This is also of interest for me.
FIP or Lymphoma
My cat has also fluids in the brain.
One vet thinks (thought) it was lymphoma. The second one, a FIP virus.
After taking steroids she has improved greatly, but she has balance problems and a hard time to stand on her legs.
The vet said that the fluids may have cause some damages in her brain and I was thinking of having her checked by a neurologist.
Thank you Meloncoilie for the referral.