Hydronephrosis/Urinary Tract Dilation

What is hydronephrosis?

Hydronephrosis means that the area of the kidney where urine is collected is enlarged or dilated. It can range from mild to severe, depending on the extent of the dilation. Often children who have hydronephrosis are born with this condition.

Hydronephrosis Illustration Hydronephrosis refers to dilation of the pelvis and calyceals of the kidney where urine is collected. Here, the normal appearance of the renal pelvis is seen on the left, followed by cases of hydronephrosis ranging from mild to severe (left to right).

Antenatal (before birth) hydronephrosis has emerged as one of the most common fetal abnormalities. Due to the increased use of prenatal ultrasound, it is now seen in 1 out of 100 pregnancies. It can be detected as early as the first trimester of pregnancy and, in most cases, is followed throughout the remainder of the pregnancy with repeated ultrasounds.

Signs and symptoms

Many children with mild hydronephrosis may not have any symptoms and the condition may never be detected. In severe cases of hydronephrosis, those associated with the blockage of urine, children may experience acute kidney pain, bleeding or urinary tract infections.


  • Vesicoureteral reflux (VUR). VUR is a condition in which urine travels backward from the bladder towards the kidney and may affect one or both ureters (the tubes that carry urine from the kidney to the bladder).
  • Obstruction or blockage. An obstruction can occur at the ureteropelvic junction (UPJ), where the ureter is connected to the kidney; the ureterovesical junction (UVJ) where the ureter meets the bladder; or in the urethra in boys (posterior urethral valve, PUV). A ureter may be associated with a ureterocele, which is a balloon-like obstruction at the end of the ureter.
  • No significant abnormality. The dilation in many of these kidneys eventually resolves over time.

Testing and diagnosis

Renal bladder ultrasound (RBUS)

This procedure uses sound waves to outline the kidneys and bladder. It will enable us to see the degree of hydronephrosis.

Voiding cystourethrogram (VCUG)

In a voiding cystourethrogram (VCUG), a catheter (tube) is placed through your child’s urethra into the bladder. The tube will be used to slowly fill the bladder with a contrast solution. While the bladder is being filled, a special machine (fluoroscopy) is used to take pictures. The radiologist looks to see if any of the solution is going back up into the kidneys. This study confirms the diagnosis of VUR. Additional pictures are taken while your child is urinating. The radiologist will look at the urethra while urine is passing to be sure there is no blockage noted (PUV, or discoordination with the urethral sphincter).

MAG III renal scan

This study will be performed to determine how each kidney is functioning and the degree of blockage, if noted. An intravenous line (IV) is used to inject a special solution called an isotope into the veins. The isotope makes it possible to see the kidneys clearly. Pictures of the kidneys will be taken with a large X-ray machine that rotates around your child.


MRI is a radiation-free diagnostic procedure that uses a combination of a large magnet, radiofrequencies and a computer to produce detailed images of the body. Magnetic resonance urography (MRU) creates detailed pictures of the kidneys, ureters and bladder.


Our team in the Division of Urology will take a thorough history, review any imaging with you, and tailor a treatment plan based on your child’s individual needs.

Resources for clinicians

This clinical pathway can be used to guide the evaluation and management of patients presenting with ultrasound findings of perinatal urinary tract dilation (UTD). This pathway should be used by pediatricians, neonatologists, and urologists to guide risk based evaluation and treatment based on pre-natal and post-natal ultrasound findings.

Review the pathway: Evaluation and Management of Neonates Presenting with Findings of Perinatal Urinary Tract Dilation.

Reviewed by: Division of Urology

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