If he’s anything like my mom, then probably fairly disturbing but also fascinating and a bit relieving. FWIW, my mother found out she had a similar thing going on. Though she has much more brain matter. In her fifties she slipped and fell. Afterwards she began having dizzy spells and dropping things. She ended up seeing a neurologist where it was discovered that she had, since birth, had this condition and her brain had simply grown around it. It solved a lot of childhood questions for her and brought some comfort in that way, not to mention we were all relieved it wasn’t a malignant tumor. But it’s kind of freaky at the same time.
As it turned out with her the dizzy spells and dropping things was due to inner ear injury from the fall. She’d been coping with her “bubble brain” as she calls it all her life. My mother has a degree and works to this day, she was a teacher for 20 years. No one would ever meet her and think “I bet a significant amount of this woman’s brain is missing!”
