To understand this condition, it is helpful to understand how the urinary tract works. In simple terms, the kidneys filter the blood and remove waste products that are then taken out of the body in the urine. The cortex of the kidneys make the urine. This urine collects in the pelvis, which empties into a tube (the ureter) and then drains into the bladder. From the bladder, urine drains out of the body through the urethra.

During pregnancy, the placenta does most of this work for the baby. The baby's kidneys start to produce urine beginning between the 5th and 9th week. Before birth, the urine made by the kidneys contributes to the amount of amniotic fluid that surrounds the baby. The amniotic fluid is important for lung development and maturing as well as giving the baby a "cushion" and providing him or her space to move.

• Twenty to 30 percent of birth defects diagnosed prenatally (before birth) have to do with the urinary tract. 
• Unilateral (one side) multicystic dysplastic kidney (MCDK) occurs in 1 in 1,000 to 4,300 babies born. 
• MCDK occurs most commonly in Caucasian (white) babies. 
• MCDK occurs slightly more often in boys than girls. 
• When girls get MCDK, they are twice as likely to have bilateral MCDK disease (affecting both kidneys) along with other birth defects.
• Most cases of MCDK occur on one side, most often on the left side. 
• The two most common birth defects seen with MCDK (that are not related to the urinary tract) are esophageal atresia (a condition in which the esophagus, or food pipe, does not connect to the stomach) and heart problems. Esophageal atresia can be fixed with surgery. 
• Multicystic dysplasia of the kidney is the most common cause of an abdominal mass in a newborn.

Other names used to describe this condition can include multicystic kidney and multicystic renal dysplasia. The ultrasound pictures of a kidney with MDCK will show a large, echogenic (bright white) kidney with multiple cysts (fluid filled masses) of various sizes. The MCDK kidney has little or no function. 

In the past, before the routine use of ultrasound with pregnancy, these were diagnosed on physical exam after birth. However, today, about 70 percent are seen on ultrasound before the baby is born. 

Sometimes MCDK will occur on both sides (1 in 10,000 live births) or will be seen on one side with no kidney on the other side. Both of these conditions are lethal. Lethal means that the baby cannot survive after birth because there is no treatment to fix the problem. One of the biggest reasons these conditions are lethal is because the urine made by the kidneys adds to the amniotic fluid. If there are no kidneys or the kidneys do not function and make amniotic fluid, the baby's lungs will not develop. The amniotic fluid is necessary for the baby's lungs to grow and mature. However, as long as one kidney is working, there should be an enough amniotic fluid for the lungs to grow and mature. 

We do not know what causes MCDK. Experts suspect that it is the result of an early blockage. In other words, the flow of urine was blocked somewhere along its path from the kidney. 

We do know it is not caused by anything the mother did or did not do. 

Seventy percent of MCDK cases are diagnosed by ultrasound before a baby is born. When your doctor performs a routine ultrasound, he or she may suspect there is something wrong with the kidney(s) and will likely refer you to a maternal-fetal medicine specialist (a doctor who handles high-risk pregnancies). The maternal-fetal medicine specialist will confirm the diagnosis of MCDK using an ultrasound that looks specifically at your baby’s kidneys. He or she also will examine the rest of your baby's body for other birth defects.

About 50 percent of babies with MCDK will have another problem that is related to the kidneys. Most of these problems are issues with the opposite kidney and are minor, but they will require follow-up after your baby is born. 

The more common kidney issues include:

• Hydronephrosis (swelling of the baby’s pelvis) that is the result of a backflow of urine
• Blockage of the ureteropelvic junction (the area that the pelvis and ureter meet)

Other birth defects that are not related to the kidneys occur more often if both kidneys have been affected with MCDK. Your doctor may recommend a genetic test because MCDK has been associated with some syndromes and genetic disorders. A perinatologist will discuss the risks and benefits of this test with you before performing this test.

If your baby has unilateral multicystic dysplastic kidney disease and a normal, working kidney on the other side, this diagnosis should have very little effect. However, if your baby has other birth defects, there may be additional problems.

After your baby is born, the doctor(s) will examine him or her for any other issues. We will plan close follow-up care to make sure your baby stays healthy. 

About every 3 to 4 months during your baby’s first year, doctors will perform a renal ultrasound to look at the kidneys. The kidney with MCDK disease may increase in size, stay the same size or get smaller. Many of these kidneys will slowly shrink in size. 

Very rarely, a malignancy (cancerous growth) of the affected kidney occurs. Another very rare problem is hypertension (high blood pressure). 

The plan of treatment for this condition will vary from baby to baby and from doctor to doctor. In the past, before we were able to make this diagnosis before birth, many of these kidneys were removed in the operating room simply to be able to see the abdominal mass. Today, with more advanced tests (X-ray, CT scan, MRI and ultrasound), most doctors agree that the best way to care for these babies is to watch the affected kidney very closely for size changes. Your baby’s doctor also will closely watch the other kidney for its ability to make urine.

Tests

If your baby has MCDK, he or she will have to undergo some testing, including:

• Renal ultrasound: Doctors will perform a renal ultrasound at 4 to 6 weeks and again at 6 to 9 months to look at the kidneys.
• Voiding cystourethrogram: Your baby’s doctor may also perform another test called a voiding cystourethrogram. This is a special X-ray that watches the kidney as it makes urine and watches the filling and emptying of the bladder and whether there is backward flow of urine. 
• Additional tests: The doctor may also recommend additional tests.

The pediatric urologist (a doctor who specializes in treating urinary tract issues in children) will discuss these tests with you before they are performed.

If your child has to have the affected kidney removed, it will be done through a procedure called a nephrectomy. The surgeon will discuss the risks and benefits of the procedure with you before it is performed.

Surgery is not usually done soon after birth for a multicystic dysplastic kidney. Instead, doctors will watch the kidney because most multicystic kidneys will shrink in size. However, doctors may recommend a nephrectomy if:

• The kidney grows or begins causing other problems, such as interfering with breathing or eating
• The doctor is worried about the way the kidney looks 
• You’re not able to bring your child in for regular follow-up care

How the kidney is removed will depend on your doctor, the size of the kidney and whether the ureter also will need to be removed. Your baby will need general anesthesia for the surgery. In most cases, babies who have a nephrectomy usually stay in the hospital only one night, and they recover quickly. 

Yes. Please ask your baby or child's nurse about ways to interact with and care for him or her. 

A nephrectomy requires general anesthesia (being put to sleep) and a minimum of an overnight stay. The surgeon will discuss the type of surgery, possible problems and the expected length of stay with you before they perform the procedure.

A baby with unilateral MCDK with no other birth defects has a normal life expectancy. For a child with only one kidney that works, that kidney may be a little bigger than normal. He or she will need follow-up to care for life to make sure the kidney remains healthy. It’s also important that your child:

• Limit the amount of salt and protein in the diet to the recommended daily requirements for their age
• Refrain from contact sports to protect the one good kidney from injury
• Maintain an ideal body weight
• Get regular exercise – this is important for all people, but it’s especially important for people with one kidney
• Have blood pressure checked at least once a year

Learn more by visiting: www.UrologyHealth.org.