Q: My 15-year-old female domestic cat, Buffy, has a “fatty” cyst on her back left leg just below her “hock” joint. The cyst is about 1 inch in diameter and popped up two days after my cat’s yearly rabies and distemper vaccines. My vet said these shots were not given on her back leg, however, she also received a Benadryl shot by a tech — where, we don’t know.
How likely is it that the cyst is a result of the Benadryl shot? My cat vet said he researched the connection and found that the cyst is likely a “red herring” or coincidental and not related to any of her shots. The biopsy of the cyst shows is it not malignant, but fatty tissue. My cat’s vet also told me the cyst should be removed, as it could grow.
Should I have the cyst removed? My cat has had some minor kidney problems, but has improved from 40 to 50% functioning.
A: I have a feeling that this cat “cyst” is actually a lipoma — a benign lump of subcutaneous (under the skin) fatty tissue that can develop in any cat, anywhere on their body, for no known reason.
I doubt that this lipoma “popped up” two days after her vaccinations. More likely, you just happened to notice it coincidentally two days after her vaccination and didn’t realize that it had been there for a while.
Some cats develop lumps at vaccine injection sites, and these can be worrisome, however, this is not the case with your cat, because vaccines are never given below the hock joint.
Giving a Benadryl shot at the time that the cat’s vaccines are given is not routinely done, unless a cat has a history of having an adverse reaction to vaccines in the past. Regardless, a Benadryl injection would never be given below the hock, and would not cause a lipoma at the injection site.
Was your cat’s lipoma actually biopsied, or was it simply aspirated? Most veterinarians diagnose lipomas by inserting a needle into the mass, aspirating some of the contents of the mass into the hub of the needle with a syringe, and then squirting the sample onto a slide. The slide is then evaluated by the veterinarian, or by a pathologist. Lipomas can be diagnosed by most veterinarians themselves; the aspirated contents, when squirted out onto the slide, appear fatty or greasy. I suspect that this is what your veterinarian did.
Most lipomas do not need to be removed, as they are benign. Some, however, may need surgical removal is they are present on the body in a location that could cause problems if the lipoma grows. Many years ago, I had to remove a lipoma from the side of a dog’s leg because it had grown so large that it prevented the dog from lying down on that side. Without seeing this particular mass, I cannot say whether removal is indicated. This is something your veterinarian will have to advise you on.