A 35-year-old man underwent surgical removal of a compressive pituitary macroadenoma in France four weeks ago and has been receiving pituitary hormone replacement therapy since, including growth hormone. The surgery was uncomplicated, and he initially had a smooth recovery. He has no other medical history. However, he has recently developed poor balance with a broad-based gait and severe forgetfulness over the past one to two weeks. During the examination, you notice an ataxic gain and occasional myoclonic limb movements. His MMSE score is 22/30, and routine blood tests are normal. Based on the probable diagnosis, what abnormalities might you expect to see on his brain MRI?