The area is so vascular that swelling isn't an uncommon side-effect. What exactly does the vet want to do in the surgery?
Our Cole had a lot of edema after his neuter--we used cold compresses for a while, then had some of the sera extracted via needle to reduce the swelling. After that, it resolved pretty quickly. I think I'd be leery of more surgery without a very good explanation of what's going on and what the vet intends to do.
Btw, the needle extraction of fluid was done during a regular appointment visit...
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