TL;DR: A soft, fluid-filled lump on your cat is often a benign cyst or seroma and is typically not an emergency if your pet is acting normally. Monitor the area for changes and take photos to help your veterinarian provide an accurate diagnosis during a routine appointment.
What are the common causes of a soft, fluid-filled lump on my cat?
Finding a soft, fluid-filled lump on your cat can be worrying, but many of these growths are benign. Common possibilities include a sebaceous cyst, which is a blocked oil gland, or a seroma, which is a collection of sterile fluid often following a minor bump or surgical procedure. Because these feel squishy or fluctuant, they typically contain liquid rather than solid tissue.
How urgent is a soft lump on my cat’s side?
- Schedule a routine veterinary appointment if your cat is acting normally, eating well, and the area isn't painful, hot to the touch, or rapidly changing.
- Seek care more promptly if the lump ruptures, begins to drain foul-smelling fluid, or if your cat becomes lethargic.
How does taking photos of the lump help my veterinarian with triage?
- A visual record allows the team to assess the exact location, size, and the appearance of the skin over the lump.
- Tracking photos over a few days helps determine if the mass is growing, shrinking, or changing in texture.
- Clear images provide vital information for an accurate diagnosis during your veterinary visit.
Clinical Context (Merck Veterinary Manual)
In cats, a soft, fluid-filled lump on the side may indicate a perirenal pseudocyst, which is an accumulation of fluid external to the renal parenchyma. Abdominal palpation may reveal a large, firm, non-painful mass located in the area of the kidneys. While renal function tests and urinalysis are typically normal, further investigation is warranted. Coelomic palpation may also detect other abnormalities such as retained egg masses, bladder stones, foreign bodies, or neoplasms. Hydrocoelom and subcutaneous edema (anasarca and ascites) should also be considered, as they can be caused by a variety of factors, including cardiac, renal, GI, or hepatic disease. Collection of fluid for biochemical analysis, cytologic evaluation, and culture for bacteria and fungi is recommended to aid in diagnosis.
Chapter: Urology, Diagnostic Imaging
Source: The Merck Veterinary Manual, 11th Edition (Page 1497)