What is hydronephrosis?

The urinary system is made up of two kidneys, two ureters, the bladder and a urethra. The kidneys are the bean-shaped structures located just below the rib cage that make urine and filter waste products from the blood. The ureters are thin tubes that carry the urine from the kidneys to the bladder where it is stored until leaving the body. The urethra is the tube that carries urine from the bladder out of the body. The ureter connects to the kidney at the ureteropelvic junction (UPJ) and connects to the bladder at the ureterovesical junction (UVJ).

Hydronephrosis is the swelling or dilation of the kidney due to a buildup of urine. Hydronephrosis can occur on one side (called “unilateral”) or both sides (“bilateral”).

Causes

Obstruction: A blockage can occur where the ureter is connected to the kidney (UPJ) or where the ureter is connected to the bladder (UVJ). Boys can have a blockage in the urethra from posterior urethra valves (PUV), which are tiny leaflets of tissue that prevent the normal release of urine. A balloon-like structure at the end of the ureter (called a ureterocele) also causes blockage and is commonly associated with other urinary abnormalities. Significant obstructions may require surgery.

Vesicoureteral Reflux (VUR): VUR is a condition in which urine in the bladder flows backward or refluxes into the ureters and the kidneys. This reflux may occur in only one ureter or both and is graded from 1 (mild) to 5 (severe). Depending on severity, most children will outgrow VUR, but they will require regular follow-up and daily antibiotics to prevent kidney damage until the condition is resolved. Surgical correction may be needed if VUR is severe or if it does not resolve on its own as a child grows.

Symptoms

Children may experience back pain, blood in the urine or urinary tract infections if the hydronephrosis is severe. However, most children with hydronephrosis do not have any symptoms or discomfort.

Testing, diagnosis and treatment

In most cases, hydronephrosis will be discovered by an ultrasound of the fetus performed during pregnancy and will not change your prenatal care, but it may require more frequent monitoring throughout pregnancy and after delivery.

After delivery: If hydronephrosis is discovered on a prenatal ultrasound, a kidney ultrasound will be performed a few days after birth. If hydronephrosis persists, further diagnostic tests may be considered to evaluate for VUR or an obstruction. A low-dose daily antibiotic may also be prescribed to prevent infection.

Often hydronephrosis resolves on its own and no treatment is needed. If hydronephrosis persists and causes pain, urinary tract infections or affects kidney function, surgery may be required. A treatment plan will be determined with your child’s urology team based on your child’s individual needs.