Thanks so much for the answers to my questions.
And, no worries about the picture of Sam's lump.
Fortunately, most of the lumps and bumps that dogs develop are benign and are no concern at all. They bother us more than they bother the dogs, in most cases. They rarely cause pain unless they become invasive and affect nerves/muscle.
There are several possible explanations for the lump that you have found, though:
1. Lipomas or fatty tumors can develop anywhere on the body. These are totally benign. They can feel firm if they are underneath muscle. Some of them can become quite large; they tend to be slower growing but in a furry dog, could be easily missed when they are small.
2. Cystic mass....also benign.
3. Small abscess although these are usually a little uncomfortable when felt and often have a small obvious wound or puncture site.
4 Cancer, I am sad to say, can develop in a middle aged dog; it's not only the older ones who might have this problem. It wouldn't be common, but it could happen.
5 Hematoma (blood filled space) or seroma (serum filled space) which could be secondary to trauma of some sort. These wouldn't commonly be found on a leg in my experience, although I include them to be complete.
Unfortunately, it is often not possible to determine what a lump or bump might be based on feel or visualization alone. Usually cells need to be aspirated and examined under a microscope or sent off to a pathologist for review.
And, when it comes to treatment options, we are somewhat limited....we either monitor them, freeze them off if small enough, or surgically remove them.
But, since this lump is not bothering your dog, I wouldn't consider this to be an emergency situation. I might encourage you to have it checked out but you don't have to take him to an emergency hospital.
I hope this helps. Deb