Abstract
BACKGROUND: Aneurysmal formation after stereotactic radiosurgery (SRS) for vestibular schwannoma (VS) is a rare complication. Its characteristics and the best treatment strategies remain controversial, and the clinical course is especially unknown because reported aneurysms are first incidentally detected, or aneurysmal rupture occurs suddenly, and they are treated immediately. CASE DESCRIPTION: A 68-year-old man who underwent SRS for VS 20 years ago presented with subarachnoid hemorrhage (SAH) due to rupture of a radiation-induced fusiform anterior inferior cerebellar artery aneurysm. He was treated with parent artery occlusion, resulting in a modified Rankin scale grade 2. This report illustrates the first case of detected aneurysm formation before rupture with retrospective magnetic resonance imaging evaluation. CONCLUSION: We describe the possible risk of rapid progression and rupture of aneurysms, focusing on the interval from SRS to aneurysmal formation. The period of formation of SRS-induced aneurysms is suspected to vary from years to decades regardless of radiation doses; however, aneurysms estimated as pseudoaneurysms have an extremely high risk of rupture within a few years, even when small in size. If aneurysms are discovered unruptured, there are some advantages in not only the prevention of poor prognosis due to SAH but also in the availability of optional therapeutic strategies using revascularization. Long-term annual follow-up, including vessel examination, is warranted not only to assess tumor status but also for early detection of any vascular lesions.