AUA Summit - What is Horseshoe Kidney (Renal Fusion)?


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What is Horseshoe Kidney (Renal Fusion)?

Most people are born with two kidneys. But sometimes the kidneys form fused together. The information here will help you talk to your urologist if you or your child has this condition.

Horseshoe kidney occurs in about 1 in 500 children. It occurs during fetal development as the kidneys move into their normal position. With horseshoe kidney, as the kidneys of the fetus rise from the pelvic area, they become attached (“fused”) together at the lower end or base. By fusing, they form into a U shape, like a horseshoe. This is thought to happen more often in males than in females.

What Happens Under Normal Conditions?

The urinary tract is the body’s drainage system. It includes two kidneys, two ureters, a bladder and a urethra.

Healthy kidneys work day and night to clean our blood. These two bean-shaped organs are found near the middle of the back, just below the ribs. One kidney sits on each side of the spine.

Our kidneys are our body’s main filter. They clean about 150 quarts of blood daily. Every day, they form about one to two quarts of urine by pulling extra water and waste from the blood. Urine normally travels from the kidneys down to the bladder and out through the urethra.

As a filter, the kidney controls many things to keep us healthy:

  • Fluid balance
  • Electrolyte levels (e.g., sodium, potassium, calcium, magnesium, acid)
  • Waste removal in the form of urine
  • The regulation of blood pressure and red blood cell counts

When the kidneys are damaged or when a tumor grows, they may not function well. In most cases, some damage won’t cause too many problems. But, major damage may require more treatment, like dialysis.

As a child develops in the mother’s uterus, the kidneys form first in the child’s lower belly. They slowly move up to their final position on both sides of the spine as they develop.


Up to 7 out of 10 children and adults with this abnormality will have symptoms. These can include:

Horseshoe kidneys have symptoms much more often than do other types of abnormal kidneys.

Kidney cancer is rare in children, but cancer tumors are somewhat more likely to occur in horseshoe kidneys than in normal kidneys. Some symptoms of a kidney tumor are:



Treatment may not be needed if there are no symptoms. There isn’t a cure for horseshoe kidney, but the symptoms can be treated if they cause problems (“supportive treatment”).

Blockage of urine flow (“obstruction”) and urine flowing backwards from the bladder (“vesicoureteral reflux”) are very common in patients with horseshoe kidney. These can both be fixed with surgery.

Horseshoe kidneys can become blocked just as any normal kidney can. Surgery to remove blockages or kidney stones in the ureter is usually successful.

A horseshoe kidney is most often set lower and much closer to the front of the body than a normal kidney. It’s also more likely to be hurt when there’s trauma to the abdomen than is a normal kidney. Wearing a medical alert bracelet will let emergency care providers know to be aware of the chance of kidney damage. Children with a horseshoe kidney should avoid contact sports.

Updated April 2024. 

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