Significant progresses have been made in the understanding of the pathological mechanisms of Alzheimer's disease (AD) and in developing tools enabling to detect its stages and its progression in vivo. At present, we know that the changes in AD pathophysiology occur many years before its clinical manifestations. Atrophy of the medial temporal lobe - containing anatomical structures essential for declarative memory, mostly impaired in AD - is one of the biomarkers detectable by magnetic resonance which can help us to predict the progression to dementia in patients with mild cognitive impairment. The atrophy assessment of the posterior cingulate cortex and the precuneus, other key hubs of the declarative memory network, can also be a useful complement.