Cysts in Cats: Skin, Belly, Kidney, and Leg Lumps

Name: Cysts in Cats: Skin, Belly, Kidney, and Leg Lumps
Creator: Dr. Zubair Khalid

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-10-03

Cysts in cats skin are fluid-filled sacs that form under or within the skin, and most turn out to be harmless. They can also appear on the belly, legs, and inside the kidneys, where they range from minor findings to serious inherited disease. The sections below explain what each type looks like, how your vet tells a cyst from a tumor, and when watching is safe versus when removal is best.

This article is educational and is not a substitute for veterinary diagnosis or treatment.

Quick Answer

A cyst is a pocket of fluid, keratin, or hair enclosed in a lining. A tumor is a growth of cells. You cannot reliably tell them apart by look or feel alone.
Dermoid cysts, the most common developmental skin cyst in cats, average about 1.4 cm across and appear most often on the neck along the top midline [1].
A cyst on the belly or leg is usually a skin or adnexal cyst, but abdominal cysts can also arise from the liver or other organs and need imaging to identify [2].
Kidney cysts in cats may be harmless, or they may be part of polycystic kidney disease, a hereditary condition that slowly reduces kidney function [3].
Any new lump that grows quickly, changes color, bleeds, or bothers your cat should be examined by a veterinarian, usually within days, not months.

What Cysts in Cats Skin and Other Areas Actually Are

A cyst is a closed sac with a lining of its own. The lining makes a substance, usually fluid, keratin, or a mix of both, and the sac holds it in. That structure is what separates a cyst from a solid mass. A tumor is made of multiplying cells, and it has no manufactured cavity unless it dies off in the middle.

Dermoid cysts are a specific type. They are developmental abnormalities, meaning the cat is born with them. They form along the dorsal body midline and histologically reduplicate the skin, containing collagen bundles, adnexal structures, and a filling of keratin and hairs [1]. In other words, a piece of skin got trapped in the wrong layer during development and kept making skin products.

Cysts elsewhere follow the same basic rule but start from different tissue. A cyst in the liver can be a benign biliary tumor called a hepatobiliary cystadenoma, which forms a multiloculated pocket with thin septa [2]. A cyst-like lesion around the kidney can be a pocket of inflammatory fluid instead of a true lined cyst [4]. In the brain, some meningiomas in cats carry a pseudocystic fluid component, meaning the fluid collects next to the tumor instead of inside a true cyst wall [5].

Signs Owners Notice: Cysts in Cats Symptoms

Most skin cysts announce themselves as a lump you feel while petting your cat. They are often round, smooth, and movable under the skin. Dermoid cysts in cats are usually cutaneous or subcutaneous, and most cause no inflammation at all, so the skin over them looks normal [1].

A cat cyst on the belly may be harder to spot because of fur and posture. You might notice it during grooming or when your cat rolls over. Some are found only when a vet palpates the abdomen during a routine exam.

Kidney cysts are almost always invisible from the outside. In a cat with polycystic kidney disease, the cysts grow silently while kidney function declines. An 18-month study of affected cats documented a 14 percent increase in cyst volume, a 7 percent enlargement in kidney length, and rising creatinine, phosphorus, and blood urea nitrogen levels as the disease progressed [3]. Progressive anemia also appeared as chronic kidney disease advanced [3]. Those changes show up on bloodwork and ultrasound long before you would see anything at home.

When kidney or liver cysts become massive, signs turn outward. A cat with a giant hepatobiliary cystadenoma had several weeks of vomiting, inappetence, and abdominal distension, plus a cholestatic pattern on bloodwork with elevated alkaline phosphatase and gamma-glutamyl transferase [2]. A Persian Chinchilla cat with polycystic kidney and liver disease developed lethargy, right hindlimb pain, and lameness from a rare circulatory complication [6].

A cyst in a cat's leg may cause limping if it presses on muscle, tendon, or nerve. More often it is a cosmetic lump. Size and location matter more than the word "cyst" when it comes to symptoms.

Causes and Risk Factors

Dermoid cysts are present from birth but often noticed later. In a series of 220 cases, the average age at diagnosis was 5.5 years, and 59.5 percent were male [1]. Domestic shorthairs made up 56.4 percent of cases, which likely reflects how common the breed is instead of a true predisposition [1]. The neck was the most common location, accounting for 55.9 percent of cysts, and one cyst sat in the mesentery instead of the skin [1].

Polycystic kidney disease is inherited. It has been tied to a known pathogenic mutation in the PKD1 gene, and a cat in one report also carried a frameshift mutation in GANAB plus missense variants in PKD1 and PKHD1 [6]. Persian and Persian-related breeds are classically affected, and the cat in that report was a Persian Chinchilla [6].

Breed can also drive cyst-like skin disease. Lykoi cats carry variants of the Hairless gene, and a prospective study of 10 affected cats found a comedonal syndrome with infundibular follicular cysts on biopsy [7]. Cats ranged from 1.5 to 7 years old at diagnosis, and involvement ranged from severe generalized disease to mild scattered lesions [7].

Some cyst-like lesions are not genetic at all. Perirenal cyst-like lesions around the kidneys have been reported in a cat with feline infectious peritonitis, where the pockets were tied to pyogranulomatous inflammation instead of a developmental defect [4]. That is a reminder that "cyst" on an ultrasound report describes an appearance, not always a single disease.

How Vets Tell a Cyst From a Tumor

Your vet starts with hands and history, then uses sampling. A fine needle aspirate pulls cells and fluid from the lump. Cytology can often separate a cyst's watery or keratin-rich contents from the cells of a tumor. Solid masses, unusual cells, or blood-tinged fluid push the workup further.

Imaging answers the location question. Ultrasound is the main tool for abdominal cysts, and it can show whether a structure is a simple fluid pocket, a multiloculated cyst with septa, or a mass with solid components [2]. For a suspected liver cyst, contrast-enhanced computed tomography confirmed a 163 by 148 by 136 mm cystic hepatic mass with homogeneous fluid attenuation, non-enhancing septa, and no solid components [2]. That combination of features pointed toward a benign cystadenoma, though histopathology after surgery was still required to confirm it [2].

Bloodwork matters when cysts sit in organs. A cat with kidney or liver cysts needs creatinine, phosphorus, blood urea nitrogen, and a complete blood count to check for the anemia and azotemia that accompany progressive disease [3]. Routine sonographic evaluation alongside hematologic and biochemical testing is recommended to catch polycystic kidney disease early [3].

Sometimes the answer only comes after removal. Hepatobiliary cystadenoma can mimic cystadenocarcinoma on imaging, and histopathological examination is required for confirmation [2]. If your vet recommends surgery for an abdominal cyst, part of the goal is getting that definitive diagnosis.

For a deeper look at how vets sort benign lumps from concerning ones, see Cat Skin Bumps and Lumps: When to See a Vet and When to Monitor and Decoding the Cytology of Canine and Feline Cutaneous Masses.

Cyst Versus Tumor at a Glance

Feature	Cyst	Tumor
What it is	Fluid, keratin, or hair inside a lining	Solid growth of cells
Typical feel	Smooth, round, movable	Variable, can be fixed or irregular
Growth speed	Often slow or static	Often progressive
Aspirate result	Fluid, keratin, few cells	Cells, sometimes atypical
Imaging look	Fluid attenuation, thin septa, no solid parts [2]	Solid components, enhancement, nodules
Confirmation	Cytology, imaging, sometimes histopathology	Cytology, biopsy, histopathology

Treatment Options

Small skin cysts that cause no trouble are often monitored. Your vet may measure and photograph the lump, then recheck it in a few months. If it stays the same size and your cat is comfortable, watching is reasonable.

Removal is the standard fix when a cyst grows, ruptures, gets infected, or sits somewhere that interferes with movement. Dermoid cysts are treated by surgical excision, and because they are developmental, they do not come back once the whole lining is out. Most dermoid cysts in cats are small, averaging 1.4 cm, so the surgery is usually straightforward [1].

Abdominal cysts are a bigger decision. A giant hepatobiliary cystadenoma required complete excision with preservation of hepatic tissue and biliary reconstruction [2]. That is major surgery, and it is reserved for cysts that are large, symptomatic, or suspicious for cancer. Your vet will weigh the cat's age, kidney values, and overall health before recommending it.

Kidney cysts from polycystic disease are not removed. Treatment focuses on managing chronic kidney disease with diet, hydration support, blood pressure control, and regular monitoring. In one report, a cat with polycystic kidney and liver disease and a Budd-Chiari-like complication received supportive care but died of renal failure within 7 weeks [6]. That outcome reflects how serious advanced polycystic disease can be, not how most early cases behave.

Brain cysts tied to meningiomas are handled by removing the tumor. Four cats with pseudocystic fluid accumulation underwent mass removal through craniotomy and were discharged from the hospital, and all improved neurologically after surgery [5]. Follow-up MRI six months later in two cats showed focal meningeal thickening [5].

No drug dissolves a cyst. If anyone offers a pill or supplement that "shrinks cysts," ask for the evidence. Your vet calculates any medication dose from your cat's weight and current health, and dosing for kidney or liver disease is often adjusted.

Recovery, Outlook, and Long-Term Management

After skin cyst removal, most cats heal well with a short course of pain medication and a cone if needed. Keep the incision clean and check it daily for swelling, discharge, or opening. Call your vet if the site looks angry or your cat stops eating.

Prognosis depends on where the cyst is and what caused it. A solitary dermoid cyst removed completely has an excellent outlook because the cause is gone. A benign liver cystadenoma removed with clean margins also carries a good prognosis, though the surgery itself is demanding [2].

Polycystic kidney disease is progressive. Even with diligent care from owners and veterinarians, kidney function continues to decline over time [3]. Long-term management means routine ultrasound plus blood and urine testing to track cyst volume, kidney size, and kidney values [3]. Early detection gives you more room to slow the decline with diet and supportive care.

If your cat has kidney cysts, ask your vet about monitoring for stones and other urinary complications. Kidney Stones in Cats: Diagnosing Nephroliths and Ureteroliths covers that side of kidney care. For what the imaging actually shows, Abdominal Ultrasound in Cats: Normal Findings and Common Abnormalities walks through the pictures your vet reads.

Prevention

You cannot prevent a developmental cyst. Dermoid cysts form before birth, so there is no diet, shampoo, or supplement that stops them [1].

You can reduce the impact of inherited disease. If you are buying a kitten from a breed with polycystic kidney disease in its background, ask about genetic testing of the parents. A known pathogenic PKD1 mutation has been identified in an affected cat, and DNA testing can flag carriers before breeding [6].

For Lykoi cats, the skin syndrome is tied to the breed's Hairless gene variants, so it is not something you can prevent with grooming [7]. You can manage it by keeping the skin clean, treating secondary infections promptly, and having new bumps checked.

The most useful prevention is early detection. Weigh your cat monthly, feel for new lumps during petting, and keep up with wellness exams. Catching a cyst while it is small gives you and your vet more choices.

Limitations and When to Contact a Veterinarian

No article can examine your cat. A lump that feels like a cyst to you may be something else, and only a veterinarian can tell the difference with hands, a needle, and imaging. Individual cases need a veterinarian's assessment.

Contact your vet the same day if a lump suddenly doubles in size, starts bleeding or oozing, smells bad, or your cat licks or chews at it constantly. A cyst in a cat's leg that causes limping also deserves a same-day call.

Go to an emergency clinic now if your cat is struggling to breathe, collapses, has a swollen painful abdomen, strains to urinate, or cannot walk on a limb. A cat with known kidney cysts that stops eating, vomits repeatedly, or seems weak may be in kidney failure and needs urgent care.

Schedule a routine visit within a week or two for any new lump, any lump that has changed, or any lump you are unsure about. Bring notes on when you first noticed it and whether it has grown. If your cat has polycystic kidney disease, keep every scheduled recheck, because the disease moves even when your cat seems fine [3].

Frequently Asked Questions

Are cysts in cats skin dangerous?

Most skin cysts in cats are benign and cause no harm beyond a cosmetic bump. The danger is misjudging a tumor as a cyst, which is why a vet exam and often a needle sample are needed. Once a cyst is confirmed, the main concerns are growth, rupture, and infection.

Can a cat cyst on the belly go away on its own?

Some small cysts stay the same size for years, and a few may shrink if the contents drain internally. They rarely disappear completely because the lining remains. If a belly lump is growing or your cat seems uncomfortable, have it checked instead of waiting.

Do cysts in cats kidneys always mean kidney disease?

No. A single simple kidney cyst can be an incidental finding that never causes problems. Polycystic kidney disease is different because cysts form throughout both kidneys and progressively reduce function over time. Ultrasound and bloodwork together tell your vet which situation you are facing.

Will my vet remove a cyst in my cat's leg?

It depends on size, location, and symptoms. A small cyst that does not affect walking is often monitored. A cyst that causes limping, grows quickly, or sits near a joint or nerve is more likely to be removed.

Can I pop a cyst on my cat at home?

Never. Squeezing or lancing a lump can cause infection, bleeding, and pain, and it can spread tumor cells if the mass is not a cyst. Let your vet decide whether drainage or surgical removal is appropriate.

References

Feline dermoid cyst: Retrospective case series and literature review. Veterinary pathology, 2025.
Giant Hepatobiliary Cystadenoma Requiring Biliary Reconstruction in a Cat: A Case Report. Veterinary medicine and science, 2026.
Contribution of polycystic kidney disease to the development of chronic renal dysfunction in cats. Veterinary research forum : an international quarterly journal, 2026.
Perirenal cyst-like lesions associated with feline infectious peritonitis in a Maine Coon cat. JFMS open reports, 2025.
EXPRESS: Meningiomas in four cats with pseudocystic fluid accumulation including one microcystic meningioma. Journal of feline medicine and surgery, 2026.
Case Report: Budd-Chiari-like syndrome in a cat with polycystic kidney and liver disease. Frontiers in veterinary science, 2025.
Clinical, histopathological and genetic features of a cutaneous adnexal polycystic syndrome in Lykoi cats: a prospective study of 10 cases. Journal of feline medicine and surgery, 2026.