BACKGROUND: The variable definition of size ratio (SR) for sidewall (SW) vs bifurcation (BIF) aneurysms raises confusion for lesions harboring small branches, such as carotid ophthalmic or posterior communicating locations. These aneurysms are considered SW by many clinicians, but SR methodology classifies them as BIF.
OBJECTIVE: To evaluate the effect of ignoring small vessels and SW vs stringent BIF labeling on SR ruptured aneurysm detection performance in borderline aneurysms with small branches, and to reconcile SR-based labeling with clinical SW/BIF classification.
METHODS: Catheter rotational angiographic datasets of 134 consecutive aneurysms (60 ruptured) were automatically measured in 3-dimensional. Stringent BIF labeling was applied to clinically labeled aneurysms, with 21 aneurysms switching label from SW to BIF. Parent vessel size was evaluated both taking into account, and ignoring, small vessels. SR was defined accordingly as the ratio between aneurysm and parent vessel sizes. Univariate and multivariate statistics identified significant features. The square of the correlation coefficient (R2) was reported for bivariate analysis of alternative SR calculations.
RESULTS: Regardless of SW/BIF labeling method, SR was equally significant in discriminating aneurysm ruptured status (P < .001). Bivariate analysis of alternative SR had a high correlation of R2 = 0.94 on the whole dataset, and R2 = 0.98 on the 21 borderline aneurysms.
CONCLUSION: Ignoring small branches from SR calculation maintains rupture status detection performance, while reducing postprocessing complexity and removing labeling ambiguity. Aneurysms adjacent to these vessels can be considered SW for morphometric analysis. It is reasonable to use the clinical SW/BIF labeling when using SR for rupture risk evaluation.
ABBREVIATIONS: ACHA, anterior choroidal artery
AUC, area under the curve
BIF, bifurcation-type aneurysms
Dmax, largest diameter
H, aneurysm maximal height
OPTHA, ophthalmic artery
PCOM, posterior communicating artery
PV, average parent vessel size
PVsv, average parent vessel size when considering all small vessels
ROC, receiver operating characteristics
SR, size ratio
SR1, size ratio function of H
SR2, size ratio function of Dmax
SR1sv, size ratio function of H when considering all small vessels
SR2sv, size ratio function of Dmax when considering all small vessels
SW, sidewall-type aneurysms