It looks a little like the benign histiocytoma's our guys used to get when they were younger. As I recall, the vets told us that with time, they usually resolve. But our furkids were always overactive little guys and kept breaking them open, so we had most of them surgically removed. We always had them checked out by a vet, though, to be sure, so I'm glad you're going in soon and can get a definitive answer!
