Rescue rat with weird lump

Question
Hi, I am semi panicked about a rat I rescued from a local petstore. We never obtain our rats through petstores because of possible health problems, but this one is a hairless that I've been playing with when I go to get my rat food and the store owner said he was going to be put in with the feeder rats because no one wants him due to this large lump on his stomach.

So I brought him home. Yes I'm aware I'm a sucker! The lump is about the size and shape of a gum drop candy and is exactly where you would expect to find a belly button, low on the tummy but on the center line. It is very soft. It is smooth and pink like the rest of him with no obvious scab or head. It moves when you push on it, and you can touch or manipulate it extensively without it appearing to cause him any pain. The store owner was unaware of his exact age but he is young. He was sold to her by the breeder. I would put him at a few months because he is at about 8 inches in length without the tail and he's nicely rounded out.

I can not see any other problems. He has eaten about a dozen lab blocks in the last 24 hours. He urinates and defecates without any apparent difficulty. He's alert and quite playful for a male. He doesn't seem to have any obvious respiratory issues. I'm taking him to the vet day after tomorrow, but I wanted to get your opinion too. The petstore owner said that the breeder told her it was a navel hernia and that it should not require any further treatment or surgery, but I am not necessarily trusting that diagnosis.

Answer
Hi Kara

I am so glad you rescued the little nekkid guy!! How horrible that they would take him and put him with feeders. Well heck, its horrible that rats and mice are even sold as feeders, period!

Its not unheard of to be a mammary tumor even though he is a male, but his age leads me to believe other wise. Usually mammary tumors affect males older than 12 months, usually related to hormone changes alot like it is with females, although females usually don't start developing mammary tumors until closer to menopause age (18 months plus) since mammary tumors are fueled by high estrogen levels associated with cessation of the estrus cycle.

I was going to suggest it being a hernia as well but it is impossible for me to really be certain without seeing him in person and feeling it etc...
However, even if it is a hernia, the breeder is incorrect to assume it can go untreated. Hernias can cause alot of problems internally and I can be doughnuts to dollars the vet will want to operate regardless if is an umbilical hernia or mass of some other origin.

An umbilical hernia means  there is protrusion from part of the intestines through the abdominal wall in the area where the naval is.   If an umbilical hernia becomes large, it can easily cut off the circulation in the intestines and part of the intestines will die from being strangled by the hernia. This is a situation that is dangerous and often fatal. The breeder is wrong to have assumed this is just something to be taken with a grain of salt. There is a slim chance that these correct on their own, but if he has had no changes all this time, there is a chance that there needs to be some medical intervention by a vet that is experienced with rats and a skilled surgeon on small mammals.. Even if the Vet decides to watch it if it is indeed a hernia, at least the little guy is being properly cared for and of course if its a tumor, it will probably need removed as well.

I am hoping it is an abscess....wouldn't that make it  easier for everyone including the little nekkid rat?! But something tells me its not that simple. It probably would have burst by now if it was indeed an abscess.

Hope all goes well...and in fact, I am concerned now as to what is wrong so if you don't mind can you let me know what the vet says?

thanks

Sandy