Long-term outcomes and lessons learned from treating incidental cerebral aneurysms: a cohort study of 322 patients

OBJECTIVE: To evaluate the long-term outcomes associated with treating incidental unruptured intracranial aneurysms (UIAs). MATERIALS AND METHODS: This retrospective single-center cohort study included 322 patients with 431 UIAs, of which 356 were treated between January 2011 and July 2020. Treatment modalities included coiling, coiling with stenting, clipping, flow diverter stents, and the Woven EndoBridge device. Outcomes were assessed in terms of serious adverse events, recurrence rates, and aneurysm occlusion status based on the modified Raymond-Roy classification (MRRC). RESULTS: The mean patient age was 53.1 years, with a predominance of females (71%). Most aneurysms (95%) were located in the anterior circulation. Clinical and radiological follow-up continued through May 2024 with a mean follow-up of 48.1 months. The perioperative complication rate was 7.0%, with 1.4% of patients experiencing permanent disability at 90 days. Late complications (occurring more than 12 months post-treatment) included one fatal stent thrombosis and one fatal aneurysmal rupture. Additionally, one patient suffered a subarachnoid hemorrhage (SAH) due to a de novo aneurysm, and another bled from a known but untreated aneurysm. The annual non-aneurysmal mortality rate was 0.97%. Recanalization occurred in 20% of aneurysms treated with coils. Seven patients (2.2%) were lost to follow-up. CONCLUSION: Treatment of UIAs may be associated with very late complications, including delayed rupture. Approximately 20% of aneurysms treated with coils recanalized, necessitating long-term imaging surveillance. Non-aneurysmal mortality in this population is also non-negligible. These findings highlight the need for long-term evaluation of UIA treatment outcomes, ideally over a minimum follow-up period of five years.