J Neurosurg. 2026;145(4):890–899
Successful clipping treats a particular aneurysm, not the patient’s lifelong susceptibility to aneurysmal disease. Kawamoto and colleagues document new aneurysms and growth of untreated lesions years after surgery, supporting continued cerebrovascular surveillance. Importantly, the study strengthens the case for long-term follow-up without establishing one optimal imaging interval for every patient.
Study and key findings
This prospective Japanese cohort enrolled 930 patients aged 27–86 years undergoing clipping of asymptomatic anterior-circulation aneurysms between 2003 and 2025. Imaging analysis included 896 patients, with mean follow-up of 8.31 years and 7,117.7 patient-years of observation.
MRA was scheduled annually when no untreated aneurysm remained and every six months when untreated lesions were present. Suspected new lesions or growth were confirmed by CTA and/or catheter angiography.
De novo aneurysms developed in 37 patients, corresponding to 0.52% per year; estimated cumulative incidence reached 8.9% at 15 years. Among 160 untreated aneurysms, 30 grew, an incidence of 2.48% per aneurysm-year and a 15-year cumulative estimate of 35.1%.
Ten patients developed subarachnoid hemorrhage: one from local recurrence, five from untreated aneurysms and four from de novo lesions. No statistically significant clinical predictors of formation or growth were identified.
Interpretation and limitations
The practical decision is whether follow-up can end after satisfactory clipping. These observations argue against assuming that successful local treatment removes risk elsewhere in the cerebral circulation.
Nevertheless, the cohort was highly selected, under a consistent surgical practice, and limited to initially treated asymptomatic anterior-circulation lesions. Few outcome events restricted risk-factor analysis, while relatively few patients remained under observation beyond 15 years.
The authors suggest annual MRA may be reasonable even with untreated lesions, but this was not tested against six-month surveillance in comparable groups. Their suggestion should therefore not be interpreted as demonstrated equivalence. Surveillance of remote vessels also differs from evaluation of the clipping site, where clip artifact may require another imaging modality.
Clinical takeaway
Plan long-term surveillance alongside the initial operation, addressing both untreated lesions and future aneurysm formation. Individualize modality and frequency; these data support continued vigilance, not a universal annual-imaging rule.