Quantified aneurysm shape and rupture risk

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Object. The authors investigated whether quantified shape or size indices could better discriminate between ruptured and unruptured aneurysms.

Methods. Several custom algorithms were created to quantifiy the size and shape indices of intracranial aneurysms by using three-dimensional computerized tomography angiography models of the brain vasculature. Data from 27 patients with ruptured or unruptured aneurysms were evaluated in a blinded fashion to determine whether aneurysm size or shape better discriminated between the ruptured and unruptured groups. Five size and eight shape indices were calculated for each aneurysm. Two-tailed independent Student t-tests (significance p < 0.05) were used to determine statistically significant differences between ruptured and unruptured aneurysm groups for all 13 indices. Receiver-operating characteristic—area under curve analyses were performed for all indices to quantify the predictability of each index and to identify optimal threshold values. None of the five size indices were significantly different between the ruptured and unruptured aneurysms. Five of the eight shape indices were significantly different between the two lesion groups, and two other shape indices showed a trend toward discriminating between ruptured and unruptured aneurysms, although these differences did not reach statistical significance.

Conclusions. Quantified shape is more effective than size in discriminating between ruptured and unruptured aneurysms. Further investigation will determine whether quantified aneurysm shape will prove to be a reliable predictor of aneurysm rupture.

Article Information

Address reprint requests to: Robert E. Harbaugh, M.D., Room 3830, Biomedical Research Building, Penn State Hershey Medical Center, 500 University Drive, Hershey, Pennsylvania 17003. email: rharbaugh@psu.edu.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    Illustration of size indices in a representative lesion. Diameter for the noncircular cross-sections are calculated using area and perimeter.

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    Definitions of selected shape indices and accompanying schematic illustrations.

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    Illustrations of the convex hull in a highly undulated aneurysm. Note that the convex hull surface touches the convex regions of the sac wall (C) but not the concave regions similar to a tight elastin membrane wrapped around it.

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    Box plots of the five shape indices that showed statistical significance for comparison between the ruptured and unruptured lesion groups. Size indices are also shown. The aneurysms shown are shaded surface views of the 3D computer models (not to scale).

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    Graph of ROC curves for rupture predictability demonstrating a comparison of the size indices V and Dmax with the three most predictive shape indices. NULL denotes a hypothetical index with zero predictive capability. The farther an index's curve is from the NULL curve, the greater its predictive value. Note that V and Dmax are quite close to NULL, whereas NSI, UI, and EI are much farther away throughout their ranges.

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    Graph demonstrating the correlation between the two indices of lesion ellipticity—AR and EI.

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