Congenital and Inherited Disorders of the Urinary System in Dogs
Certain urinary tract abnormalities are inherited or congenital (present at birth). These abnormalities are caused by abnormal genes or produced by injury, disease, or exposure to toxic substances in the womb. They may or may not cause health problems later in your pet’s life. They are rare, but important to consider, if your dog has urinary tract problems.
There are many congenital and inherited problems that can affect the kidneys. Among these are kidney malformations, failure of the kidney(s) to develop, polycystic kidneys, and kidney cysts.
Kidney malformations, called dysplasias, occur when a dog’s kidneys do not develop properly before birth. When the kidneys are unusually small, the condition is called hypoplasia. These conditions have been reported in many breeds, including Alaskan Malamutes, Bedlington Terriers, Chow Chows, Cocker Spaniels, Doberman Pinschers, Keeshonden, Lhasa Apsos, Miniature Schnauzers, Norwegian Elkhounds, Samoyeds, Shih Tzus, Soft-coated Wheaten Terriers, and Standard Poodles. Dysplasia can occur in either one or both kidneys. When these conditions occur, the kidneys are usually small, firm, and pale. The outer portion of the kidney that contains glomeruli (microscopic structures which are critical for filtering blood) may be smaller than normal in size.
Dogs with these conditions typically have a buildup in the blood of the toxic waste products that are normally excreted in the urine, which becomes evident between 6 months and 2 years of age. Before this occurs, however, an affected dog usually has ongoing, excessive thirst (called polydipsia) and corresponding excessive urination (polyuria). A dog whose kidneys start to fail in the first few months of life will also show signs of stunted growth. Your veterinarian can usually diagnose dysplasia or hypoplasia based on your dog’s breed, the age it begins to show signs of disease, and blood and urine tests. The diagnosis can be confirmed with a biopsy of the kidneys.
There is no treatment for renal dysplasia or hypoplasia. Care for affected dogs consists of managing the problems associated with the kidney failure that results from these conditions.
Rarely, one or both kidneys fail to develop. This condition is always accompanied by a lack of the tube connecting the kidney to the bladder (ureter). The reproductive organs may also be underdeveloped. A dog in which both kidneys have failed to develop will die shortly after birth. However, an animal with one functioning kidney can live a full and healthy life. In this case, the failure of one kidney to develop is usually discovered by accident. The condition is more likely to occur in some breeds, such as Beagles, Shetland Sheepdogs, and Doberman Pinschers.
Polycystic kidneys have multiple cysts inside the functional part of the organ. Affected dogs may also have cysts present in the liver. The kidneys are greatly enlarged, which a veterinarian may be able to feel during a physical examination. Problems caused by this condition can range from none at all to progressive kidney failure. In dogs, this condition is inherited in Beagles, Bull Terriers, West Highland White Terriers, and Cairn Terriers. Your veterinarian can diagnose polycystic kidneys by examining your pet, taking x-rays, using ultrasonography, or performing exploratory abdominal surgery.
About 5% of dogs have 2 or more renal arteries. A normal kidney has 1 renal artery, which delivers blood to the kidneys. Other congenital problems include kidneys that are not positioned correctly, kidneys that are fused together, and nephroblastoma, a cancer that develops in the kidneys as a result of abnormal kidney tissue growth in the womb.
Several disorders can affect the ureter, the tube that connects the kidney to the bladder. Normal animals have 2 ureters, 1 for each kidney.
An ectopic ureter is one that opens somewhere other than into the bladder. Ectopic ureters could empty urine into the urethra (the tube used for urination), or in females, the uterus or vagina. This defect is most commonly identified in 3- to 6-month-old dogs, with females affected 8 times more frequently than males.
Other problems can occur along with an ectopic ureter. An enlarged ureter caused by blockage of urine flow may be seen. This condition eventually leads to enlargement of the kidney due to the backup of urine. Abnormally small kidneys or bladder, and urine leakage caused by problems with the urethral sphincter may also be found along with an ectopic ureter.
A common sign of ectopic ureter is continuous dripping of urine. Because urine that remains on skin or other tissues is irritating, this dripping can cause female dogs to develop inflammation of the vagina or vulva. Animals that have one ectopic ureter and one normally-functioning ureter may be able to urinate normally. Not being able to urinate normally is a sign that both ureters are abnormally placed.
West Highland White Terriers, Fox Terriers, and Miniature and Toy Poodles are at high risk for this condition. Siberian Huskies and Labrador Retrievers are also at a somewhat higher than normal risk. Your veterinarian can diagnose this condition using x-rays taken after a special dye is given intravenously.
Ectopic ureters can be treated by surgically moving the ureter to the correct place, or, in severe cases, removing the affected ureter and the accompanying kidney. Some dogs will still leak urine after surgery, but medications can minimize this.
The bladder is a muscular sac that stores urine produced by the kidneys. Several congenital and inherited problems can affect the bladder.
The urachus is a cord of fibrous tissue that normally extends from the bladder to the navel. Before birth, the urachus is a tube that connects the bladder to the umbilical cord so that wastes can be removed. After birth, it normally closes and becomes a solid cord. In some animals, however, the urachus does not close properly after birth. Depending on which portion of the urachus remains open, these abnormalities are called a patent urachus or an umbilical urachal sinus. Other problems include urachal diverticula (small sac-like structures attached to the urachus) and urachal cysts. Signs include an inability to control urination, urine scalding (due to the fact that urine is caustic) of the skin near the navel, and urinary tract infections. Your veterinarian can diagnose these problems using x-rays taken after a special dye is placed into the bladder. Treatment usually includes surgery and, sometimes, antibiotics.
Other congenital bladder conditions in dogs include the presence of more than one bladder, an abnormally developed or underdeveloped bladder, failure of the bladder to develop, and a bladder that is turned inside-out. Usually these problems occur along with other abnormalities in the urinary tract. Your veterinarian can diagnose these problems based on a physical examination, observation of your dog while it urinates, and contrast x-rays. Treatment varies depending on the type of problem. Your veterinarian will advise you about the most appropriate treatment for your pet.
The urethra connects the bladder to the exterior of the body. It is the tube through which urine passes when a dog urinates. Congenital urethral problems in dogs are uncommon. Some of the conditions that occur include a urethra that does not open all the way or does not open at all, hypospadias (see below), multiple urethras, urethral diverticula (small pouches that form in the urethra), urethrorectal and rectovaginal fistulas (see below), and narrowing of the urethra.
In hypospadias, a condition of male dogs, the opening of the urethra occurs before the tip of the penis. In addition, the penis or testicles may not be fully developed. Hypospadias is caused by abnormal development of the fetus in the womb. Boston Terriers have an increased risk of developing the condition, suggesting it might be genetic. The signs vary depending on where the urethral opening is located. They can include urine scalding (because urine is caustic) and urinary tract infections. This condition can be treated with surgery.
Dogs with a urethrorectal fistula have an abnormal opening between the urethra and the rectum. Rectovaginal fistulas are abnormal openings between the vagina and rectum. They are more common in English Bulldogs than any other breed. Dogs with these fistulas are prone to urinary tract infections. Signs of this condition are the same signs found in urinary tract infections and include blood in the urine and painful or difficult urination. Animals with this condition may also pass urine from the rectum while urinating. This condition can be corrected by surgery. Antibiotics may be necessary to treat urinary tract infections.
Also see professional content regarding congenital and inherited disorders of the urinary system.