Q: My pet rat has a lump on the skin that is the size of a pea. We took it to the veterinarian who pierced it with a needle. It was just full of blood. What should we do? What caused this lump?
A: It is great that you took your pet rat to the veterinarian for the lump you discovered on its skin. And it is also wonderful that you have a veterinarian who treats pet rats. What your veterinarian did is exactly how we try to figure out if “blood-filled” lumps on the skin are benign or are something more menacing. Many times these are harmless cysts that eventually fill up with blood; draining them solves the problem.
Because such cysts can be harmless, we may never know the cause for these cysts. Some cysts are caused by minor trauma to the skin (sometimes due to excessive scratching), an infected hair follicle or even a superficial skin infection. In more serious cases, some forms of cancer can cause blood-filled lumps on the skin.
When the cause is cancer, just draining the blood will not resolve the problem. A bloody cyst can occur as an isolated form of cancer or the cyst could represent a cancer that is spreading. If the lump returns, this does not mean it is cancer, but it is best to return to your veterinarian to have it examined again. At this next visit, rather than just removing the blood, your veterinarian may want to remove the entire lump.