Cat scans: difference between Alzheimer's and stroke?

How do doctors tell the difference between the effects of the disease and damage from a stroke in an Alzheimer's patient? Can the strokes be easily misdiagnosed/ estimated time wrong? How do they know how long ago the strokes were?

It normally takes a few days for a thrombotic stroke to show up on CT as an area of hypodensity. But these are not primarily radiologic diagnoses. When differentiating between dementia of the Alzheimer type and that of the syndrome of multiple small strokes, the diagnosis rests largely on the history of either gradual but rather smooth deterioration or stuttering deterioration in steps. When all else fails, and tests are inconclusive, a basic medical history can still be useful.

Strokes are caused by blockages. The arteries in parts of the body will show blockages from fatty substances or blood clots and they can be anywhere on the body. A stoke leaves you without the function in certain parts of the body like the arms, legs, lungs, heart, or certain areas of the brain.
If he has Alzheimers, then the brain doctors are already assessing him. They are skilled to diagnois his condition.
But if he was not under former care and they do not have a former xray of his brain it will be harder for them to diagnois his condition and exactly what caused it.
Alzheimers patients have a deterioration of brain cells that are generally localized in one part of the brain. This deterioration continues to other parts of the brain. It looks different than a blockage.
Always get several doctors opinions. I never ever get only one. Doctors can make mistakes.

Strokes are usually sudden and Alzheimers is usually more gradual. Google "differential diagnosis and stroke" or "differential diagnosis and Alzheimers" to see what other diseases appear to be Alzheimers or stroke.

Alzheimer's is the most common type of Dementia. Another type is vascular dementia and is associated with problems in the circulation in the brain. The person has lots of mini stroke which damage the brain. The symptoms can be the same as Alzheimer's but the cause is different.
My mother had a minor stroke 4 years a go. She now has Alzheimer's. She had a Cat scan and it was found that the stroke had not damaged the blood vessels of her brain. Where Alzheimer' does through a build up of protein.