Relationship between 3D Morphologic Change and 2D and 3D Growth of Unruptured Intracranial Aneurysms

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FIG 1.
Shape index and curvedness. Shape index and curvedness values vary in 3D shapes. The shape index is a descriptor of the local shape of the surface of an object and is scale-invariant. Shape index values range from –1 (concave “cup”) through 0 (saddle point) to 1 (convex “dome”). The curvedness is a positive value to the local curvature of the surface, which usually lies between 0 and 1 and is dependent on the local scale of the object. These values are rotation- and translation-invariant.
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FIG 2.
Nongrowing UIA with statistically significant change in morphology. An example of a ROI around a UIA taken from baseline and follow-up TOF-MRAs made on a Philips 1.5T scanner (Intera/Achieva). The measured UIA shows statistically significant changes in morphology but was considered to be nongrowing (<1-mm change in length or width). The bulge (arrow) that becomes visible on follow-up results in more saddle points on the surface of the UIA, whereby the shape index decreases. The bulge also increases the curvature of the surface of the UIA, resulting in a slightly increased curvedness value.

Table 1:

Patient characteristics

Characteristic
No. of patients	113
No. of aneurysms	127 (102 patient with 1 UIA, 8 with 2 and 3 with 3 UIAs)
Sex (% women)	81 women, 32 men (72% women)
Age at baseline (mean) (yr)	55 (range, 27 –77 )
UIA size at baseline (mean) (mm)	3.8 (SD, 1.9)
Time between baseline and follow-up scan (median) (yr)	4.1 (range, 0.9–13.1 )
Location of aneurysm
Anterior cerebral or communicating artery	25 (20%)
ICA or posterior communicating artery	33 (26%)
MCA	53 (42%)
Posterior circulation	16 (13%)

Table 2:

Change in UIA morphology measurements in relation to continuous UIA 2D and 3D growth^{^a}

Change in	Median (IQR)	Correlation Coefficient (P Value)
Change in	Median (IQR)	2D Growth, Length	2D Growth, Width	3D Growth, Volume
Volume (mm³)	1.60 (−3.70−10.80)	0.29 (<.01)^{^b}	0.28 (<.01)^{^b}	−
Area (mm²)	2.30 (−6.10−11.40)	0.25 (<.01)^{^b}	0.34 (<.01)^{^b}	0.90 (<.01)^{^b}
Compactness 1	0.50 (−1.70−2.60)^{^c}	0.10 (.28)	−0.01 (.89)	0.15 (.09)
Compactness 2	0.01 (−0.04−0.07)	0.09 (.30)	−0.02 (.86)	0.15 (.10)
Elongation	0.01 (−0.03−0.04)	0.01 (.89)	0.02 (.79)	0.09 (.33)
Flatness	0.00 (−0.03−0.04)	0.00 (.97)	0.05 (.58)	0.19 (.03)^{^b}
Sphericity	0.01 (−0.02−0.04)	0.10 (.27)	−0.01 (.94)	0.15 (.09)
Shape index	0.00 (−0.03−0.01)	−0.09 (.32)	−0.17 (.06)	−0.33 (<.01)^{^b}
Curvedness	−0.01 (−0.18−.07)	−0.12 (.16)	−0.15 (.09)	−0.33 (<.01)^{^b}

Note:—IQR indicates interquartile range; −, perfect correlation (same input variable).
↵a The correlation coefficient was calculated with the Pearson or Spearman correlation based on normality of morphologic change.
↵b P values are statistically significant.
↵c All values ×10³.

Table 3:

Change in UIA morphology measurements in growing and nongrowing UIAs^{^a}

Change in	Growing	Nongrowing	P Value
Volume (mm³)	21.92 (4.8−33.23)^{^b}	1.42 (−4.26−9.76)^{^b}	.01^{^b}
Area (mm²)	28.09 (−4.23−35.37)^{^b}	2.07 (−6.47−9.89)^{^b}	<.01^{^b}
Compactness 1	0.40 (−1.35−3.85)^{^b}	0.00 (−1.65−2.33)^{^c}	.21
Compactness 2	0.01 (−0.03−0.11)	0.01 (−0.04−0.06)	.22
Elongation	−0.02 (−0.05−0.02)	0.02 (−0.03−0.04)	.42
Flatness	0.01 (−0.04−0.04)	0.00 (−0.03−0.04)	.37
Sphericity	0.01 (−0.02−0.05)	0.01 (−0.02−0.03)	.20
Shape index	0.00 (−0.13−0.00)	0.00 (−0.03−0.01)	.06
Curvedness	−0.14 (−0.37−0.01)^{^b}	−0.01 (−0.16−0.09)^{^b}	.03^{^b}

↵a Comparing change in 3D quantified morphology of stable and growing UIAs. Values are written as median (IQR). Growth was defined as an increase of at least 1 mm in either width or length of the UIA. P values refer to the relation between parameters of the growing and stable UIAs using a t test or Mann-Whitney U test.
↵b P values are statistically significant.
↵c x 10³.