Object: Despite recent publications of large-scale study data, controversy over the management of unruptured cerebral aneurysms continues. The low rupture rates in the International Study of Unruptured Intracranial Aneurysms (ISUIA) apparently contradicted surgeons' experiences with ruptured aneurysms. In the present study, based on data from the ISUIA, a mathematical model describing the natural history of cerebral aneurysms was developed. With this model, the author aimed to examine the validity of data from the ISUIA and to provide a better treatment guideline for unruptured aneurysms.
Methods: The author made a computer simulation of the natural history of cerebral aneurysms that was used to calculate such figures as the prevalence of unruptured aneurysms, incidence of subarachnoid hemorrhage (SAH), and age and size distribution of both unruptured and ruptured aneurysms. The lifetime lesion rupture probability for individual patients with various ages and aneurysm sizes was also computed, thereby providing a useful index to help patients in the medical decision-making process. The computer model produced a sample of unruptured aneurysms in the general population with a prevalence of 4.2% and a median diameter of 5.8 mm. These unruptured aneurysms--affected by the rupture rate reported in the ISUIA--had a yearly SAH incidence of 19.6 per 100,000 persons. The median diameter of these aneurysms was 9.4 mm.
Conclusions: Findings in the present study validated the results of the ISUIA by showing that the seemingly low rupture rates could explain the statistical data for ruptured aneurysms. With the featured model, the author calculated the lifetime probability of lesion rupture--a useful measure for deciding on the optimal treatment for unruptured aneurysms.