Surveillance Versus Treatment of Unruptured Intracranial Aneurysms of Fortuitous Discovery

The goal of this clinical trial is to determine whether a watchful waiting strategy with imaging surveillance is superior to immediate aneurysm treatment in adults with incidentally discovered unruptured intracranial aneurysms (UIAs). The main questions it aims to answer are: * Does watchful waiting reduce the risk of clinically significant neurological disability compared with immediate treatment? * How do the two strategies compare in terms of aneurysm rupture, treatment-related complications, quality of life, anatomical outcomes, and healthcare costs? Researchers will compare two management strategies: * Immediate selective treatment of the aneurysm (endovascular or neurosurgical treatment according to standard practice). * Watchful waiting with regular clinical and imaging follow-up and no initial aneurysm treatment. Participants will: * Be randomly assigned to either immediate treatment or watchful waiting. * Undergo routine clinical assessments and annual brain imaging for at least 42 months. * Complete quality-of-life questionnaires (EQ-5D-5L) at baseline and annually during follow-up. * Participate in annual telephone follow-up assessments, including evaluation of functional outcome using the modified Rankin Scale (mRS). * Undergo a blood or urine pregnancy test at enrollment if they are women of childbearing potential. The study includes adults aged 35 years or older with incidentally discovered, non-infectious, intradural saccular UIAs measuring between 2.0 mm and 7.9 mm and no history of subarachnoid hemorrhage. The primary objective is to compare the impact of the two management strategies on neurological dependency during follow-up.