Brain volume, intracranial volume, and dementia

RATIONALE AND OBJECTIVES. Using a large magnetic resonance (MR) imaging dat a set (n = 532), we investigated the utility of total intracranial volume ( TICV) as a correction factor for head size variability when assessing total brain volume (TBV) and the subcortical volumes of the temporal horn of the lateral ventricular system and the hippocampus. METHODS. A uniform tissue segmentation procedure (ANALYZE) was used to calc ulate volumes. Total brain volume was compared with TICV in 357 control sub jects and 175 patients with various dementing and neuropsychiatric disorder s (mixed dementia/neuropsychiatric group). These MR-based TBV/TICV relation ships were compared with actual postmortem (n = 87) values obtained from a study of neurologically healthy subjects at the time of death. Comparisons were also made in which temporal horn and hippocampal volumes were correcte d by TICV and TBV. Lastly, the ability of corrected TBV and temporal horn a nd hippocampal volumes to distinguish subjects in the mixed dementia/neurop sychiatric group from controls was examined by logistic regression. RESULTS. In the control sample, brain volume averaged 9% of TICV, regardles s of age. In contrast, TBV in the mixed dementia/neuropsychiatric subjects showed, on average, a 22% reduction compared with TICV. By plotting TBV/TIC V curves, highly significant but different regression lines emerged, wherei n a reduction in brain volume in conditions of mixed dementia/neuropsychiat ric disorder showed a distinct separation from the norm. The TBV/TICV regre ssion line generated from MR imaging in controls did not differ from the po stmortem TBV/TICV regression line. Logistic regression showed a 96% correct classification of mixed dementia/neuropsychiatric subjects from controls b y using the TBV/TICV ratio. This technique has the advantage that each subj ect serves as his or her own control. CONCLUSIONS. In cases of dementia and neuropsychiatric disorder in persons 65 and older, TBV corrected by TICV readily differentiated this clinical po pulation from controls. This technique is easy and simple to use and has va rious clinical applications. For temporal horn and hippocampal volume, corr ections with TBV rather than TICV may provide more clinically meaningful co rrections.