AUA Summit - What is a Megaureter?


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What is a Megaureter?

Most children are born with a normal urinary tract. But in some infants the tube that connects the kidney and bladder gets wider. This can cause infections and block urine flow. If not treated, this can cause serious kidney damage.

What Happens under Normal Conditions?

The urinary tract is like a plumbing system, with special ‘pipes' that allow water and salts to flow through them. The urinary tract is made up of 2 kidneys, 2 ureters, the bladder, and the urethra.

The urinary tract is like a plumbing system, with special ‘pipes' that allow urine to flow through them. The urinary tract is made up of two kidneys, two ureters, the bladder and the urethra.

The kidneys act as a filter system for the blood. They remove toxins and keep the useful sugar, salts and minerals. Urine, the waste product, is made in the kidneys and flows down two 10- to 12-inch-long tubes called ureters into the bladder. The ureters are about a quarter inch wide and have muscled walls which push the urine into the bladder. The bladder stretches or expands to store the urine until it is time to empty by peeing. It also closes the pathways into the ureters so urine can't flow back into the kidneys. The tube that carries the urine from the bladder out of the body is called the urethra.

What are Megaureters?

A megaureter, or large ureter, is when a ureter is wider than three-eighths of an inch. This can result from an abnormality of the ureter itself (primary) or from the bladder being blocked (secondary). The types of megaureters are described below.

Primary Obstructed Megaureter

This type is when there is a narrowing where the ureter enters the bladder. This block causes the ureter to swell and get wider further up. The resulting pressure can damage the kidney over time. Surgery may be needed to fix the problem and remove the blockage. It is of great value to follow up with your health care provider even if there are no symptoms.

Refluxing Megaureters

In this type, the ureters are wider because of urine flowing back up the ureters from the bladder, which is called "vesicoureteral reflux". Normally, once urine is in the bladder, it shouldn't go back up the ureters. A refluxing megaureter is a sign of vesicoureteral reflux. This is more common in newborn males. Sometimes the reflux and stretched ureters get better over the first year of life, but if the problem doesn't go away, surgery may be needed. Refluxing megaureters may be linked to a health issue where the bladder doesn't drain all the way. Instead, it sends urine back up the ureters, and the bladder swells. This condition is called "megacystis megaureter syndrome."

Non-Obstructive, Non-Refluxing Megaureters

These are wide ureters that aren't caused by blockages or urine backflow. Many of these get better with time. Your health care provider will check carefully to rule out a blockage or reflux.

Obstructed, Refluxing Megaureters

This type is caused by a ureter that is blocked and also suffers from reflux. This is dangerous, as the ureters get bigger and more blocked with time. People with this problem are more likely to get urinary tract infections.

Secondary Megaureters

These are megaureters that show up as a result of other health problems. Some of these health problems that cause megaureters are:

  • posterior urethral valves (a blockage in the male urethra)
  • prune belly syndrome
  • neurogenic bladder (lack of normal control of the bladder from spina bifida, spinal cord injury, etc.)


Health care providers used to find most megaureters when checking a child with a urinary tract infection. These patients often have fever, back pain and vomiting.

Today, because of the widespread use of checking with ultrasound before birth, most megaureters are found as hydronephrosis or a stretched ("dilated") urinary tract before a baby is born.

Because megaureters can cause severe infection or blockages that lead to kidney damage, this health issue can be serious. Urinary tract stretching may suggest a blockage, but that's not always the case. In some cases, a dilated ureter may not affect the kidney at all. Also, most patients with megaureters found before birth don't get symptoms. It is of great value to have it checked to make sure it won't affect the way the kidney works and cause problems later.


If your child gets a urinary tract infection or other symptoms that could be signs of a megaureter, check with your health care provider. A urologist will likely do tests to check how your child’s urinary tract is working. Tests used to diagnosis megaureters are:


Ultrasound, also known as sonography, uses sound waves bouncing off organs in the body to make a picture of what's inside. This painless imaging test is often done to check how the kidney, ureters and bladder look. Ultrasound is very good at finding widened ureters. In fact, while sonography rarely picks up normal ureters because of their narrowed size, it makes great images of dilated ones.

Voiding Cystourethrogram (VCUG)

A VCUG is an x-ray test done to look for vesicoureteral reflux, or backflow of urine. A small tube ("catheter") is slid through the urethra into the bladder. A special dye is dripped into the bladder through the tube while x-rays are taken. If there's reflux, the x-ray will show the dye flowing back into the ureters and possibly the kidneys.

Diuretic Renal Scans

Diuretic renal (kidney) scans are used to check for blockages. This test is done by injecting a small amount of radioactive fluid into a vein, which then goes to the kidneys. A computer determines how each kidney is working. The renal scan also tells if a blockage is present.

Magnetic Resonance of the Urinary Tract (MR-U)

MR-U uses magnetic fields to make pictures of what's inside the body. This test shows the urinary tract even better than ultrasound or diuretic renal scans. MR-U involves injecting dye and getting pictures of the urinary tract using magnetic fields. This test isn't often used for small children because it calls for sedation or general anesthesia.


Open Surgery

If tests show a blockage or impaired kidney function, your child may need surgery to fix it. The typical surgery for megaureters involves putting the ureters back into the bladder away from the blockage ("ureteral reimplantation") and sometimes trimming the widened ureter ("ureteral tapering"). If your child doesn't have a urinary tract infection or decrease in kidney function, the surgery can be delayed until they are 1-2 years old. Surgery in infants isn't easy and should be done by surgeons skilled at pediatric surgery. Many babies are kept on antibiotics until surgery to help protect them from infections.

During the procedure, the surgeon makes a cut in the lower belly. Based on the child's anatomy, the surgeon will get to the ureter either through the bladder (transvesical) or from outside the bladder (extravesical). The ureter is removed from the bladder. If the ureter is very wide, it may need to be trimmed (tapered). Any blockages will be removed. The ureter is then replaced in the bladder. Your child may have a catheter for a few days to help healing. Your child will often stay in the hospital for between two and four days.

Most megaureters with symptoms are best treated by this open type of surgery. For obstructed megaureters, the blockage is removed. For refluxing megaureters, the reflux (urine back-up) is fixed. And for very wide ureters, the ureters can be trimmed.

Other Options

In children over two years old, balloon dilation of the narrowed part may be possible. The surgeon looks into the bladder with a long, thin telescope with a light at the end (cystoscope). A small wire is passed through the bladder opening and up the ureter. A balloon is used to stretch the narrowed part of the ureter. A silicone tube is left in the ureter for four to six weeks. Studies show this can clear the blockage and help most cases of reflux.

Minimally invasive methods, like injecting substances to fix reflux, usually don't work well because of the abnormal connection to the bladder.

Laparoscopy is surgery done through thin tubes put into the body through a small cut. The surgeon uses a special camera to see inside the body and very small, long instruments. Laparoscopy for ureteral reimplantation requires special training and should be done by a surgeon who has experience with this.

After Treatment

Some of the tests that were done before surgery may need to be repeated many weeks after surgery. This is to see how well the surgery worked. The size of the ureter may not get better right away after surgery, so it will need to be checked over time. Some problems that can arise from the surgery are:

  • bleeding
  • another blockage of the ureter
  • vesicoureteral reflux (new or ongoing)

A blockage may occur soon after the operation or after a longer period of time. This problem is seen in only 5 out of 100 of cases, but it may require more surgery. Vesicoureteral reflux problems are seen after surgery in 5 out of 100 of cases as well. This may go away on its own. Most patients are followed for a number of years after surgery. Ultrasound is used to make sure the look of the kidney and ureter continues to improve. A renal scan is often done to make sure the kidney is working properly and that the blockage is fixed. A VCUG is often done a few months after surgery to check for reflux.

Frequently Asked Questions

Is this condition genetic?

At this time, scientists don't know if there are genetic links.

Is surgery always needed to fix a megaureter?

No. Most megaureters found before birth get better over time without needing surgery. Megaureters found in older patients with pain or infection are more likely to need surgery. Antibiotics are often given to prevent urinary tract infection.

Is minimally-invasive surgery an option?

It may be possible to place a stent or catheter through the blocked part of the megaureter as a short-term fix to help the kidney drain. Stretching of a blockage in the ureter with a balloon is also possible in some cases. Laparoscopic surgery to fix megaureters is newer and less established, but can be offered in some places.

Are there long-term problems if we don't do anything?

Possibly yes. They include:

Updated May 2024. 

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