Understanding Hydronephrosis

Hydronephrosis Overview

Hydronephrosis is dilation of the kidney, specifically the renal pelvis (place where urine is stored after its production). This can be the result of an anatomic abnormality in the urinary tract or can be a variant of normal. Hydronephrosis secondary to obstruction is typically at the level of the kidney (uretero-pelvic junction obstruction, or UPJ) or the bladder (ureterovesical junction obstruction or megaureter). 
How is Hydronephrosis diagnosed?

Hydronephrosis is usually diagnosed in one of two ways.
  1. A prenatal ultrasound (ultrasound during pregnancy) may reveal a fetus with dilated kidneys. This occurs in 1 per 100 pregnancies.
  2. An ultrasound done as a routine evaluation for another medical problem, such as a urinary tract infection or incontinence, may also reveal hydronephrosis.
Once hydronephrosis is noted, whether is it during pregnancy or later, additional tests are often required in order to find out the significance of the hydronephrosis. These tests are important because children with hydronephrosis may have an anatomic abnormality or urinary tract blockage. Early diagnosis and treatment of a potential urologic abnormality can prevent urinary tract infections and permanent kidney damage or scarring.

What, if any, other test should be done?
  • VCUG (voiding cystourethrogram): This study gives us important information regarding the shape and size of the bladder, the bladder neck (or opening) and the tubes that drain the urine from the kidneys into the bladder, called ureters. It allows us to diagnose reflux (the abnormal back-flow of urine from the bladder into the ureter and up to the kidney). It also gives us additional anatomic information about the urethra (urine tube which takes urine from the bladder outside the body) to make sure no blockage is present (posterior urethral valves).
  • Kidney (Renal) Scan: This test may be done depending on the history of urinary tract infection(s), result of VCUG, and/or the severity of the hydronephrosis. It is used to better demonstrate the actual function and/or drainage of the kidneys. A kidney scan can also show if there is kidney damage and/or scarring that may have resulted from a previous urinary tract infection or long-standing hydronephrosis. Two types of renal scans are typically performed depending on the diagnosis.
  1. Lasix Renogram or MAG-III diuretic renogram to test for significant blockage in the urinary tract,
  2. DMSA renal scan to test for scarring or damage to the renal tissue (more common in patients with vesicoureteral reflux).
When should these tests be performed if a prenatal ultrasound showed hydronephrosis?
If your newborn baby had hydronephrosis (kidney, ureter, or bladder dilation) noted on a screening prenatal ultrasound, a repeat ultrasound should be conducted in the first few weeks of life. It is normal for a newborn to make less urine in the first day of life. If the ultrasound is done too early, it may falsely appear that the hydronephrosis is gone. Certain conditions seen on the ultrasound may warrant a more expeditious work-up and we will let you know if this is necessary (for example, in the event of severe hydronephrosis in both kidneys or a dilated bladder).

How is hydronephrosis graded and why is this important?
Hydronephrosis is graded on a scale from zero to four, with one being the mildest form and four being severe. Please see Figure 2. The degree of hydronephrosis is used to assist in decision making with regard to treating the underlying cause of the hydronephrosis and the ultimate prognosis of patients. More severe grades of hydronephrosis are associated with closer pediatric urology follow-up. For example, grade III and IV hydronephrosis (not due to vesicoureteral reflux) typically require a renal scan.


Why does hydronephrosis occur?

There are numerous reasons why hydronephrosis occurs. Potential diagnoses:
  1. Vesicoureteral reflux
  2. Non-obstructive hydronephrosis
  3. Ureteropelvic junction (UPJ) obstruction
  4. Ureterocele
  5. Posterior urethral valves
  6. Ureterovesical junction (UVJ) obstruction
  7. Megaureter
  8. Multicystic Dysplastic Kidney
  9. Ectopic ureter
  10. Neurogenic/nonneurogenic bladder
This list is quite extensive, but most often the cause of the hydronephrosis is from one of the first three (in bold) diagnoses. The special x-ray tests mentioned previously will help us to find the cause of the hydronephrosis.

Will my child require any medication to assist in treating the hydronephrosis?
If your newborn needs antibiotics, he or she will be given a low dose once a day. The pediatrician taking care of your baby in the delivery hospital will prescribe these antibiotics. The types of antibiotics prescribed are specific to the urinary tract with few, if any, side effects. The type and amount of antibiotics will change as your child gets older and gains weight. The goal of giving your baby antibiotics is to prevent kidney infections that may occur as a result of hydronephrosis. Once the special x-ray tests have been completed, we will be able to estimate the total time of antibiotic treatment.

Will the hydronephrosis go away or will my child require surgery?
Typically, non-obstructive hydronephrosis (ie., hydronephrosis secondary to dilation at the ureterovesical junction, the place where the ureter meets the bladder) and grade 1 to 3 hydronephrosis secondary to uretero-pelvic junction type hydronephrosis do not need surgical intervention and resolve over time. The timing of resolution depends on the severity of the hydronephrosis and is different for each child. Children diagnosed with dilation from uretervesical junction abnormalities called megaureters rarely if ever need surgical repair. Children with grade IV hydronephrosis (severe) are the most likely to require surgery to prevent renal damage and recurrent infection.
In This Section
Understanding Hydronephrosis