Inflow angle

Inflow angle

The angle separating parent vessel and aneurysm dome main axes.

Maximal intracranial aneurysm size and intracranial aneurysm morphology parameters are used when deciding if an Intracranial aneurysm (IA) should be treated prophylactically. These parameters are derived from postrupture morphology. As time and rupture may alter the aneurysm geometry, possible morphological predictors of a Ruptured intracranial aneurysm should be established in prerupture aneurysms.

Skodvin et al., from University Hospital of Northern NorwayOslo University Hospital Rikshospitalet matched 1:2 with 24 control IAs that remained unruptured during a median follow-up time of 4.5 (interquartile range, 3.7-8.2) yr. Morphological parameters were automatically measured on 3-dimensional models constructed from angiograms obtained at time of diagnosis. Cases and controls were matched by aneurysm location and aneurysm size, patient age and sex, and the PHASES score (population, hypertension, age, size of aneurysm, earlier subarachnoid hemorrhage from another aneurysm, and site of aneurysm) did not differ between the 2 groups.

Only inflow angle was significantly different in cases vs controls in univariate analysis (P = .045), and remained significant in multivariable analysis. Maximal size correlated with size ratio in both cases and controls (P = .015 and <.001, respectively). However, maximal size and inflow angle were correlated in cases but not in controls (P = .004. and .87, respectively).

A straighter inflow angle may predispose an aneurysm to changes that further increase risk of rupture. Traditional parameters of aneurysm morphology may be of limited value in predicting IA rupture 1).

In 2016 Ji et al., concluded that unruptured paraclinoid aneurysms had a high incidence of aneurysm recanalization (AR) after endovascular treatment. An inflow angle of ≥90 degrees and incomplete occlusion were significant predictors of AR 2).

In 2010 the objective of Baharoglu et al., was to evaluate the importance of inflow-angle (IA), the angle separating parent vessel and aneurysm dome main axes.

IA, maximal dimension, height-width ratio, and dome-neck aspect ratio were evaluated in sidewall-type aneurysms with respect to rupture status in a cohort of 116 aneurysms in 102 patients. Computational fluid dynamic analysis was performed in an idealized model with variational analysis of the effect of IA on intra-aneurysmal hemodynamics.

Univariate analysis identified IA as significantly more obtuse in the ruptured subset (124.9 degrees+/-26.5 degrees versus 105.8 degrees+/-18.5 degrees, P=0.0001); similarly, maximal dimension, height-width ratio, and dome-neck aspect ratio were significantly greater in the ruptured subset; multivariate logistic regression identified only IA (P=0.0158) and height-width ratio (P=0.0017), but not maximal dimension or dome-neck aspect ratio, as independent discriminants of rupture status. Computational fluid dynamic analysis showed increasing IA leading to deeper migration of the flow recirculation zone into the aneurysm with higher peak flow velocities and a greater transmission of kinetic energy into the distal portion of the dome. Increasing IA resulted in higher inflow velocity and greater wall shear stress magnitude and spatial gradients in both the inflow zone and dome.

They concluded that Inflow-angle is a significant discriminant of rupture status in sidewall-type aneurysms and is associated with higher energy transmission to the dome. These results support inclusion of IA in future prospective aneurysm rupture risk assessment trials 3).



Skodvin TØ, Evju Ø, Sorteberg A, Isaksen JG. Prerupture Intracranial Aneurysm Morphology in Predicting Risk of Rupture: A Matched Case-Control Study. Neurosurgery. 2019 Jan 1;84(1):132-140. doi: 10.1093/neuros/nyy010. PubMed PMID: 29529238.

Ji W, Liu A, Lv X, Sun L, Liang S, Li Y, Yang X, Jiang C, Wu Z. Larger inflow angle and incomplete occlusion predict recanalization of unruptured paraclinoid aneurysms after endovascular treatment. Interv Neuroradiol. 2016 Aug;22(4):383-8. doi: 10.1177/1591019916641315. Epub 2016 Apr 11. PubMed PMID: 27066815; PubMed Central PMCID: PMC4984388.

Baharoglu MI, Schirmer CM, Hoit DA, Gao BL, Malek AM. Aneurysm inflow-angle as a discriminant for rupture in sidewall cerebral aneurysms: morphometric and computational fluid dynamic analysis. Stroke. 2010 Jul;41(7):1423-30. doi: 10.1161/STROKEAHA.109.570770. Epub 2010 May 27. PubMed PMID: 20508183.

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