Long-term mortality associated with incidental unruptured intracranial aneurysms in neurologically healthy Japanese adults: the Kashima scan study

BACKGROUND AND PURPOSE: With the widespread use of MRI, there has been an increase in the frequency of incidental detection of unruptured intracranial aneurysms (UIAs); however, the mortality rates and cause of death in adults with incidental UIAs remain unknown. This study aimed to determine whether participants with incidental UIAs have higher mortality rates than those without UIAs among neurologically healthy Japanese adults undergoing self-sponsored brain MRIs. METHODS: This prospective cohort study followed 1670 neurologically healthy Japanese adults (mean age=57.7 years; 47.5% male) who underwent a brain MRI as part of a health check-up (mean follow-up duration=8.7 years). The presence of UIAs was assessed using magnetic resonance angiography. Cox proportional-hazards models were used to evaluate the association between UIAs and mortality after adjusting for age, sex, hypertension, diabetes mellitus and smoking status. RESULTS: UIAs were identified in 90 participants (5.4%). During follow-up, there were 36 fatalities, with malignancy being the leading cause of death (n=15). Mortality rates were significantly higher in participants with UIAs compared with those without UIAs (7.8% vs 1.8%, p=0.002). The presence of UIAs was independently associated with increased mortality risk (adjusted HR=4.95; 95% CIs 2.14 to 11.4). Only one death was attributed to aneurysm rupture in the UIA group. CONCLUSIONS: Neurologically healthy adults with incidental UIAs had significantly higher mortality rates compared with those without UIAs, suggesting that individuals with UIAs should undergo more intensive health monitoring and risk factor management beyond conventional aneurysm surveillance.