A Simple Flow Classification Parameter Can Discriminate Rupture Status in Intracranial Aneurysms

BACKGROUND: A simple dimensionless aneurysm number (An), which depends on geometry and flow pulsatility, was previously shown to distinguish the flow mode in intracranial aneurysms (IA): vortex mode with a dynamic vortex formation/evolution if An > 1, and cavity mode with a steady shear layer if An < 1. OBJECTIVE: To hypothesize that An > 1 can distinguish rupture status because vortex mode is associated with high oscillatory shear index, which, in turn, is statistically associated with rupture. METHODS: The above hypothesis is tested on a retrospective, consecutively collected database of 204 patient-specific IAs. The first 119 cases are assigned to training and the remainder to testing dataset An is calculated based on the pulsatility index (PI) approximated either from the literature or solving an optimization problem (denoted as (P) over capI). Student's t-test and logistic regression (LR) are used for hypothesis testing and data fitting, respectively. RESULTS: An can significantly discriminate ruptured and unruptured status with 95% confidence level (P < .0001). An (using PI) and <(A)over cap>n (using (P) over capI) significantly predict the ruptured IAs (for training dataset An: AUC = 0.85, (A) over capn: AUC = 0.90, and for testing dataset An: sensitivity = 94%, specificity = 33%, (A) over capn: sensitivity = 93.1%, specificity = 52.85%). CONCLUSION: An >1 predicts ruptured status. Unlike traditional hemodynamic parameters such as wall shear stress and oscillatory shear index, An has a physical threshold of one (does not depend on statistical analysis) and does not require time-consuming flow simulations. Therefore, An is a simple, practical discriminator of IA rupture status.