title: Influence of thickening of the inner skull table on intracranial volume measurement in older people.
abstract: BACKGROUND
  It is generally assumed that intracranial volume (ICV) remains constant after peaking in early adulthood. Thus ICV is used as a 'proxy' for original brain size when trying to estimate brain atrophy in older people in neuroimaging studies. However, physiological changes in the skull, such as thickening of the frontal inner table, are relatively common in older age and will reduce ICV. The potential influence that inner table skull thickening may have on ICV measurement in old age has yet to be investigated.
  
  
  METHODS
  We selected 60 (31 males, 29 females) representative older adults aged 71.1-74.3years from a community-dwelling ageing cohort, the Lothian Birth Cohort 1936. A semi-automatically derived current ICV measurement obtained from high resolution T1-weighted volume scans was compared to the estimated original ICV by excluding inner skull table thickening using expert manual image processing.
  
  
  RESULTS
  Inner table skull thickening reduced ICV from an estimated original 1480.0ml to a current 1409.1ml, a median decrease of 7.3% (Z=-6.334; p<0.001), and this reduction was more prominent in women than men (median decrease 114.6 vs. 101.9ml respectively). This led to potential significant underestimations of brain atrophy in this sample by 5.3% (p<0.001) and obscured potential gender differences.
  
  
  CONCLUSIONS
  The effects of skull thickening are important to consider when conducting research in ageing, as they can obscure gender differences and result in underestimation of brain atrophy. Research into reliable methods of determining the estimated original ICV is required for research into brain ageing.
authors: Brain Research Imaging Centre, Neuroimaging Sciences, University of Edinburgh, Edinburgh, EH4 2XU, UK.
authors: N A
authors: NA
authors: Royle
authors: M C Valdés
authors: MC
authors: Hernández
authors: S Muñoz
authors: SM
authors: Maniega
authors: B S
authors: BS
authors: Arabisala
authors: M E
authors: ME
authors: Bastin
authors: I J
authors: IJ
authors: Deary
authors: J M
authors: JM
authors: Wardlaw
mesh_terms: D000368:Aged; D000375:Aging / Q000473:pathology*; D001284:Atrophy / Q000473:pathology; D001921:Brain / Q000473:pathology*; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008297:Male; D009929:Organ Size; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012886:Skull / Q000473:pathology*