Risk of Aneurysm Residual Regrowth, Recurrence, and De Novo Aneurysm Formation after Microsurgical Clip Occlusion Based on Follow-up with Catheter Angiography.

INTRODUCTION: Established guidelines for radiologic surveillance after microsurgical treatment of intracranial aneurysms are lacking in the literature because of small sample sizes, poor definitions, and heterogeneous use of imaging modalities. We aimed to propose clinically meaningful definitions for postoperative aneurysm residual, recurrence, and de novo aneurysm formation and to analyze our long-term follow-up catheter angiography results in patients with microsurgically treated intracranial aneurysms. METHODS: A retrospective review of all aneurysms treated microsurgically in a consecutive, single-surgeon series from 1997 to present identified patients with long-term follow-up catheter angiography (>1 year after surgery). Clinical and radiologic data were collected for analysis. RESULTS: We identified 240 patients harboring 380 aneurysms (mean follow-up time, 6.0 +/- 3.3 years per patient; range, 1.0-16.8 years). Postoperative residuals were present in 16 out of 346 clipped aneurysms (4.6%), of which only 3 were left unintentionally. Two out of 16 residual aneurysms (12.5%) demonstrated regrowth, with a regrowth risk of 2.1% per year from 93.6 patient-years of angiographic follow-up. Of 326 aneurysms with no postoperative residual, 5 (1.5%) demonstrated aneurysm recurrence, with a recurrence risk of 0.26% per year from 1931.9 patient-years of angiographic follow-up. Eight de novo aneurysms were identified in 240 patients (3.3%), with a risk of 0.6% per year from 1441.9 patient-years of angiographic follow-up. CONCLUSIONS: Microsurgically treated aneurysms have a very low risk of postoperative residuals and aneurysm recurrence. Growth of residuals and de novo aneurysm formation justify following up with catheter angiography 3 to 5 years after microsurgical clipping.