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    The Pediatric Page

    2007 Update: “My Baby Has a Swollen Kidney” - May 2007

    Hydronephrosis, or dilatation of the urinary tract collecting system, is one of the most common findings on prenatal ultrasound and occurs in about 1% of pregnancies. As common as the diagnosis is, the predictive value of the prenatal finding for postnatal renal problems is poorly established, especially for the mild to moderate cases of dilatation.

    Two recent meta-analyses of the outcome of isolated antenatal hydronephrosis were recently published(1,2); both found variability in the definition of significant prenatal hydronephrosis as well as the predictive value for subsequent renal pathology. Although many of the infants with prenatally diagnosed hydronephrosis have transient, physiologic dilatation, it may also be secondary to more significant renal and urinary tract anomalies including ureteropelvic junction obstruction, uretero-vesicle junction obstruction, posterior urethral valve, prune belly syndrome, multicystic dysplastic kidney and vesico-ureteral reflux. In the meta-analyses, the risk of significant postnatal pathology increased significantly with the degree of dilatation and the rate of postnatal stabilization was high for the lower grades of dilatation. However, even in the mild group, there was an increase in the rate of postnatal pathology compared to normal controls (11.9% for mild, 45% for moderate and 88.3% for severe). The dilemma for the pediatrician is knowing who needs follow-up studies and what studies are indicated in order to identify infants with significant anomalies of the kidney and urinary tract system, but avoid unnecessary testing in infants with insignificant hydronephrosis(3).

    Using measurements made in 3rd trimester ultrasounds, a normal anterior posterior renal pelvic diameter (APD) is <7 mm. Mild hydronephrosis is 9-12 mm, moderate 9-15 mm, and severe and ≥15. These values represent uncomplicated dilatation of the renal pelvis. None of the studies cited provided information on the value of prophylactic antibiotics. The recommendation is based on the concern for a higher incidence of urinary tract infections but not on carefully controlled clinical trials. Infants with severe bilateral hydronephrosis, bladder distension or severe unilateral hydronephrosis should be evaluated on the first postnatal day of life. If the postnatal ultrasound shows hydronephrosis, a VCUG should be performed. Findings of caliectasis, cortical thinning, ureterocele, dilated ureters and renal echogenicity and bladder abnormalities also represent more complex diagnoses and should be evaluated in the immediate postnatal period. The following recommendations are limited to the finding of uncomplicated dilation of the renal pelvis:

    Normal Dilatation: 3rd trimester Ultrasound (US) AP diameter (APD) less than 7 mm
    If prenatal ultrasound in the third trimester shows a fetal kidney pelvis that has an AP measurement of less than 7 mm and no other abnormal findings (caliectasis, cortical thinning, ureterocele, dilated ureters, echogenicity in the kidneys or bladder abnormalities [thickened, key hole sign, inadequate emptying]), no further workup is indicated as long as the is baby clinically well.

    Mild Dilatation: 3rd trimester Ultrasound AP diameter (APD) of 7-10 mm
    If the ultrasound in the third trimester shows a unilateral dilated kidney pelvis (also referred to as hydronephrosis, pelviectasis or pyelectasis) that is “mild” or has an APD of 7- 10 mm, but no other abnormal findings (see above underlined), this is most likely a variation of normal.

    1. Follow-up ultrasound should be done in the 1st three months after birth to confirm that the hydronephrosis is indeed mild.

    2. No Prophylactic antibiotics.

    3. If follow-up ultrasound shows an APD less than 7 mm and the baby is clinically well, no additional follow-up is needed.

    4. If follow-up ultrasound shows APD 7-10 mm repeat renal US at 1 year of age. If that US shows APD 7-10 mm repeat US at 2 years of age.

    5. If any follow-up ultrasound shows APD greater than 10 mm do a VCUG to rule-out reflux. Give 25 mg/kg oral amoxicillin one hour prior to the VCUG. Consult Pediatric Urology to treat reflux if the VCUG is positive or evaluate for possible lasix renogram.

    Cross section of kidney showing the following: Pelviectasis is dilatation in the renal pelvis. Caliectasis is dilatation that occurs in the renal calices (where urine collects from the pyramids before it goes to the pelvis which then connects to the ureter). If there is caliectasis there is usually pelviectasis as well.

    Moderate Dilatation: 3rd trimester APD greater than 10, but less than 15 mm
    If ultrasound shows a unilateral dilated kidney pelvis that is more than “mild” or if APD is greater than 10 mm, but less than 15 mm and no other abnormal findings (see above underlined):

    1. Follow up ultrasound should be done prior to 5 weeks after birth. The ultrasound does not need to be done prior to discharge from the hospital. Ultrasound is preferably done at least 48 hours after birth to allow for the kidneys to adjust to extrauterine life. During the first 24-48 hours any dilatation may be underestimated due to the relatively “dehydrated” state of the kidney.

    2. No prophylactic antibiotics are needed.

    3. If the follow-up ultrasound shows an APD of less than 10mm follow guidelines above.

    4. If the follow-up ultrasound shows an APD that is between 10-15 mm perform a VCUG. If the VCUG is positive consult with Pediatric Urology; if negative do a follow-up ultrasound at 1 year.

    5. If the follow-up ultrasound shows increased APD of 15 mm or greater, start prophylactic amoxicillin and do a VCUG to rule out reflux. If reflux is present consult with Pediatric Urology. If VCUG is normal, refer to Pediatric Urology for assessment of the need for a lasix renogram.

    Severe Dilatation: 3rd trimester APD greater than or equal to 15 mm

    1. Start prophylactic antibiotics (once daily dose of 25 mg/kg amoxicillin orally).

    2. Patients should be referred to Pediatric Urology soon after birth to determine evaluation needs.

    Other Findings Are Present
    If prenatal ultrasound shows any abnormality in the urinary system such as bilateral kidney pelvic APD greater than 10 mm, caliectasis, cortical thinning, ureterocele, dilated ureters, echogenicity in the kidneys, or an enlarged bladder:

    1. Start prophylactic antibiotics (once daily dose of 25 mg/kg amoxicillin orally).

    2. Obtain a renal ultrasound prior to discharge from the hospital.

    3. Discuss the patient with Urology to determine timing and type of follow-up appointments and testing needed.

    Special thanks to Dr. Larry Baskin, Professor of Pediatric Urology, UCSF, for his review of these recommendations.

    References

    1. Sidhu, G, Beyene, J, Rosenblum, N. Outcome of isolated antenatal hydronephrosis: a systematic review and meta-analysis. Pediatr Nephrol 21:218, 2006.

    2. Lee, R.S, Cendron,M Kinnamon, D, Nguyen, Hiep. Antenatal hydronephrosis as a predictor of postnatal outcome: a meta-analysis. Pediatr. 118:586, 2007

    3. Baskin, Laurence Postnatal management of antenatal hydronephrosis, Up-to-Date, December, 2006.

    This information provided by David A. Lee, M.D., Division of Neonatology and Bernice Law, M.D., Division of Pediatric Radiology, California Pacific Medical Center Department of Pediatrics.