My veterinarian detected renomegaly of my twelve-year old cat's right kidney. The doctor has scheduled some tests. What is renomegaly and how is it treated?
Renomegaly is enlargement of one or both kidneys. It is not a disease, but rather signals the presence of an underlying disease process. Your veterinarian has scheduled tests to determine the cause of your cat's enlarged kidney.
There are many conditions that cause renomegaly. Inflammatory conditions, kidney infection and tumors can cause the kidney to enlarge. Blockage of the urinary tract, development of kidney cysts and acute tubular necrosis (death of the filtering cells of the kidney) will also cause palpable enlargement of one or both kidneys.
Infections associated with renomegaly include feline infectious peritonitis (a viral infection), leptospirosis (a bacterial infection) in dogs, and local abscesses. The infective organisms enter kidney cells; the affected animal's inflammatory response to the infection enlarges the kidney.
Tumors such as lymphoma, renal carcinoma, Wilm's tumor (a congenital kidney mass) and certain others may affect the kidney and cause renal enlargement. One or both kidneys may be affected, depending on the tumor type.
Urinary tract obstruction may occur as a result of various types of bladder and urinary tract stones. Obstruction may lead to hydonephrosis, or urinary back up, which can cause renomegaly. Cyst formation in one or both kidneys can cause blockage and renomegaly as well. Polycystic kidney disease is an inherited congenital problem in the Persian breed that may cause substantial kidney enlargement over time. The Abyssinian breed is predisposed to amyloidosis, a condition associated with infiltration and enlargement of the kidneys.
Dogs and cats with renomegaly may show a variety of nonspecific clinical signs. These include lethargy, loss of weight and appetite, abdominal pain or swelling, vomiting and diarrhea, excessive thirst and urination, and discoloration of the urine. Pale mucous membranes, ulcers and erosions of the oral cavity, and bad breath may be present as signs of kidney failure.
The diagnostic tests employed to determine the underlying cause of renomegaly include a complete blood count, blood chemistry and urinalysis. Radiographs (x-rays) and possibly ultrasound imaging help determine not only the size dimensions of the kidneys, but will also reveal tumors and cysts if present. Dye studies of the kidney are occasionally performed. A fine-needle aspirate test, where a small needle is inserted into the kidney and a sample of cells is withdrawn, or a surgical biopsy will be performed if tissue samples are needed for histopathological (microscopic) examination. Additionally, affected cats will likely be tested for the feline leukemia virus, which causes an infection sometimes associated with renomegaly and predisposes cats to renal lymphosarcoma.
Treatment is directed toward the underlying condition. Prognosis for treatment success and recovery depend on the cause of the renomegaly. In some cases azotemia (excess ammonia-like toxins in the blood) develops if the kidneys fail. In these cases collateral treatment of the renal failure and the associated azotemia will also be necessary.
12/07/00
