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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: In addition, sex-specific subsamples were created to investigate whether differences were an effect of head size or 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.In conclusion, sex plays a minor role for neuroanatomical volume differences; most differences are related to ICV.

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

Coronal view of one participant's brain, with the Freesurfer segmentations superimposed.
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Figure 1: Coronal view of one participant's brain, with the Freesurfer segmentations superimposed.

Mentions: The datasets were analyzed with FreeSurfer 4.50 (http://surfer.nmr.mgh.harvard.edu/) for automatic segmentation and SPM8 (rel. 5236) (www.fil.ion.ucl.ac.uk/spm) for ICV estimation. The volumes of 18 neuroanatomical structures (accumbens, amygdala, brainstem, caudate, cerebellar cortex, cerebellar white matter, cerebral cortex, cerebral white matter, cerebrospinal fluid (CSF), hippocampus, inferior lateral ventricle, lateral ventricle, pallidum, putamen, thalamus, total brain volume, 3rd ventricle, 4th ventricle) were segmented using an automated procedure described previously (Fischl et al., 2002) (Figure 1). In structures that come in pairs, the sum of left and right hemisphere was used. Cortical gray matter was defined as the volume of the cerebral and cerebellar cortex; white matter was defined as the volume of the cerebral and cerebellar white matter; subcortical gray matter was defined as the volume of the accumbens, amygdala, caudate, hippocampus, pallidum, putamen, and thalamus; the ventricles were defined as the volume of the 3rd and 4th ventricle, the inferior lateral and lateral ventricle and the CSF. To avoid bias, all Freesurfer results were visually inspected by a blinded colleague at the Multimodal imaging lab, UCSD, where the data were analyzed, and all subpar datasets removed. ICV was estimated using an automated version of the reverse brain mask method (RBM) (Keihaninejad et al., 2010) called the “automatic reverse brain mask method” by using the “new segment” approach of the SPM8 toolbox, full description in Hansen et al. (2015). This method was recently shown to have improved accuracy compared to the ICV estimate generated by Freesurfer (Hansen et al., 2015) and comparable to the SPM12 results obtained in Malone et al. (2015).


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)

Coronal view of one participant's brain, with the Freesurfer segmentations superimposed.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 1: Coronal view of one participant's brain, with the Freesurfer segmentations superimposed.
Mentions: The datasets were analyzed with FreeSurfer 4.50 (http://surfer.nmr.mgh.harvard.edu/) for automatic segmentation and SPM8 (rel. 5236) (www.fil.ion.ucl.ac.uk/spm) for ICV estimation. The volumes of 18 neuroanatomical structures (accumbens, amygdala, brainstem, caudate, cerebellar cortex, cerebellar white matter, cerebral cortex, cerebral white matter, cerebrospinal fluid (CSF), hippocampus, inferior lateral ventricle, lateral ventricle, pallidum, putamen, thalamus, total brain volume, 3rd ventricle, 4th ventricle) were segmented using an automated procedure described previously (Fischl et al., 2002) (Figure 1). In structures that come in pairs, the sum of left and right hemisphere was used. Cortical gray matter was defined as the volume of the cerebral and cerebellar cortex; white matter was defined as the volume of the cerebral and cerebellar white matter; subcortical gray matter was defined as the volume of the accumbens, amygdala, caudate, hippocampus, pallidum, putamen, and thalamus; the ventricles were defined as the volume of the 3rd and 4th ventricle, the inferior lateral and lateral ventricle and the CSF. To avoid bias, all Freesurfer results were visually inspected by a blinded colleague at the Multimodal imaging lab, UCSD, where the data were analyzed, and all subpar datasets removed. ICV was estimated using an automated version of the reverse brain mask method (RBM) (Keihaninejad et al., 2010) called the “automatic reverse brain mask method” by using the “new segment” approach of the SPM8 toolbox, full description in Hansen et al. (2015). This method was recently shown to have improved accuracy compared to the ICV estimate generated by Freesurfer (Hansen et al., 2015) and comparable to the SPM12 results obtained in Malone et al. (2015).

Bottom Line: In addition, sex-specific subsamples were created to investigate whether differences were an effect of head size or 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.In conclusion, sex plays a minor role for neuroanatomical volume differences; most differences are related to ICV.

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