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Abstract
Although dementia has always been somewhat common, it has become even more common among the elderly in recent years. Therefore its early diagnosis is becoming highly important.
In this study, at first the MRI anatomy of the brain in the three different planes was discussed with special focusing on the brain regions mainly affected in dementia such as temporal lobe and hippocampus.
Then the pathological features of the most common causes of dementia were discussed with description of the pathogenesis, the clinical presentation, and the gross & microscopic features of them.
The different MRI techniques are used to diagnose dementia and differentiating its types specially the volumetric MRI, MR spectroscopy, perfusion MRI and fMRI.
AD is characterized by elevated T2 values in the hippocampus, with T2 shortening in the entorhinal cortex and in the globus pallidus, putamen, and caudate nucleus.
The volumetric MRI shows that the atrophy is mainly in medial temporal lobe particularly in entorhinal cortex, hippocampus, and parahippocampal gyrus. In MRS, NAA levels decreased in both temporal and parietal lobes with reduced NAA/Cr and NAA/Cho ratios in the hippocampus, also increased MI, which is a glial marker, in the frontal lobe, parietal lobe, temporal lobe is noted.
In DWI, an increase in ADC and a decrease in fractional anisotropy values have been reported in temporal lobe WM, hippocampus, posterior WM, and corpus callosum. In perfusion MRI, regional hypoperfusion in the parietal association cortices and posterior cingulate gyri is reported in mild AD and frontal hypoperfusion seen with more advanced disease.
In magnetization transfer imaging, there is decreased MTR of the hippocampus. The decrease in MTR is found in the GM of AD and MCI subjects, while the decrease in MTR is found in the WM of only AD subjects. The BOLD-fMRI shows diminished intensity and/or extent of activation in the frontal and temporal regions. Increased activation may be seen in the AD or at-risk groups, and is explained in terms of a compensatory-recruitment hypothesis.