(See also Overview of Urinary Tract Birth Defects.)
There are several different birth defects that affect the kidneys (the two organs that filter waste from the blood to make urine). These defects are not usually apparent at the doctor's examination and require tests to evaluate the urinary tract.
There are many types of birth defects of the kidneys. Many of these defects
Blockage of urine flow can cause urine to become stagnant and result in urinary tract infections (UTIs) or formation of kidney stones. Blockage of urine flow also can raise the pressure inside the kidneys and damage them over time. Kidney damage can cause high blood pressure and, rarely, kidney failure.
A number of birth defects may result in abnormal kidneys. Kidneys may be
In the fetus, kidneys first develop in the pelvis and then move up and rotate into their normal location in the upper abdomen. If the kidneys are in the wrong place (ectopic kidneys) or are not rotated properly (malrotation), the normal drainage of urine from the kidneys through the ureters (the tubes that transport urine from the kidneys to the bladder) to the bladder (the expandable, muscular sac that holds urine) may be blocked.
Children who have blockage that causes frequent urinary tract infections or other problems may need surgery. However, many children do not have symptoms and thus may not need surgery.
A horseshoe kidney is the most common fused kidney defect. In horseshoe kidney, the fetus's kidneys join together into a horseshoe-looking shape. Because they are joined together, the kidneys do not usually move up and rotate into their normal location and also may not develop properly. Because of these factors, a horseshoe kidney may not drain properly, increasing the risk of urinary tract infections, kidney stones, and kidney damage. However, over half of children with a horseshoe kidney never have any symptoms. Children who have a horseshoe kidney may also have other birth defects.
In some children, one or both of the kidneys may not develop at all (kidney agenesis). Children who are missing both kidneys cannot survive.
In children who are missing only one kidney, the remaining kidney usually develops normally and often becomes bigger than normal to compensate for the missing one. In such cases, the child is expected to have a normal life expectancy and does not need any treatment.
Sometimes a kidney does not form properly and may not function properly or at all (kidney dysplasia). When only one kidney functions properly, it may become bigger than normal to make up for the loss of function of the other kidney. Because all of the functions normally done by two kidneys can be carried out adequately by one healthy kidney, children who have only one functioning kidney often lead normal, healthy lives. However, if dysplasia is widespread and affects both kidneys, children may need treatment to replace the kidney function. That is, they will need a kidney transplant or dialysis (a way to remove waste products and excess fluids from the body).
Polycystic kidney disease is a hereditary disorder in which many fluid-filled sacs (cysts) form in both kidneys. The kidneys grow larger but have less functioning tissue.
There are several forms of polycystic kidney disease. One form, autosomal dominant polycystic kidney disease, does not appear until adulthood and usually causes mild symptoms.
Autosomal recessive polycystic kidney diseaseis the rare form of this disorder that begins during childhood. In this disorder, the cysts become very large and cause serious illness. A severely affected newborn may die shortly after birth because kidney failure can develop before birth, leading to poor development of the lungs. The liver is also affected, and at 5 to 10 years of age, a child with this disorder tends to develop portal hypertension, or high pressure in the blood vessels that connect the intestine and the liver (portal system). Eventually, liver failure and chronic kidney disease occur. Infants who survive the newborn period may need kidney (and sometimes liver) transplantation.
Multicystic dysplastic kidney (MCDK) disease is the most common cyst-causing disease of the kidneys in children. In MCDK disease, the kidney does not develop normally and instead has multiple fluid-filled sacs (cysts) that grow inside the kidney and take over the normal kidney tissue. The kidney does not function at all. MCDK disease typically affects only one kidney. If it affects both kidneys, the fetus dies. However, children who have only one affected kidney often have a good outlook, depending on what other abnormalities, if any, they have. Sometimes the unaffected kidney has other defects that can cause blockage of urine flow.
MCDK is usually detected during routine prenatal ultrasonography, and most children have periodic ultrasounds after birth to determine whether the unaffected kidney is functioning properly. The affected kidney almost always shrinks and disappears. If the kidney does not go away, doctors sometimes remove it later in childhood. Because the unaffected kidney usually becomes bigger over time to compensate for the affected one, children usually have normal kidney function. If children have urinary blockage that causes frequent urinary tract infections or other problems in the functioning kidney, they may need surgery.
Before birth, urinary tract defects are often discovered by doctors during routine prenatal ultrasonography or other routine screening tests for hereditary disorders.
After birth, kidney defects that cause no symptoms are often discovered when imaging studies are done for other reasons. If doctors suspect a child has a kidney defect, they typically do imaging tests such as ultrasonography, computed tomography (CT), nuclear scans, or magnetic resonance imaging (MRI). Rarely, doctors do intravenous urography.
Children who have dysplasia may undergo a biopsy of the kidney (a sample of kidney tissue is removed and examined under a microscope).
People who have polycystic kidney disease may have genetic testing done to help them understand the probability that their children will inherit the disease.