Uretro-Pelvic-Junction Obstruction

• Most common obstructive lesion, most common cause of hydronephrosis in  in childhood
• Most cases are detected in newborns during routine in utero renal ultrasonography.
• Believed to be related to abnormal embryologic development of the proximal (upper) ureter.
• Usually caused by intrinsic stenosis.
• Internal constriction (focal narrowing or adynamic segments)
• External compression: ureteral kinks or angulations or abnormal vessel crossing, i.e. an accessory artery to the lower pole of the kidney 
• Renal function may be impaired from pressure atrophy.
• There is a whole segment of UPJ abnormalities called anomalous UPJ.

Presentation

• UPJ obstruction most commonly presents:
  • may be asymptomatic
  • maternal US shows fetal hydronephrosis
  • palpable renal mass in newborn/infant
  • abdominal/flank/back pain
  • febrile UTI
  • hematuria after minimal trauma; occasionally, mild or moderate UPJ obstruction may be undetected until there is trauma to the kidney or an abnormal flow of urine into the obstructed area. Such insults can occur after copious intake of fluids or the use of diuretics
     

Epidemiology

• 60% on Left
• 10% bilateral
• more in males 2:1
   

Diagnosis

• Renal US will reveal hydronephrosis
• In a fetus where renal pelvis dilation seen on prenatal US and baby is asymptomatic, dx is difficult. Repeat US after DOL 3 (nbn oliguria may mask). If US negative, repeat US in one month.
• Because the significance/grade of  the obstruction (eg, complete or partial) is essential to determining ultimate management, diuretic renography (renal scan) should follow the ultrasonography. Using a tracer such as Mag 3, a renal scan will assess the uptake of blood by the kidney and excretion of urine. If there is a delay in excretion, a small dose of a diuretic (eg, furosemide) is administered. Subsequently, the extent of excretion of urine and time course necessary for complete emptying of the renal collecting system determines the extent of the obstruction.  
• VCUG (15% have reflux). 

Treatment

• The cause and extent of the obstruction is vital to the ultimate management.
• Most newborns who have UPJ obstruction have only mild hydronephrosis, and surgery is usually unnecessary.
• In more severe cases of obstruction, the patient is vulnerable to the development of urinary tract infection and subsequent renal scarring, and surgery may be required.
• Repair of UPJ obstruction remains a controversial topic.
• Mild UPJ obstruction usually does not require repair because the efficacy of surgery is not guaranteed and the risk for kidneys exhibiting minor obstruction is minimal.
• Moderate-to-severe obstruction, as indicated by delayed washout of the tracer on diuretic renography, usually requires surgical repair. T
• he surgery involves excision of the obstruction, reconnection of the renal pelvis and ureter, and reduction, if present, of the oversized renal pelvis. The complication rate is low (success 91-98%), but some patients will experience a recurrence of the obstruction. Hence, repeat ultrasonography and renography are required within the first 6 months  after surgical repair.

Differential dx:
• megacalyciosis: congenital, nonobstructive calyx dilation without pelvic or ureteral dilation
• vesiculureteral reflux
• midureter or distal obstruction when ureter not well visualized on urogram