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Patient Story

An otherwise healthy 7-year-old boy presents with a one day history of crampy left-sided abdominal and flank pain associated with nausea and non-bilious vomiting. He is afebrile and denies recent trauma. He is voiding and stooling normally. Exam is unremarkable except for some tenderness to palpation over the left costovertebral angle. Urinalysis is negative for blood or infection. Serum creatinine is within normal limits. Radiographic imaging reveals moderate left-sided hydronephrosis without ureteral dilation and an absence of stones or masses (Figure 65-1). The contralateral kidney and bladder are normal. Renal function testing is consistent with obstruction in the left kidney. The boy undergoes surgical repair for ureteropelvic junction obstruction (UPJO). On follow-up, he has resolution of hydronephrosis and his symptoms.


Ultrasound image of the left kidney. The findings of hydronephrosis with no dilation of the ureter are suggestive of ureteropelvic junction obstruction (UPJO). (Used with permission from Lynn L. Woo, MD)


Prenatal detection of congenital abnormalities has significantly increased in the past two decades with advancements in ultrasound technology and improvements in prenatal care. Common genitourinary abnormalities, such as hydronephrosis and UPJO, are not only being identified more frequently in the perinatal period but are also being managed effectively in children at younger ages. Earlier treatment of such conditions is believed to improve the growth and development of the genitourinary system in these children as they mature into adulthood.


  • Pelviureteric junction obstruction.

  • Proximal ureteral narrowing or stricture.

  • Renal pelvic dilation.

  • Pelviectasis.


  • Of all congenital abnormalities detected during pregnancy, approximately 20 to 30 percent involve the genitourinary system, with the majority being hydronephrosis.14

    • Hydronephrosis is defined as abnormal dilation of the renal pelvis, with the anteroposterior diameter of the renal pelvis measured to be ≥5 mm in the perinatal period.57

    • Hydroureteronephrosis is defined as abnormal dilation of the renal pelvis and ipsilateral ureter.

  • UPJO is the most common cause of perinatal hydronephrosis, accounting for approximately 40 percent of cases.8

  • Large population studies have demonstrated a predominance of UPJO in males, with the male-to-female ratio being greater than 2:1, as well as a predilection for occurrence on the left side, particularly among neonates.912

  • Bilateral UPJO has been reported to range from 10 to 40 percent cases.10,11,13

Risk Factors

  • While there have been case reports of UPJO occurring in families,1416 there is currently no established genetic predisposition for congenital UPJO.

    • However, recent studies have postulated that abnormalities in various factors involved in nephrogenesis, including bone morphogenetic proteins (BMP’s), Wilm’s Tumor (WT1) gene, and human leukocyte antigen (HLA) genes, may contribute to ...

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