To conduct a retrospective multicenter cohort study to define benchmark values for best achievable outcomes following microsurgical clipping of unruptured intracranial aneurysms (UIA).

Surgeons strive for the best possible outcome of their surgeries with the greatest possible chance for recovery of the patients. Therefore, monitoring and quality improvement is increasingly important in surgery. For this purpose, different concepts were developed with the aim to assess best achievable results for several surgical procedures and reduce unwarranted variation between different centers. The concept of a benchmark establishes reference values which represents the best possible outcome of high-volume centers and can be used for comparison and improvement. In the past years, the concept of benchmarking attaches greater importance in the field of healthcare, especially in surgery. Benchmark values are established within a patients' cohort for which the best possible outcome can be expected. The aim of our study is the establishment of robust and standardized outcome references after microsurgical clipping of unruptured intracranial aneurysms. After successful implementation of benchmarks from an international cohort of renowned centers, these data serve as reference values for the evaluation of novel surgical techniques and comparisons among centers or future clinical trials.

Inclusion Criteria:

• Patients who went through elective microsurgical clipping of unruptured intracranial aneurysm
• High-volume centers with ≥40 cases per year during the study period

Exclusion Criteria:

• Treatment following subarachnoid haemorrhage
• Clipping following an incomplete occlusion after previous treatment

Patients who went through elective microsurgical clipping of unruptured intracranial aneurysm