Tumors are common in rats, but so are abscesses and cysts. If you suspect a lump on your rat’s body is a tumor, it’s worth it to wait 2-4 weeks to see if it is an abscess or cyst instead. Most abscesses are fairly harmless and either clear up on their own or with minor treatment. Generally cysts are also harmless. Abscesses can “pop up” overnight and they tend to grow more quickly than cysts or tumors. With most tumors on the body the skin moves slightly independently of the lump, but abscesses or cysts are usually inside the skin so moving the skin moves the lump.
Abscesses are usually small infections, often caused by bite or scratch wounds, which the skin encapsulates to isolate. The wound usually heals before the abscess appears. However, sterile abscesses can be caused by inflammation due to an injury or a foreign body, such as sutures. After a rat has been neutered, a sterile abscess in the scrotum is common and can be treated as a simple abscess.
It is fairly common for male rats to develop abscesses in the groin area. These often are noticed only after the abscess opens and drains and therefore appear as a hole in the skin. In most cases, groin abscesses heal quickly once they open and drain.
An abscess on the face, in a tooth socket, or near lymph glands, can be more serious, often indicating a cancer. Oral antibiotics should be given for a serious abscess.
An abscess that won’t heal after a week or two of treatment may be a cyst, a sterile abscess caused by a foreign body, or it may indicate a cancer, such as squamous cell carcinoma, especially on the face. You can try to treat a cancer with prednisone at 1 mg/lb twice a day, which in some cases can shrink or slow the growth of a tumor, and try to control the infection with antibiotics, but there is no cure.
A Simple Abscess
In rats, an abscess on the body (including the scrotum) can usually be allowed to progress on its own. The body has a natural healing process to open the abscess so it can drain. This process may take several weeks, but as long as the rat seems well and isn’t bothered by the abscess you don’t have to do anything. Abscesses on the underside of the body generally progress more quickly because gravity helps the opening process. Abscesses on the back can take much longer to open.
The first sign that the abscess is starting to open is often a dark area on the top of the lump. Most commonly, the skin on the top of the lump will die and turn dark, hard and “crunchy.” Eventually the disc of dead skin will fall off leaving a hole, often quite a large hole, leading to a pocket. This is all okay.
In most cases, the pus will drain out and the rat will lick the pocket clean, so you don’t have to do anything. The hole will usually heal up in a few days. Sometimes, the dead skin will not come off completely and will need to be cut away.
This small abscess on my hairless rat’s ear (photo #1) took quite while to open. I took the first photo on 9/25/10, and you can see the yellow pus through the thin layer of skin over the top of the lump. The next photo (photo #2) was 12/23/10. I finally got tired of waiting and squeezed it out. You can see the blob of pus that came out. The black dot on Munchkin’s shoulder (circled in blue) is a tiny sebaceous cyst.
Abscesses and Cysts
By Debbie Ducommun
Here is a series of photos I took of my rat Comet who developed a sterile abscess in his scrotum nearly 5 months after he was neutered!
Photos A and B were taken on 5-12-11, one before and one after I shaved his scrotum. You can see the dark area of dead skin that will come off.
I took the next picture (photo C) on 5-16-11, and you can see at the bottom edge of the dark area, some greenish pus starting to seep out. I took the last picture (photo D) on 5-21-11, after the dead skin had fallen off, and you can see the wound is already healing well.
Photo #3 is a sterile abscess that developed after a neuter due to a reaction to the sutures. See the dark spot where the hole will form.
Left Top Row:
3 photos of tiny new sebaceous cysts. Of course, they are much easier to see on hairless rats.
Left Bottom Row:
Here’s a little sebaceous cyst that I squeezed out, showing all the stuff that came out, and what it looked like afterwards.