Are the Small Intracranial Aneurysms of the Anterior Circulation Score Sensitive Enough to Discriminate Aneurysms at High Risk of Rupture? Retrospective Analysis of 193 Ruptured Aneurysms.
Buhot B, Seznec Y, et al. • AJNR. American journal of neuroradiology • 2026
The SIAAC score demonstrated a sensitivity of only 65.3% for identifying ruptured small anterior circulation aneurysms, meaning it would have failed to accurately stratify rupture risk in a substantial proportion of patients.
Key Findings
Results
The SIAAC score had a sensitivity of 65.3% for discriminating small intracranial aneurysms at high risk of rupture.
Of 193 patients with ruptured aneurysms, 126 were true-positives (65.3%) and 67 were false-negatives (34.7%)
Sensitivity was calculated as True-Positives/(True-Positives + False-Negatives)
A false-negative result meant the SIAAC score would have inappropriately estimated 'low' or 'no' risk of rupture for aneurysms that actually ruptured
The study cohort included consecutive adult patients admitted for SAH caused by rupture of a <7-mm saccular intracranial aneurysm of the anterior circulation between 2012 and 2022
Methods
The study cohort consisted of 193 patients with ruptured small anterior circulation aneurysms included in the final analysis.
63% of patients were women
Mean age was 64 years (SD, 14.3 years)
All patients were admitted with a proven subarachnoid hemorrhage (SAH)
Only saccular intracranial aneurysms smaller than 7 mm of the anterior circulation were included
Data were collected over a 10-year period from 2012 to 2022 at a single institution
Background
The SIAAC score, originally proposed in 2023, lacked external validation prior to this study.
The SIAAC score was designed to stratify rupture risk of small (<7 mm) intracranial aneurysms of the anterior circulation
The score was intended to guide clinical decision-making
External validation was described as 'critical for the responsible clinical application of the predictive model'
This retrospective study represents an external validation attempt using a large cohort of ruptured aneurysms
Discussion
Application of the SIAAC score would not have accurately stratified rupture risk in a substantial proportion of patients had the aneurysm been discovered before rupture.
34.7% of patients (67 of 193) were classified as false-negatives
False-negatives represent patients whose aneurysms ruptured despite the SIAAC score predicting 'low' or 'no' risk
The authors concluded that 'application of the SIAAC score would not have accurately stratified rupture risk (and thereby proposed appropriate management) in a substantial proportion of patients'
This finding raises concerns about the clinical applicability of the SIAAC score for guiding management decisions
What This Means
This research evaluated a scoring system called the SIAAC score, which was designed in 2023 to help doctors decide whether small brain aneurysms (balloon-like bulges in blood vessel walls, less than 7mm in size) in the front part of the brain are likely to rupture and therefore need treatment. The researchers looked back at 193 patients who had already suffered a brain bleed (subarachnoid hemorrhage) caused by one of these small aneurysms, and calculated what the SIAAC score would have predicted for each patient before the rupture occurred.
The study found that the SIAAC score would have correctly identified the rupture risk in only about 65% of cases. This means that for roughly 1 in 3 patients (34.7%), the scoring system would have predicted a 'low' or 'no' risk of rupture — potentially leading doctors to recommend watchful waiting rather than intervention — even though those aneurysms went on to rupture and cause a life-threatening bleed.
This research suggests that the SIAAC score, while potentially useful, may not be sensitive enough to reliably identify all small brain aneurysms at significant risk of rupture. Because this is the first external validation of the score — meaning testing it on patients outside of the original study that created it — these findings highlight the importance of validating medical scoring tools before widespread clinical use. Further refinement of the score or development of additional predictive tools may be needed to better guide treatment decisions for patients with small brain aneurysms.
Buhot B, Seznec Y, Villeneuve L, Sachet M, Vassal F. (2026). Are the Small Intracranial Aneurysms of the Anterior Circulation Score Sensitive Enough to Discriminate Aneurysms at High Risk of Rupture? Retrospective Analysis of 193 Ruptured Aneurysms.. AJNR. American journal of neuroradiology. https://doi.org/10.3174/ajnr.A9161