External validation of a grading system predicting ischemia following middle cerebral artery aneurysm clipping

Microsurgical treatment of middle cerebral artery (MCA) aneurysms continues to offer high obliteration rates with acceptable risks, despite an increasing preference for endovascular treatment methods. Yet, the risk of treatment-related ischemia, both symptomatic and radiological, remains a concern. We aimed to externally validate a recently proposed preoperative grading system for predicting risk of ischemic complications after microsurgical treatment of intracranial aneurysms.

We analyzed data from the prospective Helsinki Unruptured Intracranial Aneurysm Quality of Care (HUIQE) study, including 43 consecutive patients who underwent microsurgical clipping for unruptured MCA aneurysms between December 2022 and August 2024. The primary endpoint was the presence of any new diffusion-weighted imaging (DWI) lesions on postoperative MRI within three days after surgery. The preoperative grading system (1 to 6, higher indicating a higher risk for ischemia) was assessed using preoperative imaging data, and its discrimination was evaluated using area under the receiver operating curve (AUROC) analysis.

Postoperative DWI lesions were detected in 67 % of patients. Ischemia was more frequent in older patients (median age 60 vs. 53.5 years, p = 0.0377). New neurological deficits occurred in three patients (7 %); only one (2 %) persisted at 3 months. The observed infarction rates per grade (Grades 1-5: 50 %, 60 %, 83 %, 67 %, and 100 %, respectively) deviated substantially from those reported in the original study (0 %, 3 %, 11 %, 35 %, and 83 %). The AUROC was 0.62, indicating weak discriminative ability.

The grading system displayed poor predictive performance in predicting new postoperative ischemic lesions in our cohort. High radiological infarction rates, even in low-grade cases, challenge the model's clinical utility. These findings highlight the limitations of simplified risk stratification tools in complex microsurgical practice and emphasize the need for critical validation before broad clinical adoption.