Size ratio for clinical assessment of intracranial aneurysm rupture risk.

OBJECTIVES: We previously used three-dimensional (3D) volumetric analysis to identify a novel intracranial aneurysm (IA) morphological metric, aneurysm-to-parent vessel size ratio (SR), which strongly correlated with aneurysm rupture. However, complex 3D analysis is not easily obtained, and ubiquitous IA risk assessment is traditionally performed with two-dimensional (2D) imaging, typically with size being the sole considered morphometric. Because only easily applicable 2D measurements will be of clinical value, we sought to investigate the correlation of SR determined from 2D angiography with IA rupture status. METHODS: SR and traditional aspect ratio (AR) and aneurysm size parameters were measured in a retrospective cohort of 38 IA cases (16 ruptured) with 2D rotational angiographic images. These parameters were analysed for correlation with IA rupture status. Student's t-test or Wilcoxon rank-sum test was used for normally or non-normally distributed data respectively. Logistic regression was performed for independently statistically significant parameters to generate an effect size estimate (odds ratio). Area-under-the-curve (AUC) calculated from the receiver-operating-characteristic curve was additionally obtained for each index to describe differentiating capabilities. RESULTS: Only SR achieved statistical significance (p=0.05) in Wilcoxon rank-sum test. Logistic regression generated an SR odds ratio of 3.52 (p=0.04; 95% confidence interval: 1.035-11.938) for every doubling of SR value. The AUC value of SR (0.688) was higher than that of AR (0.642) and size (0.585). CONCLUSIONS: SR had the strongest correlation with IA rupture and was demonstrated to be a valuable parameter in 2D, where it can be easily obtained from angiographic images. When eventually evaluated in a prospective data set, SR may prove to be an important tool for aneurysm rupture-risk assessment.

In vivo assessment of rapid cerebrovascular morphological adaptation following acute blood flow increase.

OBJECT: Pathological extremes in cerebrovascular remodeling may contribute to basilar artery (BA) dolichoectasia and fusiform aneurysm development. Factors regulating cerebrovascular remodeling are poorly understood. To better understand hemodynamic influences on cerebrovascular remodeling, we examined BA remodeling following common carotid artery (CCA) ligation in an animal model. METHODS: Rabbits were subjected to sham surgery (3 animals), unilateral CCA ligation (3 animals), or bilateral CCA ligation (5 animals). Transcranial Doppler ultrasonography and rotational angiography were used to compute BA flow, diameter, wall shear stress (WSS), and a tortuosity index on Days 0, 1, 4, 7, 14, 28, 56, and 84. Basilar artery tissues were stained and analyzed at Day 84. Statistical analysis was performed using orthogonal contrast analysis, repeated measures analysis of variance, or mixed regression analysis of repeated measures. Statistical significance was defined as a probability value < 0.05. RESULTS: Basilar artery flow and diameter increased significantly after the procedure in both ligation groups, but only the bilateral CCA ligation group demonstrated significant differences between groups. Wall shear stress significantly increased only in animals in the bilateral CCA ligation group and returned to baseline by Day 28, with 52% of WSS correction occurring by Day 7. Only the bilateral CCA ligation group developed significant BA tortuosity, occurring within 7 days postligation. Unlike the animals in the sham and unilateral CCA ligation groups, the animals in the bilateral CCA ligation group had histological staining results showing a substantial internal elastic lamina fragmentation. CONCLUSIONS: Increased BA flow results in adaptive BA remodeling until WSS returns to physiological baseline levels. Morphological changes occur rapidly following flow alteration and do not require chronic insult to affect substantial and significant structural transformation. Additionally, it appears that there exists a flow-increase threshold that, when surpassed, results in significant tortuosity.

Morphology parameters for intracranial aneurysm rupture risk assessment.

OBJECTIVE: The aim of this study is to identify image-based morphological parameters that correlate with human intracranial aneurysm (IA) rupture. METHODS: For 45 patients with terminal or sidewall saccular IAs (25 unruptured, 20 ruptured), three-dimensional geometries were evaluated for a range of morphological parameters. In addition to five previously studied parameters (aspect ratio, aneurysm size, ellipticity index, nonsphericity index, and undulation index), we defined three novel parameters incorporating the parent vessel geometry (vessel angle, aneurysm [inclination] angle, and [aneurysm-to-vessel] size ratio) and explored their correlation with aneurysm rupture. Parameters were analyzed with a two-tailed independent Student's t test for significance; significant parameters (P < 0.05) were further examined by multivariate logistic regression analysis. Additionally, receiver operating characteristic analyses were performed on each parameter. RESULTS: Statistically significant differences were found between mean values in ruptured and unruptured groups for size ratio, undulation index, nonsphericity index, ellipticity index, aneurysm angle, and aspect ratio. Logistic regression analysis further revealed that size ratio (odds ratio, 1.41; 95% confidence interval, 1.03-1.92) and undulation index (odds ratio, 1.51; 95% confidence interval, 1.08-2.11) had the strongest independent correlation with ruptured IA. From the receiver operating characteristic analysis, size ratio and aneurysm angle had the highest area under the curve values of 0.83 and 0.85, respectively. CONCLUSION: Size ratio and aneurysm angle are promising new morphological metrics for IA rupture risk assessment. Because these parameters account for vessel geometry, they may bridge the gap between morphological studies and more qualitative location-based studies.