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Resolution Rate of Low Grade Hydronephrosis Diagnosed within the First Year of Life.
Ramiro J. Madden-Fuentes, MD, Erin McNamara, MD, Unwanaobong Nseyo, MD, Caroline Hollingsworth, MD, Ana Gaca, MD, John Wiener, MD, Jonathan Routh, MD, MPH, Sherry Ross, MD.
Duke University Medical Center, Durham, NC, USA.

Introduction:
With improving prenatal care and imaging availability, low grade hydronephrosis (SFU grades 1 and 2) is often diagnosed within the first year of life. There is uncertainty regarding the significance of low grade hydronephrosis as it pertains to resolution, need for antibiotic prophylaxis to prevent urinary tract infection (UTI), and role of surgery. Thus, in a cohort of infants <12 months of age, we hypothesized that isolated SFU grades 1 and 2 hydronephrosis frequently resolves, that UTIs are infrequent, and that progression to surgical intervention is minimal.
Methods:
After IRB approval, the ICD9 code (591) was used to identify patients <12 months of age with hydronephrosis between January 2004 and December 2009. Patients with vesicoureteral reflux (VUR), spina bifida (SB), ureterocele, or posterior urethal valves (PUV), age >12 months at diagnosis, no follow-up renal ultrasound after first post-natal diagnosis, and renal units with SFU grade 3 or 4 hydronephrosis were excluded. Only ultrasounds performed after the first week of life were reviewed. Resolution, stability, or worsening hydronephrosis, UTI (defined as bacterial growth on urine culture - >100,000 CFU/mL) or need for surgical intervention were noted.
Results:
A total of 1,496 infants with hydronephrosis were identified. 528 were excluded due to VUR (35.1%), 65 due to SB (4.3%), 31 due to ureterocele (2.1%), and 17 due to PUV (1.1%). Additionally, 193 (12.9%) patients were excluded due to hydronephrosis on post-natal imaging, 167 (11.2%) due to absence of follow-up renal ultrasound, 75 (5.0%) due to presence of only grades 3 or 4 hydronephrosis, and 3 (0.2%) due to corrective surgery performed elsewhere. The remaining 417 infants were analyzed. Mean age at diagnosis on first post-natal ultrasound was 1.2 months. There were 125 females (30%) and 292 males (70%). Prenatal diagnosis was present in 165 (39.6%) patients. In 417 patients, 624 renal units with SFU grades 1 (n=399) and 2 (n=225) met criteria. In renal units with grade 1 hydronephrosis, complete resolution occurred in 268 (67.2%) with a mean time to resolution of 9.3 months (median 4 mo, range 0-91). Hydronephrosis remained stable in 119 (29.8%) and worsened in 12 (3%). In renal units with grade 2 hydronephrosis, complete resolution occurred in 108 (48.0%) with a mean time to resolution of 8.4 months (median 4 mo, range 0-74). Hydronephrosis improved in 69 (30.7%), remained stable in 46 (20.4%) and worsened in 2 (0.9%), of which one required pyeloplasty. UTI occurred in 37 children (8.9%) of which 27 had ICU nosocomial infections. Pyelonephritis did not occur in the remaining 10 patients. Only 3 (<1%) patient had more than 1 UTI and these were all in ICU patients.
Conclusion:
Low grade hydronephrosis diagnosed within the first year of life remains stable or improves in 97.8% of patients. For isolated low grades of hydronephrosis in children <12 months of age, observation with a least 1 repeat ultrasound within the first year of diagnosis would be an appropriate method of surveillance. Given the low rate of recurrent UTI, antibiotic prophylaxis has a limited role in management.


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