A Theoretical Consideration of the Surgical Treatment of Small Unruptured Intracranial Aneurysms

Abstract

Surgical treatment of small, unruptured intracranial aneurysms remains a controversial topic. Recently, some authors have doubted the validity of the low rupture rates of small aneurysms reported in the literature and advocate aggressive surgical treatment of small unruptured aneurysms; however, some theoretical elucidation is necessary to determine whether such aggressive treatment is appropriate. On certain theoretical assumptions, a simulation was performed to examine whether the low rupture rates for small aneurysms could produce a reasonable size distribution of ruptured aneurysms. Second, considering a hypothetical population in which all the unruptured aneurysms over a certain cut-off size are treated, the effect of this policy on reducing the incidence of subarachnoid hemorrhage (SAH) was mathematically analyzed. Then, the contribution of each individual operation to this reduction of SAH incidence was calculated. The low rupture rates reported in the literature produced a reasonable size distribution of ruptured aneurysms (median diameter of 10 mm) in the simulated population. The analysis of the treatment cut-off size showed that, as the cut-off size was progressively lowered to the range of 3-5 mm, further reduction of the incidence of SAH became almost negligible. The contribution of each individual surgery on unruptured aneurysms decreased rapidly as the aneurysm size decreased, and this reduction was proportional to the reduction of the rupture rate of the aneurysm. These results suggest that we should be prudent in providing surgical treatment to small unruptured intracranial aneurysms.