient age (40–70 years) and 14 common locations. Using this location-, size- and age-specific data, a mathematical model was created by solving differential equations measuring the survival rate of a patient with and without an unruptured aneurysm. Operative benefit was calculated by comparing the quality-adjusted life year outcomes of surgical versus conservative management. Results: We focused on three controversial, high prevalence aneurysm locations (supraclinoid, cavernous and basilar bifurcation). Despite vastly different operative mortality rates and annual rupture rates, 5 mm supraclinoid internal carotid artery aneurysms and basilar bifurcation aneurysms revealed similar operative indications. Small basilar and supraclinoid aneurysms (∼5 mm) only yielded operative benefits in young patients (∼40 years of age). By contrast, larger aneurysms (10 and 15 mm) yielded an operative benefit for a wider range of ages. There was no age and size combination that yielded an operative benefit for cavernous aneurysms. Conclusion: In any mathematical model, some simplifications are inevitable. However, we believe this model is successful in providing helpful estimates and guidelines when delegating patients to surgical or medical management.