She sure is precious, I sure do love my Runners. That is def not normal for Runners. If fluid didn’t come out fat may and can be looked like under a microscope. I am not sure if fluid would look like on Xrays. When my dog had what looked like a tumor come up a needle was put into it and fluid was drawn out looked at under a microscope and it was found out to be a fatty tumor.
Yes, my Sheltie's lipomas (fatty tumors) were tested that way too and were subsequently removed. How old is this duck? Can you move this lump from side to side at all under the skin?