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.

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.

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  Pelviureteric junction obstruction.

  
  
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  Proximal ureteral narrowing or stricture.

  
  
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  Renal pelvic dilation.

  
  
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  Pelviectasis.

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  Of all congenital abnormalities detected during pregnancy, approximately 20 to 30 percent involve the genitourinary system, with the majority being hydronephrosis.^1–4

  
  
  
  
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    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.^5–7

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

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

  
  
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  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.^9–12

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

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  While there have been case reports of UPJO occurring in families,^14–16 there is currently no established genetic predisposition for congenital UPJO.

  
  
  
  
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    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 familial cases of UPJO.^15,17–19

  
  
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  UPJO may often present in association with other congenital renal and non-renal abnormalities.²⁰

  
  
  
  
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    UPJO is found in ≥15 percent cases of horseshoe kidneys, and is reported to also occur with malrotated kidneys.^12,21–25

    
    
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    More than 1/3 of cases of hydronephrosis in ectopic kidneys, particularly pelvic kidneys, are due to UPJO.^25,26

    
    
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    Approximately 20 percent of children with VATER syndrome have UPJO.²⁷

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  UPJO may be primary (congenital) or secondary.

  
  
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  Primary UPJO (Figure 65-2).

  
  
  
  
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    Involves a congenital defect in which there is a narrowing of the ureteral lumen at the ureteropelvic junction that is associated with impairment of urinary transport and renal function.

    
    
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    True underlying etiology is still unknown but is believed to be likely multifactorial.^20,28

    
    
    
    
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      Intrinsic factors (Figure 65-3).

      
      
      
      
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        Incomplete recanalization of the ureter during embryologic development.^29,30

        
        
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        Abnormal ureteral muscle and fibrous tissue development that affects ureteral peristalsis.^31,32

      
      
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      Extrinsic factors (Figure 65-4).

      
      
      
      
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        Mechanical obstruction from lower-pole crossing vessel, which can be seen in up to 63 percent cases of UPJO.^33,34

  
  
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  Secondary UPJO.

  
  
  
  
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    Obstruction develops as a result of kinking at the UPJ from a severely dilated and tortuous ureter. The ureteral dilation is most often secondary to severe vesicoureteral reflux or congenital megaureter.

Clinical Features

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  As many cases of hydronephrosis and UPJO are detected by prenatal ultrasound imaging, or incidentally during imaging for pediatric trauma, many infants and children will be asymptomatic.

  
  
  
  
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    Hydronephrosis identified in the prenatal period may spontaneously resolve in the immediate postnatal period.³⁵

    
    
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    Hydronephrosis identified in the perinatal period may remain stable or spontaneously resolve as a child gets older, obviating the need for any intervention, especially in the absence of symptoms.^36,37

    
    
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    Hydronephrosis is not necessarily indicative of obstruction.

  
  
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  Symptoms/Presentation.

  
  
  
  
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    Flank/abdominal pain.

    
    
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    Nausea/vomiting (non-bilious).

    
    
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    Hematuria.

    
    
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    Urinary tract infection.

    
    
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    Failure to thrive.

  
  
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  Dietl’s crisis describes a combination of episodic upper abdominal pain or flank pain with nausea/vomiting, particularly during diuresis, which is associated with UPJO.

  
  
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  As children with UPJO may present with abdominal pain, nausea, and vomiting, they may often undergo prior evaluation for gastrointestinal or psychological etiologies before the genitourinary etiology is identified and a referral to a pediatric urologist is made.^38,39

  
  
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  Untreated UPJO may be associated with increased risk for failure of the affected renal unit, kidney atrophy, pain, recurrent infections, stone development, and/or hypertension in adulthood.

Laboratory Studies

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  Urinalysis may demonstrate gross or microscopic hematuria, thought to be due to rupture of mucosal vessels in the dilated renal pelvis.

  
  
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  Basic metabolic panel may reveal renal insufficiency, although in the setting of a normal contralateral kidney, this would be unlikely.

  
  
  
  
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    In evaluating newborns, one must bear in mind that postnatal serum creatinine will reflect maternal serum creatinine until at least 48 hours after birth.

Diagnostic Studies

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  Retrograde Pyelogram (Figure 65-5).

  
  
  
  
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    Anatomic study, typically performed at time of surgical repair.

    
    
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    Allows confirmation of anatomical abnormality and helps exclude the possibility that the hydronephrosis is actually from a more distal obstructive lesion.

    
    
    
    
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      Findings—Dilated renal pelvis with characteristic narrowing or kinking at the UPJ and a distal ureter of normal caliber.

  
  
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  Ultrasound Imaging (US) (Figure 65-1).

  
  
  
  
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    Anatomic study.

    
    
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    Findings suggestive of UPJO:

    
    
    
    
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      Hydronephrosis or dilated renal pelvis; AP diameter ≥5 mm in children.

      
      
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      Non-visualization of the ureter is the rule (as a normal ureter is not dilated, it is usually not visible on US).

      
      
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      Thinned parenchyma.

      
      
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      Abnormal renal growth.

  
  
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  Computed Tomography (CT) or Magnetic Resonance Imaging (with or without contrast) (Figure 65-6).

  
  
  
  
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    Anatomic and functional studies, more often used in older children.

    
    
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    CT involves considerable radiation exposure and should therefore be minimized in children.

    
    
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    Findings suggestive of obstruction:

    
    
    
    
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      Dilated renal pelvis +/– dilated calyces.

      
      
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      Narrowing of ureter at UPJ.

      
      
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      Crossing vessel.

      
      
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      Delayed uptake or excretion of contrast agent from the affected kidney.

  
  
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  Diuretic Renography/Renal Flow Scan (Figure 65-7).

  
  
  
  
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    Functional nuclear medicine study.

    
    
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    Measures differential renal function as well as renal excretion and drainage.

    
    
    
    
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      Most commonly used radiotracer agent is technetium-99m. mercaptoacetyltriglycine (MAG-3).

      
      
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      Furosemide is administered during the study to promote diuresis of agent.

    
    
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    Findings suggestive of obstruction:

    
    
    
    
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      Differential renal function of <40 percent in affected kidney.

      
      
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      Impaired or lack of uptake and/or clearance of radiotracer agent.

  
  
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  Time to clearance of 50 percent tracer agent (T_1/2).

  
  
  
  
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    Normal: <10 minutes.

    
    
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    Indeterminate: 10 to 20 minutes.

    
    
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    Obstructed: >20 minutes.