Local Recurrence after Microsurgical Clipping of Unruptured Intracranial Aneurysms: Incidence, Timing, and Risk...

This retrospective cohort study evaluated long-term local recurrence rates following microsurgical clipping of anterior circulation unruptured intracranial aneurysms. Between April 2003 and August 2025, 657 patients underwent 700 procedures for 786 aneurysms. Local recurrence was assessed by computed tomography angiography at 5-year intervals. During a mean follow-up of 10.5 ± 3.5 years (6,927.8 patient-years), 9 local recurrences were identified, yielding annual recurrence rates of 0.156% per patient-year and 0.111% per aneurysm-year. Cumulative recurrence-free rates were 100% at 5 years, 99.1% at 10 years, and 98.6% at 15 years. Location-specific analysis revealed significantly higher recurrence rates for internal carotid-anterior choroidal artery aneurysms (0.630% annually) and internal carotid-posterior communicating artery aneurysms (0.262% annually) compared with other locations (p = 0.011). Review of recurrent cases identified 3 mechanistic patterns: closure-line regrowth after parallel clipping (Pattern A, n = 2), residual thin-walled basal footprint in broad-based aneurysms (Pattern B, n = 2), and sub-angiographic remnants preserved for perforator safety (Pattern C, n = 5). The predominance of Pattern C at anterior choroidal artery and posterior communicating artery locations explains the location-specific recurrence risk. All recurrences occurred in aneurysms with complete obliteration (Sindou Grade 0) on early postoperative imaging, whereas no recurrences were observed among 26 cases (3.3%) with small neck remnants (Sindou Grades I-II). Microsurgical clipping of unruptured intracranial aneurysms demonstrated excellent long-term durability with very low local recurrence rates, though the gradual increase beyond 10 years highlights the need for continued surveillance, particularly at locations requiring perforator-preserving techniques.