Update, we spoke to the vet. He said as he didn't know what it was and it definitely wasn't an abscess he would like to do surgery. This is the first time that surgery has been an option with my ratties as the others were too old and there were higher risks. I have always said that I wouldn't put them through surgery. As it stands, the lump isn't causing him any trouble at all, he's eating plenty and is as energetic as ever, I think I might wait and see how he gets on for a little while then see what his options are. Thoughts anyone? I have to add, money isn't the issue, I'd pay almost anything to see my ratties healthy and happy but I don't think surgery is a good choice for him. Please help