Growth on my rat

Question

There is a growth on my son's 15mo rat that you can see in the picture. What might it be?

Answer 1

Without physical access to the animal (to feel the growth and do a biopsy) it's impossible to say for sure what it is. However, my dog had a growth that looked almost exactly like that. In his case it was a lipoma - a benign tumor of fat tissue beneath the skin. My dog lived with it for several years and the only problem it ever caused was that we had to widen his harness to accommodate for the added tissue.

A lipoma is a benign tumor made of fat tissue. They are generally soft to the touch, movable, and painless. (Wikipedia)

The "movable" part means that you can easily push the bump around under the skin.

There are also malignant tumors of skin or fat tissue, like liposarcoma:

Together, atypical lipomatous tumors (ALTs) and well-differentiated liposarcomas (WDLs) account for 40–45% of all liposarcomas. They rarely if ever metastasize and therefore are regarded as benign or premalignant tumors. (Wikipedia)

Unless the bump only grew recently and very quickly, I wouldn't worry too much about it. As long as the rat acts normal and doesn't show any signs of pain or stress, I honestly wouldn't treat this. Treatment ultimately means cutting the tumor out, which causes more pain and stress due to wound care. Rats have a typical life span of only 2 - 3 years. At 15 months, this rat is already middle-aged, which also means that their cells - including tumors - grow slower than in a young rat.

However, if this growth appeared only recently and grows rapidly, you should make a vet appointment very quickly. There are several other things that can manifest as a bump, like cysts. These are very painful and cause a chronic inflammation that weakens the body and immune system. It doesn't look like a cyst, but all I have is one photo and I'm not a vet.