Nancy A. Melville

May 16, 2017

LOS ANGELES — An aneurysm severity tool developed to predict outcomes in ruptured intracranial aneurysms may also be useful as a modified prediction tool for outcomes in unruptured aneurysms treated microsurgically, according to new research.

The tool, dubbed the Southwestern Aneurysm Severity Index (SASI), was developed by Vin Shen Ban, MBBChir, and colleagues with the University of Texas (UT) Southwestern Medical Center, in Dallas, Texas.

"With these findings, we propose an up-to-date, clinically applicable scoring system for predicting unruptured aneurysm outcomes," the researchers concluded. "Future work will include the external validation of the scoring system and we invite interested collaborators to get in touch."

"This is a very significant study because it extends on the previous study on ruptured aneurysms and represents the largest single-institutional study collected in such a manner," said Fady T. Charbel, MD, head of the Department of Neurosurgery at the University of Illinois, a discussant for the study at the meeting.

"It eclipses all other [indexes] and provides very valuable information for patient outcomes after surgical clipping."

Their results were presented at the American Association of Neurological Surgeons (AANS) 2007 Annual Meeting.

With prediction of outcomes after intracranial aneurysms — ruptured or unruptured — representing a clinical challenge with important implications, Dr Ban and colleagues developed SASI and have previously reported on its use in predicting outcomes in microsurgically treated ruptured aneurysms.

To develop a modified version of the index to predict unruptured aneurysm outcomes, the authors evaluated 1708 patients presenting at UT Southwestern with unruptured aneurysms between 1996 and 2016 and treated with microsurgery.

The patients, who had a mean age of 54.5 years and were 76.9% female, were categorized according to having had a Glasgow Outcome Scale (GOS) score at discharge of 1 to 3, indicating worse outcomes ranging from death to severe disability (294 [17.2%]) or a GOS score of 4 to 5, indicating moderate disability to good recovery (1414 [82.8%]).

Univariate analysis showed that leading predictors of unfavorable GOS score at discharge were age, sex, non-neurologic American Society of Anesthesiologists (NNASA) scores, aneurysm location, calcification/thrombosis, size greater than 20 mm and intraoperative rupture (all P < .001).

The presence of multiple aneurysms and reoperation on the same aneurysm were not significant in the analysis for unruptured aneurysms.

In further dividing the patients, matched according to patient and clinical characteristics, into a derivation group for the new model and a second validation group (829 patients each), logistic regression analysis further confirmed the strongest risk factors for an unfavorable GOS score at discharge to be large aneurysm (20 mm or greater; odds ratio [OR], 5.293), intraoperative rupture (OR, 2.40), NNASA (OR, 2.23),  age older than 64 years (OR, 2.20), calcification/thrombosis (OR, 1.94), and aneurysm location (OR, 1.8).

A receiver-operating characteristic curve analysis predicted an area under the curve (AUC) of about 80% for the derivation and validation cohorts in predicting GOS score at discharge, with an overall AUC of 0.79 for the two cohorts.

Further calibration of the correlation between the predicted and observed risk of surgery, was considered excellent, with a value of 0.99.

Ban underscored that, despite advancing development in the treatment of aneurysms, the field has been lacking a standard, reliable outcomes index.

"Our understanding of aneurysms is constantly evolving, and up until now, there is no standard prediction tool in use by every neurosurgeon," he told Medscape Medical News.

"Various groups have proposed their versions of a scoring system based on what they thought was important, but ultimately no scoring system is perfect, ours included."

"However, in building the modified SASI for unruptured aneurysms, we included as many pertinent domains as possible — patient demographics, clinical characteristics, and aneurysmal characteristics — to ensure that we end up with a well-rounded model that can closely predict outcomes.

"This is an improvement over previous proposed scales which have opted for simplicity."

Dr Charbel noted that some important limitations of the study include that the GOS score at discharge doesn't reflect improvement of patients over time, and the study was not able to take into account surgeons' experience, which can play a significant role in patient outcome.

"It is nevertheless a very important study, and external validation could help determine if this can be used to help guide us in choosing between surgical and endovascular procedures," he said.

Ban agreed that variables such as surgeon experience and training, as well as other factors, need to be considered.

"Prediction tools are typically helpful as an adjunct in counseling patients and families, and in treatment decision making," he said.

"Ultimately, however, every case is different, and any prediction tool used should be used as a starting point rather than an end point in decision making." ​

The authors have disclosed no relevant financial relationships. Dr Charbel has disclosed relationships with Transonic Inc and Vassol Inc.

American Association of Neurological Surgeons (AANS) 2017 Annual Meeting. Abstract 801. Presented April 24, 2017.

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