Strategic bypass for future flow diversion: Converting a terminal-type middle cerebral artery aneurysm to a sidewall configuration.

BACKGROUND: Flow diversion has expanded treatment options for intracranial aneurysms. However, in terminal-type aneurysms incorporating branch origins, complete exclusion remains challenging due to inherent geometric constraints. CASE DESCRIPTION: We present a 34-year-old male with a 17.1 mm terminal-type middle cerebral artery aneurysm involving both M2 branches. Given the patient's young age and long life expectancy, long-term durability and the risk of future recurrence were important considerations. A bypass to the inferior trunk was performed to intentionally exclude the branch from the aneurysm neck, converting the configuration from a terminal-type to a sidewall-type geometry. Complete aneurysm exclusion was achieved with preservation of distal flow, while establishing a future-treatable configuration. This reconstruction was designed not only for immediate cure but also to ensure that future treatment options remain feasible. In the event of recurrence, the modified geometry would allow definitive treatment using flow diversion. CONCLUSION: Strategic bypass represents a strategy-oriented reconstructive concept that overcomes geometric limitations and enables future therapeutic possibilities.