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Rady Children's Specialists


What is hydronephrosis?

Hydronephrosis is a condition in which extra urine is seen within the kidney and sometimes the tube that drains the kidney, called the ureter. It is commonly found before birth (antenatally) and detected on prenatal ultrasound.

What are signs and symptoms of hydronephrosis?

Hydronephrosis is most commonly diagnosed on prenatal ultrasound, as early as the first trimester.
Older children may present with recurrent urinary tract infections or abdominal/flank pain with hydronephrosis.

How common is hydronephrosis?

Hydronephrosis is detected prenatally in 1 out of 100 babies.

What causes hydronephrosis and what tests are necessary?

Hydronephrosis can be mild, moderate, or severe and can affect one side or both sides. There are many potential causes including the following:

  • Blockage near the kidney, called a ureteropelvic junction (UPJ) obstruction
  • Blockage near the bladder, where the ureter drains the bladder, called the ureterovesical (UVJ) junction
  • Blockage in the urethra in a boy, called a posterior urethral valve
  • Kidney stone causing blockage in the kidney or ureter
  • Urine reflux, where the valve between the bladder and ureter allows urine to flow backwards, up to the kidney
  • No abnormality may be identified and the hydronephrosis resolves on its own

Once your child is found to have hydronephrosis, it is usually followed with renal bladder ultrasounds. Your child will also likely undergo a VCUG test. For this test a catheter is placed within the bladder and the bladder is filled with contrast dye as X-ray pictures are taken of the bladder. This test can help diagnose urine reflux and posterior urethral valves. Your child may also undergo a MAG-3 study. For this test an IV is placed to give a tracer that is taken up and excreted within the kidneys. A catheter is also placed to empty the bladder. The test can measure how quickly urine drains from the kidney and help diagnose a blockage in the kidney.

How is hydronephrosis treated?

This depends on the cause. Urine reflux may resolve spontaneously or may require surgical correction if it does not resolve. Urine blockage, such as UPJ obstruction, usually requires surgical repair with a procedure called a pyeloplasty to remove the blockage. Urethra blockage from posterior urethral valves will also require surgical correction. Some hydronephrosis does not require any intervention at all.