An Analysis of the Geometry of Saccular Intracranial Aneurysms
Luciana Parleaa,
Rebecca Fahriga,
David W. Holdsworth,a and
Stephen P. Lowniea
a From the Departments of Medical Biophysics (R.F., D.W.H.), Diagnostic Radiology (D.W.H., S.P.L.), and Clinical Neurological Sciences (S.P.L.), University of Western Ontario, and the J. P. Roberts Research Institute (D.W.H., R.F., L.P.), London, Ontario.
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FIG 1. Schematic diagram of aneurysm measurements.
A, The dimensions measured on the angiographic tracings are the neck width (N), the dome diameter (D), the dome height (H), and the dome semi-axis height (S).
B, For BB aneurysms, the angle, ß, at which the dome tilts with respect to the parent vessel is measured.
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FIG 2. The effect of D/H and H/S ratios on general shape.
A, For a D/H ratio value less than 1, the observed shape is an ellipse, with the major axis in the vertical direction; for a value of 1, a circle; and for values greater than 1, an ellipse, with the major axis in the horizontal direction.
B, For an H/S value less than 2, the aneurysm has a pear shape; for a value of 2, a circle; and for a value greater than 2, a beehive shape.
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FIG 3. Sample angiogram with markers. For estimating true in vivo size, the marker diameters (black arrows) were measured to determine the magnification factor. The diameter of the internal carotid was then measured (white arrow) and divided by the magnification factor in order to obtain the absolute in vivo size
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FIG 4. Distribution of ratios.
A, Distribution of dome diameter/dome height (D/H) for all locations considered.
B, Distribution of dome height/semi-axis height (H/S) for aneurysms located on the BB, MCA, and PcomA.
C, Distribution of dome height/semi-axis height (H/S) for aneurysms located on the AcomA.
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FIG 5. Distribution of the angle at the BB, ß (mean value, 1.6, SD, 23)
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FIG 6. Correlations of absolute in vivo aneurysm dimensions.
A, Dome diameter vs neck width (D vs N); r = .82, D = 1.4 N + 1.7, P < .0001.
B, Dome height vs neck width (H vs N); r = .79, H = 1.3 N + 1.9, P < .0001.
C, Dome height vs dome diameter (H vs D), r = .88, H = 0.8 D + 1.3, P < .0001.
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FIG 7. 3D representations of the typical simple-lobed aneurysm.
A, Two views of the aneurysm arising at the BB, MCA, and PcomA.
B, Two views of the aneurysm arising from the AcomA.
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