Why would a doctor order a MRI for a patient who might have dementia?

Imagine a patient of mine came over to our clinic, the family was concerned about memory problems, and we do the neuropsychological tests, and we find out that the person has significant problems in memory and maybe another cognitive domain like language or processing speed. Then we notice these cognitive problems are causing that person to have a disability, like being unable to be independent in their day to day activity. So we end up saying this person has dementia. Then we try to figure out why this person has dementia and we have to figure out if this person has Alzheimer’s disease or something else. So we order the MRI for two reasons. Number one is to try to look at the size of the hippocampus, in particular, and if that size is much smaller than age adjusted, then we will feel more confident that it is Alzheimer’s disease. Then we also look at these small vessel diseases, and depending on how many of these small vessel diseases there are, they might actually contribute to the cognitive deficit. They technically slow down the connection, or the highway, in your brain. We call this vascular cognitive impairment or vascular dementia mixed with Alzheimer’s disease.