Entorhinal verrucae correlate with surface geometry

Entorhinal verrucae are unique, small elevations on the surface of entorhinal cortex, formed due to distinctive clustering of large neurons in entorhinal layer II. In Alzheimer’s disease, the verrucae atrophy as a result of neurofibrillary tangle formation and concomitant neuronal loss. Previously, we found significant decreases in verrucae height, width, surface area, and volume even in the mildest stage of Alzheimer’s disease. In this report, we introduce a new method for analyzing verrucae prominence using measures of their curvature. Smoothed surfaces and curvatures were generated using FreeSurfer ( http://surfer.nmr.mgh.harvard.edu ) from 100 μm 3 ex vivo MRI isosurfaces. We examined the positive and negative components of mean curvature AreaNorm( H+/- ) and Gaussian curvature AreaNorm( K +/− ) in entorhinal cortex. A significant difference was found between entorhinal (n=10) and non-entorhinal cortices (n=9) for both AreaNorm( H+/- ) and AreaNorm( K +/− ). We also validated our curvature analysis through a comparison with previously published verrucae measures derived from manual labels of individual verrucae. A significant positive correlation was found between mean verrucae height and AreaNorm( H+/- ). Both mean verrucae height and volume were significantly positively correlated with AreaNorm( K +/− ). These results demonstrate that K and H are accurate metrics for detecting the presence or absence of entorhinal verrucae. Curvature analysis may be a useful and sensitive technique for detecting local surface changes in entorhinal cortex.