[Freesurfer] Corrections in Skull Stripping lead to changes in aseg.stats - underlying reasons

Hello,

After making some corrections to the skull stripping (by hand) and running recon-all I was really puzzled to notice that there had been changes in the aseg.stats.

Here are the statistics:

# Measure lhCortex, lhCortexVol, Left hemisphere cortical gray matter volume, 222913.677586, mm^3 # Measure rhCortex, rhCortexVol, Right hemisphere cortical gray matter volume, 223162.652586, mm^3 # Measure Cortex, CortexVol, Total cortical gray matter volume, 446076.330172, mm^3 # Measure lhCorticalWhiteMatter, lhCorticalWhiteMatterVol, Left hemisphere cortical white matter volume, 197877.640625, mm^3 # Measure rhCorticalWhiteMatter, rhCorticalWhiteMatterVol, Right hemisphere cortical white matter volume, 199335.750000, mm^3 # Measure CorticalWhiteMatter, CorticalWhiteMatterVol, Total cortical white matter volume, 397213.390625, mm^3 # Measure SubCortGray, SubCortGrayVol, Subcortical gray matter volume, 172184.000000, mm^3 # Measure TotalGray, TotalGrayVol, Total gray matter volume, 618260.330172, mm^3 # Measure SupraTentorial, SupraTentorialVol, Supratentorial volume, 976560.279689, mm^3 # Measure IntraCranialVol, ICV, Intracranial Volume, 1340641.214487, mm^3

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# Measure lhCortex, lhCortexVol, Left hemisphere cortical gray matter volume, 221898.779029, mm^3 # Measure rhCortex, rhCortexVol, Right hemisphere cortical gray matter volume, 221558.440924, mm^3 # Measure Cortex, CortexVol, Total cortical gray matter volume, 443457.219953, mm^3 # Measure lhCorticalWhiteMatter, lhCorticalWhiteMatterVol, Left hemisphere cortical white matter volume, 196538.375000, mm^3 # Measure rhCorticalWhiteMatter, rhCorticalWhiteMatterVol, Right hemisphere cortical white matter volume, 199342.906250, mm^3 # Measure CorticalWhiteMatter, CorticalWhiteMatterVol, Total cortical white matter volume, 395881.281250, mm^3 # Measure SubCortGray, SubCortGrayVol, Subcortical gray matter volume, 172740.000000, mm^3 # Measure TotalGray, TotalGrayVol, Total gray matter volume, 616197.219953, mm^3 # Measure SupraTentorial, SupraTentorialVol, Supratentorial volume, 974785.433550, mm^3 # Measure IntraCranialVol, ICV, Intracranial Volume, 1340641.214487, mm^3

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As you can see only the ICV stays the same but everything else changes:

How can this be?

Thank you very much for your answer in advance!

Regards Thomas