We present a fully-automated technique for visualizing localized cerebral ventricle shape differences between large clinical subject groups who have received a magnetic resonance (MR) image scan. The technique combines a robust, automated technique for ventricular segmentation with a 3D surface-based radial thickness mapping approach that allows spatially-localized statistical tests of relative shape differences between clinical groups. The technique is used to analyze localized ventricular expansion in Alzheimer's Disease (AD) and mild cognitive impairment (MCI) in a large cohort of community-dwelling elderly individuals (N=339). The resulting maps are the first to chart localized ventricular dilation in a cohort of this size. Besides showing patterns of ventricular expansion that may be consistent with the spatial progression of AD-related pathology, the maps reveal new information about localized ventricular atrophy that may have been overlooked to date. A detailed understanding of spatial atrophy patterns may be useful for early disease detection or for patient monitoring in drug trials.