I thought the post said they decided it wasn't spinal leakage?

I'm confused how the vet is saying he needs surgery but they also don't know what is wrong with him. Don't you have to know what you are trying to fix to be able to do surgery? Or is what they are suggesting an exploratory surgery to figure out what is wrong?

I really hope you are able to find out what is wrong and fix the poor guy up. I can't imagine he is anything other than totally miserable with all that swelling. And you said he acted as if it was painful when it wasn't nearly so swollen. OUCH!