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formulate a strategy for diagnostic imaging and a comprehensive plan of management.

A VCUG is performed within a month of age (44 weeks post-conception) even if the postnatal US was normal because 25% of the infants with normal postnatal studies will have reflux, while more than 40% of those with persistent hydronephrosis will have reflux. If reflux is diagnosed the children are generally switched over to Bactrim after 3 months of age and are maintained on antibiotic suppression until the reflux has resolved. In the absence of reflux, a renal scan is then performed. The renal scan should be performed in a pediatric nuclear medicine facility that adheres to the “well-tempered renogram” protocol developed by the Society for Fetal Urology and the Pediatric Nuclear Medicine Club. Surgery for the correction of obstruction is indicated by: (1) Urologist interpretation of the renal scan (2) differential renal function less than 40%, (3) recurrent UTI, (4) increasing hydronephrosis, and (5) compensatory renal growth of the contralateral normal kidney. If ureteral obstruction is found, (whether it lies at the UPJ, UVJ or mid ureter), surgery is required. If non-obstructive dilatation is diagnosed, or if our imaging studies are equivocal, then the US should be repeated approximately every 3 months for the first year, and a renal scan is repeated if there is a change for the worse or the clinical situation changes. Multicystic dysplastic kidneys are followed by serial US studies. Dysplastic kidneys require removal

only if their size presents problems with pulmonary or gastrointestinal function, they increase in size rather than regress over time, or if they are associated with infection. Associations between multicystic and hypertension and malignancy remain anecdotal at this time. Duplex kidneys with or without ureteroceles are managed according to the clinical situation and the effect, if any, on all existing functioning moieties. If a neurogenic bladder or prune belly syndrome is discovered then bladder function must be assessed and efficient emptying must be assured.

#### Postnatal diagnostics & Management

Truly obstructive lesions produce renal ischemia and loss of function. Infection makes matters worse and increases the risk of permanent renal injury. Surgical correction of suspected obstruction is highly successful in infants and children of all ages. The natural history of non- operated hydronephrosis is poorly defined, however, and the validity of the diagnostic tests used for assessing these dilated upper urinary tracts remains unproven. Understandably, the management of these children is controversial. The postnatal US is best delayed 3rd until the day of life. Earlier studies have a good chance of being falsely normal owing to a low glomerular filtration rate and relative dehydration. If Hydronephrosis is confirmed, we recommend placing the infant on amoxicillin 10mg/kg/day. If antenatally there is suspicion for posterior urethral valves (PUV), significant (grade 3 or 4) bilateral Hydronephrosis or unilateral hydronephrosis in a solitary functioning kidney, then the postnatal US should be performed without delay and followed by the VCUG. In these cases, serum chemistries should also be checked closely, and any additional workup (DR in the case of hydronephrosis) or intervention (valve resection or vesicostomy in the case of PUV) should be expedited.

#### Summary

Surgery for the correction of urinary tract obstruction is safe, definitive, and should be performed when obstruction is defined. Unfortunately, there is no gold standard for the evaluation of neonates and young infants. Children with antenatally detected hydronephrosis should be thoughtfully, carefully and thoroughly evaluated. Close surveillance can be practiced and continued until the hydronephrosis has resolved spontaneously or until obstruction has been proven.

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