My pet rat has a swollen cheek?

There are many things that could be wrong with your rat. The face is a delicate area and many lumps/abnormalities could be related to dental problems. Be sure to have the vet check your rat's teeth, and see if your rat is having any issues eating. It could also be a tumor or abscess. A tumor is a growth that very rarely goes away on it's own. Most of the time they are benign, and rats can continue to live happily even with a tumor. An abscess is a big puss-filled sack. Rats often get them due to an injury or bite from another rat. Having one on the face is dangerous because it is so close to the eyes, but rats often make a very healthy recovery if it is drained properly.