You admit that you can't interpret CTs, then you go right ahead and interpret the CT and say that this CT shows atrophy. Is that what you refer to as "reason"?
You got it wrong anyway. The CT does not show atrophy. It cannot possibly show atrophy. Atrophy means deterioration from the prior state. You can't show the condition has worsened without knowing the prior condition.
In everyday words, you must compare a Before and After photo to show the change of condition. All you gave us was "After."
Let's let the docs do the interpreting.
Are you aware of the fact that your post is incorrect?