Hydronephrosis is when there is “stretching” or dilation in the kidney where urine collects. It
may occur in one or both kidneys. This dilation may be caused by a blockage (obstruction),
vesicoureteral reflux (VUR) or for no obvious reason. This blockage occurs somewhere along
the urinary system. This causes the urine to become trapped and the kidney to dilate.
Vesicoureteral reflux is when the urine travels backwards into the kidney causing the dilation.
Many times, children who have hydronephrosis are born with it. Sometimes it is unknown why
babies develop hydronephrosis.
Hydronephrosis is graded on a four point system and is classified by the amount of dilation
within the kidney. The grade of hydronephrosis depends on the amount of dilation, number of
calyces (small collecting cups within the kidney) seen and the presence and severity of kidney
tissue thinning. This is seen by ultrasound imaging.
Grading of Hydronephrosis:
Grade 1: mild “stretching” or dilation of the renal pelvis (where urine collects and drains to the
Grade 2: moderate “stretching” or dilatation of renal pelvis including a few calyces
Grade 3: “stretching” or dilatation of the renal pelvis, seeing all the calyces, which are
uniformly “stretched” or dilated, and normal kidney tissue
Grade 4: “stretching” or dilatation of the renal pelvis, seeing all of the calyces, and thinning of
the kidney tissue
Hydronephrosis is diagnosed by ultrasound. It may also be found with other image testing
during an evaluation for other symptoms. Often children may have no symptoms. Some patients
with severe hydronephrosis and have a blockage may have kidney pain, vomiting and urinary
Hydronephrosis is carefully monitored with periodic ultrasound imaging of your child’s kidneys.
How often your child has ultrasounds will depend on several factors and will be determined by
your provider. Your provider may order further tests. This may include a voiding
cystourethrogram (VCUG) or kidney scans. If your child’s hydronephrosis is caused by a
blockage, your child may need surgery. This will be discussed with you by your provider.
Pediatric Urology Clinic: (608) 263-6420
After hours, the clinic number will be answered by the paging operator. Ask for the Pediatric
Urology Resident on call. Leave your name and phone number with the area code. The doctor
will call you back. If you live out of the area, call 1-800-323-8942.
Your health care team may have given you this information as part of your care. If so, please use it and call if you
have any questions. If this information was not given to you as part of your care, please check with your doctor. This
is not medical advice. This is not to be used for diagnosis or treatment of any medical condition. Because each
person’s health needs are different, you should talk with your doctor or others on your health care team when using
this information. If you have an emergency, please call 911. Copyright © 10/2015 University of Wisconsin Hospitals
and Clinics Authority. All rights reserved. Produced by the Department of Nursing. HF#7767