“It’s just a fatty tumor,” owners will often say when I point out a bump under their dog’s skin that rolls under my fingers. “I’m not concerned.” Usually they are right, but I always recommend that owners confirm the diagnosis before going about their day.
Lipomas, benign tumors that consist of fat cells, are one of the most common masses seen in older dogs. Because they are usually benign, it is unlikely for them to spread into adjacent tissue. They tend to appear spontaneously, and they can be monitored the majority of the time.
On occasion, they can be located in an inconvenient location (e.g., under the armpit) or they can grow large enough to be uncomfortable for the dog. In those instances, it’s better to remove them as a matter of comfort.
It’s essential to make sure it really is a lipoma. No vet, no matter how good he or she is, can say with certainty what sort of cells a mass comprises unless he or she takes a look at a sample under a microscope. A fine-needle aspirate is an inexpensive and simple procedure that requires no special equipment and can be performed in the office, without sedation, and gives owners and vets peace of mind when choosing how to manage the mass.
The vast majority of the time, the aspirate confirms the suspicion that the mass is a fatty one. With that diagnosis under their belt, owners can make an informed decision about what to do. But every once in a while, people get a surprise, and are they ever glad they decided to check the mass just to be sure.
Some masses sit under a layer of fat and feel like lipomas but turn out to be something more concerning. Once, I aspirated three suspicious masses on a German shepherd. Two of them were fatty tumors. The third turned out to be a small mast cell tumor, which is an aggressive sort of cancer that has a high probability of metastasizing to internal organs if left alone. The owners were very grateful that they caught this early and were able to have the mass removed before it was a problem for their dog.
Aspirating these masses is a win-win no matter the outcome. If it is a fatty tumor, owners now have peace of mind that they can monitor the dog without rushing into surgery. And in those instances where it does turn out to be something else, owners are always grateful they took the opportunity to catch a problem early before it turned into something much more complicated.