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My Cat’s Cyst Keeps Filling Up, What’s Wrong? (Vet Answer)

vet checking cat
Image Credit: Lee Charlie, Shutterstock
Last Updated on December 6, 2023 by Catster Editorial Team

What Causes Cat Cysts to Fill With Fluid?

Hello Dr. Barchas,

I have an almost 17-year-old cat who has a benign basal cell cyst on his neck that I empty with a disposable needle every three or four days. I purchase them from the pharmacy and use a fresh one each time. I decided to go this route
because of his age and not wanting to subject him to surgery or invasive procedures. He allows me to do this without protesting in any way!

I understand that these cysts are common in elderly
cats and are found mainly around the neck area, but I can see a tiny one just beginning above his right eye.

What I am wondering is what exactly is the fluid in the cyst and why does it fill up faster some days than others? I emptied it yesterday and already it is half full , yet the
last time I did it it took nearly five days to be completely full.

He is healthy otherwise, eating and his normal self—he does show signs of aging however and I want to make absolutely certain he is as comfortable and stress-free as
possible. Thanks so much for any advice you can give.

London, ON, Canada

Vet Answer

Cysts are generally harmless growths that occur in the tissues of animals. They are common in older pets (although they sometimes develop in young pets), and they are encountered most frequently in the skin (although they can occur in other tissues as well).

Cysts are made of cells that involute to form a sac, or empty cavity. In some cases, the cells that make up the cyst secrete fluid into the sac. In others, the cyst incites the immune system to secrete fluid. In either case, the result is essentially the same: a bag of cells with fluid inside of it.

The rate at which fluid enters the cyst depends on a number of factors. Cysts that are irritated, traumatized, inflamed or in areas of high motion may fill faster than other cysts. In many cases, cysts seem to have a mind of their own: after one draining, a cyst may remain empty for months or years. After another, it could be full again the next day.

In many cases it is not necessary to drain cysts. In fact, I only recommend draining if the cyst is causing pain, irritation, or some other sort of trouble. Regardless of whether or not a cyst is drained, it may become irritated or infected. It also may burst or change into a more dangerous type of growth.

Keep a close eye on your pet’s cysts, and have a vet check him out if you notice any major changes. Also, if you have not already done so, have a vet check the new growth above your cat’s eye to ensure that it is, in fact, another cyst and not something more serious.

As long as you confirm that neither growth is dangerous, I see no reason to remove them. They should not interfere with your pet’s longevity or quality of life.

Feature Image Credit: Lee Charlie, Shutterstock

About the Author

Dr. Eric Barchas
Dr. Eric Barchas

Dr. Eric Barchas is a professional traveler who spends his spare time working as a full-time veterinarian; contributing to Dogster and Catster; walking, cooking, camping, and exploring the outdoors; skiing (when conditions permit); and reading Booker-shortlisted novels. In between trips Dr. Barchas lives and works in the San Francisco Bay Area with his wife, Denise, and his canine pal, Buster. His main veterinary interests are emergency and critical care, wellness, pain management and promotion of the human-animal bond. Dr. Barchas has to Dogster and Catster since May 2005. 

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