The veterinarian palpates (feels) your cat’s abdomen during a clinical exam and finds that one or both of her kidneys are bigger than they’re supposed to be. It happens more frequently than you might expect. The medical term for enlarged kidneys is renomegaly, “reno” meaning “kidneys” and “mega” meaning “large.” But the finding is not a diagnosis in itself. It’s a clue that a diagnosis is necessary, and it’s sometimes accompanied by other clues, such as decreased appetite, weight loss, lethargy, and vomiting.
Tests are going to have to be ordered: perhaps blood and urine screenings, x-rays, and ultrasound. Maybe a fine-needle aspirate will be conducted to pull some cells from the kidneys with a syringe and exam them under a microscope. In some cases, a biopsy will be in order.
In the meantime, whether one or both kidneys are affected and how they feel to the doctor can potentially give some ideas about what disease she might be looking for. Here’s a rundown of what a vet might feel as she presses on your pet’s abdomen.
Both kidneys enlarged and painful to the cat. Acute kidney injury may present this way. The kidneys will feel smooth and swollen to the vet as she gets at the abdomen from the outside. Common causes include ingestion of toxins like antifreeze or a bacterial infection of the kidneys. This is not like chronic kidney disease that keeps progressing. Once the cause of the acute kidney injury is treated, kidney function may be able to return to normal.
Moderate to severe enlargement of both kidneys. This could be a sign of the most common cancer to affect the feline kidneys: lymphoma.
The lymphoma causes the kidney disease, which leads to poor appetite, weight loss, excessive thirst and urination, lethargy, and pale gums. The doctor will often find that lymphoma has affected other organs as well — which makes sense since the lymph system runs throughout the body (parallel to the blood vessels), taking white blood cells to tissues and removing waste. About half of cats with lymphoma also have feline leukemia virus.
Enlarged, irregularly shaped kidneys. If the doctor feels the kidneys are not the shape they are supposed to be while at the same time too big, she might suspect feline infectious peritonitis (FIP). There are two forms of this deadly viral disease. With the “wet” form, a cat’s abdomen (and sometimes her chest cavity) fills with fluid. With the “dry” form, clusters of inflammatory cells called granulomas infiltrate various body organs, including the kidneys. It’s the dry form the doctor will feel. The granulomas will throw off the kidneys’ shape.
Enlarged and irregularly shaped kidneys could also indicate polycystic kidney disease. It’s an inherited disorder in Persian cats and Persian mixed breeds in which normal kidney tissue is replaced with multiple enlarging cysts. Other signs, including loss of appetite and excess drinking and urination, often do not appear until the disease is far along.
One kidney too large, one too small. Sometimes a cat suffers some kind of damage in one of her kidneys that results in loss of function there. The kidney tissue grows smaller, and scar tissue forms. To compensate, the still-healthy kidney grows somewhat larger. It’s called compensatory hypertrophy. Cats, like people, can do quite well with one kidney.
Less common causes of enlarged kidneys
There are a number of other possible reasons for renomegaly in a cat that occur more rarely. Among them is primary renal cancer, which is a malignancy that directly affects the kidneys rather than the lymphatic system that goes past them. It comprises less than 2 percent of all feline cancers.
A renal abscess in a single kidney is another possible cause of enlargement. An abscess is a pocket of pus that develops for one reason or another, often an infection. A cat may exhibit pain upon palpation if an abscess is present.
A hematoma can cause kidney enlargement, too. A solid swelling composed of clotted blood, it usually forms in response to abdominal trauma or a penetrating wound.
An obstruction in the flow of urine is yet another reason that one or both kidneys might enlarge. Urine builds up in the kidney(s) because it can’t make its way out, perhaps because of the development of kidney stones or a stricture in one or both ureters that lead away from the kidneys. The medical term for this complication is hydronephrosis, and it might make the kidneys particularly large.
Age and other factors
A cat’s age can help a veterinarian make decisions about what disease she might be looking for as a result of finding enlarged kidneys upon clinical examination. If it’s an older cat, she’s going to be more likely to suspect cancer. If the cat is still young, she may consider FIP or wonder if the pet accidentally ingested a poison. She might also ask if the cat got into a scrape with another animal, which could potentially point to a hematoma. And, of course, if your pet is a Persian or Persian mix, she might suspect polycystic kidney disease.
Note that abnormally large or irregularly shaped kidneys felt by the doctor upon examination are not always the first sign that something is wrong. Sometimes a routine blood or urine test will come back abnormal and indicate that something is up. Other times, the tip-off will be found by you at home in noticing that your cat does not seem her usually peppy self and/or is quite thirsty and relieving herself much more often than usual in the litterbox (or outside of it). But palpating the feline abdomen to feel for kidney size and shape is an important tool in the diagnostic arsenal.
