Hi Shelagh:
I'm just reading this thread now and wanted to tell you that I also had a boy rat, Tiggies, who had developed something very similar and in the same spot, only on the other side of his face. It came up quickly, like your boy's did, and Tiggie would cry out if I touched the area. I brought him in to the vet, who did a surgery on him to see if it was tumor or abcess; it turned out to be an abcess (like your boys). She told me that these are quite common, especially in male rats and that they can be 'prone to them' and that these abcesses will tend to return. $400 later, but looking good, I brought him home - only to have the abcess flare right back up to its original size the following week!
Well...I decided that I would have to lance it myself, knowing it was full of thick pus, like your boy's looks in the pics; I'd use warm, moist facecloths to soften the skin and just prick and opening into the skin to allow the pus to come out. I kept him on steady antibiotics. It took about 8 months for the abcessing to finally stop and for it to go away.
So, hang in there; as bad as it looks, if you keep the area very clean and keep him medicated, I feel strongly that this will eventually heal.
All best to you.
