Abstract
PurposeIntracranial aneurysms are local dilations of brain vessels. Their rupture, as well as their treatment, is associated with high risk of morbidity and mortality. In this work, we propose shape indices for aneurysm ostia for the rupture risk assessment of intracranial aneurysms.MethodsWe analyzed 84 middle cerebral artery bifurcation aneurysms (27 ruptured and 57 unruptured) and their ostia, with respect to their size and shape. We extracted 3D models of the aneurysms and vascular trees. A semi-automatic approach was used to separate the aneurysm from its parent vessel and to reconstruct the ostium. We used known indices to quantitatively describe the aneurysms. For the ostium, we present new shape indices: the 2D Undulation Index (UI_mathrm{2D}), the 2D Ellipticity Index (EI_mathrm{2D}) and the 2D Noncircularity Index (NCI_mathrm{2D}). Results were analyzed using the Student t test, the Mann–Whitney U test and a correlation analysis between indices of the aneurysms and their ostia.ResultsOf the indices, none was significantly associated with rupture status. Most aneurysms have an NCI_mathrm{2D} below 0.2. Of the aneurysms that have an NCI_mathrm{2D} above 0.5, only one is ruptured, which indicates that ruptured aneurysms often have a circular-shaped ostium. Furthermore, the ostia of ruptured aneurysms tend to have a smaller area, which is also correlated with the aneurysm’s size. While also other variables were significantly correlated, strong linear correlations can only be seen between the area of the ostium with the aneurysm’s volume and surface.ConclusionThe proposed shape indices open up new possibilities to quantitatively describe and compare ostia, which can be beneficial for rupture risk assessment and subsequent treatment decision. Additionally, this work shows that the ostium area and the size of the aneurysm are correlated. Further longitudinal studies are necessary to analyze whether stable and unstable aneurysms can be distinguished by their ostia.
Highlights
Intracranial aneurysms (IAs) are pathological dilations of the cerebral blood vessels
We derived parameters describing the ostia based on commonly used 3D shape parameters: the 2D Undulation Index UI2D, the 2D Ellipticity Index EI2D, and the 2D Noncircularity Index (NCI2D)
For statistical evaluation of ostium shape and rupture risk, we evaluated 84 cerebral aneurysms
Summary
Intracranial aneurysms (IAs) are pathological dilations of the cerebral blood vessels. Such a dilation takes place locally and leads to a bulging of the vessel wall. Aneurysms can rupture, leading to hemorrhage in the brain. Half of the ruptures are fatal, and one-third of surviving patients suffer long-term from neurological or cognitive deficits [27]. 20% of patients carrying IAs have multiple intracranial aneurysms [20]. Localization, internal blood flow and geometry of an aneurysm are important indicators for the risk of rupture [12, 25,28]. Different indices were developed to characterize the shape of the aneurysm sac [30]. Ratios between the aneurysm height or volume and its neck size are cal-
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