Mass found on husband's brain

My husband who is 42 just underwent 28 days of plasmapheresis and 4 treatments of retuximab for his TTP relapse. With his 6th reaction to the plasma, being the worse, he had neurological problems such as stuttering and unable to speak fluently so the doctors performed an MRI on his brain to see if he had suffered a stroke. What they found is a mass on the back portion of his brain. The stuttering and delayed speech subsided a few hours later. Now, I understand this could be fatty tissue and that would make sense because he has been on prednisone and other steroids for the last month and had fatty tissue develop where the neck meets the shoulder. He was released from the hospital today and we cannot get in to see a neurologist until Dec 1.
Any insight that could help us out.