Good news! Hope he's back to being a terror soon :)
That's good news, and shouldn't cause any trouble. My dog has had a small lipoma (a fatty tumor) outside the muscle on her chest for years. About 1" across. It has never grown bigger, and never causes any discomfort or problems. She also has a smaller one actually within the muscle on her shoulder, and again, that one causes no problems. The vet examined both of them, and said they didn't need to be removed, unless they became much bigger. They never have.
I took him to the vet yesterday, and the vet said that it was just a fatty mass that had grown and had gotten trapped outside of the muscle. My dog had a testicle that never fell, so when he was neutered, they had to make an incision near his belly to remove it. He said that the fat was trapped outside of the muscle when the muscle healed and produced a lump. This was almost a year ago, and this was the first time I had felt this mass, but the vet said there was no need to worry. If it did get much bigger, we could have it removed. I completely trust my vet, so I feel a lot better about this now. THANK YOU all for your help and concern!
Any news from the vet? So far I've had one Scottie and one Airedale with benign growths in their rib cage area. I don't know if it's something all terriers are prone to or not. The Scottie's vet said it was not uncommon in the breed. He was also younger than two when his showed up. He was just fine and had no health problems from it during his life. The Airedale is a rescue and came with the growth, so I don't know what age she got it. I hope that's all that's wrong with your Yorkie!
I wonder if it could be a hernia? But it's impossible for me to tell you exactly what this is. Yes, take him in to see the vet, then he can be properly examined. If it IS a hernia, and it becomes strangulated. it will be extremely painful for him.
If you can, please do update us on what happens.