Patients with pure amnestic MCI (a-MCI) are reported to have cognitively preserved visual processing skills. However, functional and anatomical abnormalities and/or reorganizations might be already detectable in the brain networks that underlie these cognitive functions. To investigate this possibility, we conducted an integrated multi-modal MRI study using task-fMRI, high resolution structural MRI and Diffusion Tensor Imaging (DTI) in 15 a-MCI patients and 15 matched Healthy Elders (HE). Using fMRI data, we identified an Activation Task Related Pattern (ATRP), including areas related to complex visual processing, and a Deactivation Task Related Pattern (DTRP), or default-mode network (DMN). These two networks were further characterized regarding their structural properties (gray matter volumes and white matter pathways). Within the ATRP, we found increased fMRI responses for the a-MCI group in the frontal lobe, and greater involvement of ventral visual areas. However, there were no differences in ATRP-related white matter or gray matter measures. Regarding the DTRP, a-MCI showed spatial functional reorganizations in coincidence with those reported in DMN studies. Moreover, structural abnormalities in a-MCI patients were clearly found in the DTRP (reduced GM volumes and less fiber tract integrity). In summary, the work presented here highlights the importance of conducting integrated multi-modal MRI studies in early stages of dementia based on spared cognitive domains in order to identify incipient functional abnormalities in critical areas of the DMN and their precise anatomical substrates, possibly reflecting early neuroimaging biomarkers in dementia.