Size Ratio Correlates With Intracranial Aneurysm Rupture Status

Abstract

Background and Purpose-The prediction of intracranial aneurysm (IA) rupture risk has generated significant controversy. The findings of the International Study of Unruptured Intracranial Aneurysms (ISUIA) that small anterior circulation aneurysms (Ͻ7 mm) have a 0% risk of subarachnoid hemorrhage in 5 years is difficult to reconcile with other studies that reported a significant portion of ruptured IAs are small. These discrepancies have led to the search for better aneurysm parameters to predict rupture. We previously reported that size ratio (SR), IA size divided by parent vessel diameter, correlated strongly with IA rupture status (ruptured versus unruptured). These data were all collected retrospectively off 3-dimensional angiographic images. Therefore, we performed a blinded prospective collection and evaluation of SR data from 2-dimensional angiographic images for a consecutive series of patients with ruptured and unruptured IAs. Methods-We prospectively enrolled 40 consecutive patients presenting to a single institution with either ruptured IA or for first-time evaluation of an incidental IA. Blinded technologists acquired all measurements from 2-dimensional angiographic images. Aneurysm rupture status, location, IA maximum size, and parent vessel diameter were documented. The SR was calculated by dividing the aneurysm size (mm) by the average parent vessel size (mm). A 2-tailed Mann-Whitney test was performed to assess statistical significance between ruptured and unruptured groups. Fisher exact test was used to compare medical comorbidities between the ruptured and unruptured groups. Significant differences between the 2 groups were subsequently tested with logistic regression. SE and probability values are reported. Results-Forty consecutive patients with 24 unruptured and 16 ruptured aneurysms met the inclusion criteria. No significant differences were found in age, gender, smoking status, or medical comorbidities between ruptured and unruptured groups. The average maximum size of the unruptured IAs (6.18Ϯ0.60 mm) was significantly smaller compared with the ruptured IAs (7.91Ϯ0.47 mm; Pϭ0.03), and the unruptured group had significantly smaller SRs (2.57Ϯ0.24 mm) compared with the ruptured group (4.08Ϯ0.54 mm; PϽ0.01). Logistic regression was used to evaluate the independent predictive value of those variables that achieved significance in univariate analysis (IA maximum size and SR). Using stepwise selection, only SR remained in the final predictive model (OR, 2.12; 95% CI, 1.09 to 4.13). Conclusion-SR, the ratio between aneurysm size and parent artery diameter, can be easily calculated from 2-dimensional angiograms and correlates with IA rupture status on presentation in a blinded analysis. SR should be further studied in a large prospective observational cohort to predict true IA risk of rupture. (Stroke. 2010;41:916-920.)

Surgical treatment of multiple intracranial aneurysms

“…The size ratio (SR) value of the ruptured aneurysms is significantly larger than unruptured aneurysms. This result is based on the ratio of aneurysms and aneurysmal arteries by Rahman (16). The increased bottleneck factor and the height-width ratio are considered inherent characteristics of the ruptured aneurysms in the control of ruptured and unruptured aneurysms by Hoh (8).…”

Predictible morfometric parameters for ruptrue of intracranial aneurysms – series of 142 operated aneurysms

“…The SR factor is introduced representing the ratio of the caliber of the carrier vessel and the size of the aneurysm as a predisposing factor for aneurysm rupture (8,17,26,31).…”

4 - Intracranial Aneurysms

“…Other researchers such as Weir et al [2] and Nader-Sepahi et al [3] concurred with the correlation between AR and rupture probability. On the other hand, Dhar et al [4], Tremmel et al [5] and Rahman et al [6] reported a high correlation of SR with rupture status. Tremmel et al suggested aneurysms with SRs larger than 2.0 could have a potential risk of rupture.…”

“…Aspect ratio (AR) [1][2][3] and size ratio (SR) [4][5][6] were reported to have significant correlations with probability of aneurysmal rupture, being recognised as promising reference parameters for rupture prediction. AR is a ratio of aneurysmal dome depth to neck width while SR is defined as a ratio of dome length to parent artery diameter.…”