There has never been a study done looking at intracranial pressure in autism. My autistic son also has intracranial hypertension with a pressure of 23. This is not a harmless pressure, as any person who actually has IIH will tell you. My son would lose most of his autism symptoms for 2 days after an LP, until after age 6. Then he was simply joyful to feel better, but by then critical periods of neurodevelopment had passed.
I would suspect that any cysts in your brother’s brain were caused by the elevated pressure. Unfortunately most neurologists believe that any pressure under 25 is not significant. but your brother’s is 25. no arguing with that.