Prayers from here for Raven. Poor little princess!

I don't know if steroids affect kidneys or not, but they often reduce swelling in a mass like she has. Check with your vet. Could they do a needle biopsy? From what I have read/remember on PT, that is not a painful procedure for cats.

I remember with Lut's Snoopy, she had surgery but was intubated instead of intravenous for anesthetic because of her heart - she had some congenital oddities, and they didn't want to take chances. IF surgery is an option for Raven - maybe after a while on prednisone or the like - the intubation would be safer?

If the surgery stands a good chance of helping her, remember iMom and your friends at PT who can help.

HUGS and more PT Prayers to Raven and her family.