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Ureteropelvic junction (UPJ) obstruction is a blockage of normal urine flow passing from the renal pelvis into the ureter. It occurs in approximately 1 in 500 live births. The vast majority of cases in infants and children are the result of an intrinsic narrowing at the UPJ, but older children and adolescents are frequently found to have an extrinsic compression of the junction secondary to a crossing renal vessel. Prolonged obstruction can have deleterious effects on the developing kidney.


The majority of UPJ obstructions are diagnosed prenatally, when the finding of hydronephrosis without ureteral dilation raises suspicion for the diagnosis. Postnatally, a confirmatory ultrasound is ideally performed after 48 hours of life to minimize the potential for false negatives due to relative dehydration at birth. Hydronephrosis can be classified based on the Society for Fetal Urology (SFU) grading system (Table 472-1). Representative ultrasounds are seen in Figure 472-1. A voiding cystourethrogram (VCUG) may be necessary to exclude vesicoureteral reflux (VUR) as the cause of hydronephrosis. Infants who are not diagnosed prenatally may be asymptomatic or present with a palpable abdominal mass, urinary tract infection (UTI), or failure to thrive. Children or adolescents may present with UTIs, hematuria, or a Dietl crisis, which is episodic abdominal pain accompanied by nausea and vomiting that occurs when the hydronephrosis is acutely worsened. The diagnosis of UPJ obstruction is often delayed in patients presenting with repeated Dietl crises, as it is often mistaken for gastrointestinal complaints.

Figure 472-1

Ultrasounds demonstrating hydronephrosis. Top left: Society for Fetal Urology (SFU) grade 1 hydronephrosis. Top right: SFU grade 2 hydronephrosis. Bottom left: SFU grade 3 hydronephrosis. Bottom right: SFU grade 4 hydronephrosis.


Most cases of prenatally diagnosed hydronephrosis are managed through close observation with serial imaging, as many infants may experience improvement or resolution in the first years of life. Starting at 2 months of age when the kidneys have reached an adequate maturation stage, diuretic renography can be used to assess the differential function of the affected kidney and degree of obstruction. Indications for surgical repair include recurrent pyelonephritis, abdominal or flank pain, and worsening of the differential function or ...

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