Diagnosis in life, of Alzheimer’s disease (AD) and Frontotemporal dementia (FTD) is made on clinical grounds, but currently used criteria are burdened with considerable subjective judgments,1,2 and yield an overall accuracy of 81% to 88% in AD cases.3 Given the high prevalence of both diseases and the increasing treatment options,4 simple and sensitive quantitative indicators of both forms of dementia in its early stages would represent valuable clinical tools. Measures of hippocampal atrophy have proven the most sensitive way of differentiating mild to moderate Alzheimer’s disease from non-demented elderly. Of these measures, the width of the temporal horn yields the highest sensitivity, predicting the disease in 73% of cases with 95% specificity.5