Introduction: Predicting outcome after aneurysmal rupture can be challenging. The Southwestern Aneurysm Severity Index (SASI) was developed to aid aneurysm treatment outcome prediction. In this introduction of SASI, we analyzed patients with ruptured aneurysms treated microsurgically. Using this cohort, each SASI element was evaluated to measure its value to the overall index.

Methods: Patients presenting to our institution with ruptured aneurysms from 2000-2014 treated with microsurgery were included. Outcome was defined as GOS at one year (GOS12m) dichotomized to 1-3 vs 4-5. The SASI was composed of multiple prospectively recorded patient demographic, clinical, radiographic and aneurysm specific variables. Univariate and multivariate analyses were used to construct the best predictive models for patient outcome.

Results: We identified 527 eligible patients. The median age was 53 years (IQR: 19) and 72% were female. The GOS12m was 1-3 in 152 patients (28.8%) and 4-5 in 375 patients (71.2%). In the univariate Chi-square analysis, Hunt-Hess (p<.001), Non-neurological ASA (NNASA, p<.001), normal CT (p<.014), SAH (p<.001), ICH (p<.001), IVH (p<.001), hydrocephalus (p<.001), aneurysm location (p=.021), calcification/thrombosis (p=.004), age>64 (p<.001), and size>20mm (p<.001) were significant predictors of GOS12m. In the multivariate stepwise logistic regression, the best predictive model for poor outcome (without Hunt-Hess and/or NNASA) included ICH (OR 2.19, 95%CI 1.54-3.10), IVH (OR 1.99, 95%CI 1.17-3.39), hydrocephalus (OR 1.99, 95%CI 1.17-3.38), location (OR 1.84, 95%CI 1.30-2.60), age>64 (OR 5.09, 95%CI 3.12-8.30), and size>20mm (OR 5.21, 95%CI 2.35-11.57). A scoring system was created utilizing the beta-coefficients from the logistic regression. This scoring system predicts GOS12m with good accuracy (ROC-AUC 0.813, 95%CI 0.773-0.853).

Conclusions: Several elements were identified as being predictive of GOS12m after microsurgery for ruptured aneurysms. SASI was a stronger predictor than each of these individual factors alone and provides an accurate prediction of GOS12m at presentation, thus improving patient or family expectations and possibly guiding therapeutic efforts.

Patient Care: Determining the factors leading to poor outcome after microsurgery for ruptured aneurysms will enable risk stratification to ensure that treatment decisions between patients and physicians can be made with more objectivity.

Learning Objectives: 1. Discuss the major risk factors leading to poor functional outcome at one year after microsurgery for ruptured intracranial aneurysms. 2. Discuss the relative importance of these risk factors in affecting patient outcome and how to utilize these data in treatment decision making.

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