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Marked effects of intracranial volume correction methods on sex differences in neuroanatomical structures: a HUNT MRI study.

Pintzka CW, Hansen TI, Evensmoen HR, Håberg AK - Front Neurosci (2015)

Bottom Line: Sex differences were detected in a few structures; amygdala, cerebellar cortex, and 3rd ventricle were larger in men, but the effect sizes were small.The residuals and ANCOVA methods were most effective at removing the effects of ICV.Adding additional sexual dimorphic covariates to the ANCOVA gave opposite results of those obtained in the ICV-matched subsample or with the residuals method.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroscience, Norwegian University of Science and Technology Trondheim, Norway ; Department of Medical Imaging, St. Olav's University Hospital Trondheim, Norway.

ABSTRACT
To date, there is no consensus whether sexual dimorphism in the size of neuroanatomical structures exists, or if such differences are caused by choice of intracranial volume (ICV) correction method. When investigating volume differences in neuroanatomical structures, corrections for variation in ICV are used. Commonly applied methods are the ICV-proportions, ICV-residuals and ICV as a covariate of no interest, ANCOVA. However, these different methods give contradictory results with regard to presence of sex differences. Our aims were to investigate presence of sexual dimorphism in 18 neuroanatomical volumes unrelated to ICV-differences by using a large ICV-matched subsample of 304 men and women from the HUNT-MRI general population study, and further to demonstrate in the entire sample of 966 healthy subjects, which of the ICV-correction methods gave results similar to the ICV-matched subsample. In addition, sex-specific subsamples were created to investigate whether differences were an effect of head size or sex. Most sex differences were related to volume scaling with ICV, independent of sex. Sex differences were detected in a few structures; amygdala, cerebellar cortex, and 3rd ventricle were larger in men, but the effect sizes were small. The residuals and ANCOVA methods were most effective at removing the effects of ICV. The proportions method suffered from systematic errors due to lack of proportionality between ICV and neuroanatomical volumes, leading to systematic mis-assignment of structures as either larger or smaller than their actual size. Adding additional sexual dimorphic covariates to the ANCOVA gave opposite results of those obtained in the ICV-matched subsample or with the residuals method. The findings in the current study explain some of the considerable variation in the literature on sexual dimorphisms in neuroanatomical volumes. In conclusion, sex plays a minor role for neuroanatomical volume differences; most differences are related to ICV.

No MeSH data available.


Related in: MedlinePlus

Relationship between ICV and brain tissue types. ICV was stratified in groups of 100 ml and groups with less than five participants were excluded. The bars illustrate the relative size (% of ICV) of different brain tissue types with the standard error superimposed. The two top charts are from analysis performed on men and women combined (n = 966). A significant effect of ICV was found for all brain tissue types; the relative size of cortical and subcortical gray matter decreased with increasing ICV, the opposite was found for the relative size of white matter and the ventricles. The lower four charts display the relationship between different brain tissue types and ICV for each sex separately. Women had a significantly larger relative size of gray matter. No effect of sex was found for any of the other investigated brain tissue types. GM, gray matter; WM, white matter; SubcGM, subcortical gray matter.
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Figure 5: Relationship between ICV and brain tissue types. ICV was stratified in groups of 100 ml and groups with less than five participants were excluded. The bars illustrate the relative size (% of ICV) of different brain tissue types with the standard error superimposed. The two top charts are from analysis performed on men and women combined (n = 966). A significant effect of ICV was found for all brain tissue types; the relative size of cortical and subcortical gray matter decreased with increasing ICV, the opposite was found for the relative size of white matter and the ventricles. The lower four charts display the relationship between different brain tissue types and ICV for each sex separately. Women had a significantly larger relative size of gray matter. No effect of sex was found for any of the other investigated brain tissue types. GM, gray matter; WM, white matter; SubcGM, subcortical gray matter.

Mentions: The results from stratifying the ICVs into groups of 100 ml across men and women separately are presented in Table 2 and Figure 5. ICV groups with less than five subjects were excluded. There were no outliers, and there was homogeneity of variances, as assessed by Levene's test. The relative size of cortical [F(7, 952) = 26.86, p < 0.001, partial η2 = 0.165] and subcortical [F(7, 952) = 35.99, p < 0.001, partial η2 = 0.209] gray matter decreased with increasing ICV, the opposite was found for the relative size of white matter [F(7, 952) = 8.46, p < 0.001, partial η2 = 0.059] and the ventricles [F(7, 952) = 7.43, p < 0.001, partial η2 = 0.052].


Marked effects of intracranial volume correction methods on sex differences in neuroanatomical structures: a HUNT MRI study.

Pintzka CW, Hansen TI, Evensmoen HR, Håberg AK - Front Neurosci (2015)

Relationship between ICV and brain tissue types. ICV was stratified in groups of 100 ml and groups with less than five participants were excluded. The bars illustrate the relative size (% of ICV) of different brain tissue types with the standard error superimposed. The two top charts are from analysis performed on men and women combined (n = 966). A significant effect of ICV was found for all brain tissue types; the relative size of cortical and subcortical gray matter decreased with increasing ICV, the opposite was found for the relative size of white matter and the ventricles. The lower four charts display the relationship between different brain tissue types and ICV for each sex separately. Women had a significantly larger relative size of gray matter. No effect of sex was found for any of the other investigated brain tissue types. GM, gray matter; WM, white matter; SubcGM, subcortical gray matter.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4496575&req=5

Figure 5: Relationship between ICV and brain tissue types. ICV was stratified in groups of 100 ml and groups with less than five participants were excluded. The bars illustrate the relative size (% of ICV) of different brain tissue types with the standard error superimposed. The two top charts are from analysis performed on men and women combined (n = 966). A significant effect of ICV was found for all brain tissue types; the relative size of cortical and subcortical gray matter decreased with increasing ICV, the opposite was found for the relative size of white matter and the ventricles. The lower four charts display the relationship between different brain tissue types and ICV for each sex separately. Women had a significantly larger relative size of gray matter. No effect of sex was found for any of the other investigated brain tissue types. GM, gray matter; WM, white matter; SubcGM, subcortical gray matter.
Mentions: The results from stratifying the ICVs into groups of 100 ml across men and women separately are presented in Table 2 and Figure 5. ICV groups with less than five subjects were excluded. There were no outliers, and there was homogeneity of variances, as assessed by Levene's test. The relative size of cortical [F(7, 952) = 26.86, p < 0.001, partial η2 = 0.165] and subcortical [F(7, 952) = 35.99, p < 0.001, partial η2 = 0.209] gray matter decreased with increasing ICV, the opposite was found for the relative size of white matter [F(7, 952) = 8.46, p < 0.001, partial η2 = 0.059] and the ventricles [F(7, 952) = 7.43, p < 0.001, partial η2 = 0.052].

Bottom Line: Sex differences were detected in a few structures; amygdala, cerebellar cortex, and 3rd ventricle were larger in men, but the effect sizes were small.The residuals and ANCOVA methods were most effective at removing the effects of ICV.Adding additional sexual dimorphic covariates to the ANCOVA gave opposite results of those obtained in the ICV-matched subsample or with the residuals method.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroscience, Norwegian University of Science and Technology Trondheim, Norway ; Department of Medical Imaging, St. Olav's University Hospital Trondheim, Norway.

ABSTRACT
To date, there is no consensus whether sexual dimorphism in the size of neuroanatomical structures exists, or if such differences are caused by choice of intracranial volume (ICV) correction method. When investigating volume differences in neuroanatomical structures, corrections for variation in ICV are used. Commonly applied methods are the ICV-proportions, ICV-residuals and ICV as a covariate of no interest, ANCOVA. However, these different methods give contradictory results with regard to presence of sex differences. Our aims were to investigate presence of sexual dimorphism in 18 neuroanatomical volumes unrelated to ICV-differences by using a large ICV-matched subsample of 304 men and women from the HUNT-MRI general population study, and further to demonstrate in the entire sample of 966 healthy subjects, which of the ICV-correction methods gave results similar to the ICV-matched subsample. In addition, sex-specific subsamples were created to investigate whether differences were an effect of head size or sex. Most sex differences were related to volume scaling with ICV, independent of sex. Sex differences were detected in a few structures; amygdala, cerebellar cortex, and 3rd ventricle were larger in men, but the effect sizes were small. The residuals and ANCOVA methods were most effective at removing the effects of ICV. The proportions method suffered from systematic errors due to lack of proportionality between ICV and neuroanatomical volumes, leading to systematic mis-assignment of structures as either larger or smaller than their actual size. Adding additional sexual dimorphic covariates to the ANCOVA gave opposite results of those obtained in the ICV-matched subsample or with the residuals method. The findings in the current study explain some of the considerable variation in the literature on sexual dimorphisms in neuroanatomical volumes. In conclusion, sex plays a minor role for neuroanatomical volume differences; most differences are related to ICV.

No MeSH data available.


Related in: MedlinePlus