Dogs and cats have two kidneys that lie within the abdomen along the spine. The kidneys are essential filters that remove toxins and wastes from the blood. They produce a hormone that stimulates the bone marrow to make red blood cells. They also maintain the correct balance of water, various salts and minerals in the body. Each kidney is connected to the urinary bladder by a ureter, a tube for transport of urine.
Two types of kidney tumors exist, those that originate in the kidney and those that have spread (metastasized) to the kidney from another tumor within the body. Tumors that originate within the kidney include renal carcinoma, renal adenocarcinomas, transitional cell carcinoma, sarcomas of varying types, and a tumor that originates from embryonic cells called a nephroblastoma. At the time of diagnosis of a kidney tumor in a dog, about 16% of them have evidence of metastasis to the lungs. In cats, the incidence of metastasis at the time of diagnosis was reported to be 64% for renal carcinomas and 100% for transitional cell carcinomas.
Certain dog breeds are more prone to develop kidney tumors: cocker spaniels, Labrador retrievers, Rottweilers, golden retrievers, German shepherds, miniature poodles, malamute, springer spaniel and Shetland sheepdogs. Males develop this tumor about 50% more frequently than females and the average age of affected pets is 8.4 years. Patients with nephroblastomas tend to be much younger. Most common clinical signs in affected patients include bloody urine, a palpable abdominal mass, increased thirst, increased urination, lethargy, weight loss, vomiting, pain and behavioral changes.
The diagnosis of a kidney mass is made from abdominal X-rays or abdominal ultrasound. Advanced imaging such as an abdominal MRI or CT scan can be used to define the extent of the kidney tumor but also may be used to determine if visible metastasis is present. Chest X-rays are used to identify visible spread of the cancer; however, microscopic spread of the tumor to other organs cannot be detected with X-rays. Blood work and urine testing is done to ensure that the unaffected kidney is functioning normally and other internal organs are healthy.
Nephrectomy, or surgical removal of a kidney, is the best treatment for a kidney tumor, providing that the patient is not in kidney failure. An incision is made along the abdomen to expose the internal organs. The blood vessels and ureters of the affected kidney are tied off, and the kidney is then removed.
While in the hospital, your companion will continue to receive intravenous fluids, electrolytes and in some cases plasma or an artificial plasma product called hetastarch. Uncommonly, a blood transfusion may be necessary. Your companion will be carefully monitored in the intensive care unit and given narcotics to ensure a pain-free recovery. Most patients that have abdominal surgery leave the hospital within 24 to 72 hours.
In a study, which included 82 dogs, the average survival time following nephrectomy was 16 months, regardless of tumor type. Patients that received follow-up chemotherapy survived a few months longer than patients receiving only surgery; however, this was not found to be statistically significant. At the time of death of affected patients, 77% had evidence of metastasis. Because the evidence of metastasis at diagnosis is greater in cats, the prognosis may be poorer for cats than dogs.
For more information on this subject, speak to the veterinarian who is treating your pet.