Basics
Description
Ureteropelvic junction (UPJ) obstruction is a partial blockage of the kidney at the point where the renal pelvis transitions into the proximal ureter.
Epidemiology
- 45% of all cases of significant prenatal hydronephrosis are due to UPJ obstruction.
- Occurs more commonly in males (M/F 2:1)
- Left-sided lesion more common (66%)
- Bilateral in 10 " 40%
- 50% of patients have an additional genitourinary malformation, most commonly
- Vesicoureteral reflux
- Contralateral UPJ obstruction
- Multicystic dysplastic kidney
- Renal agenesis
- Of patients with VATER association, 21% have UPJ obstruction and thus should be screened with renal ultrasound. (VATER stands for vertebral defects, anal atresia, tracheoesophageal fistula with esophageal atresia, and radial and renal anomalies.)
Pathophysiology
- The obstruction can cause varying degrees of hydronephrosis.
- Mild forms of UPJ obstruction result in dilation of the renal pelvis without loss of function.
- More severe forms result in dilation of the renal pelvis and calyces with loss of renal parenchyma and decreased function.
- In the most severe cases, the kidney may have cystic dysplasia and very poor function.
- Congenital hydronephrosis owing to an intrinsic narrowing is nearly always asymptomatic.
- When the obstruction is intermittent owing to a crossing vessel, the renal pelvis becomes distended (most commonly owing to a transient increase in urine output), which drapes it over the vessel and kinks the ureter, resulting in an acute obstruction. The acute distention of the renal pelvis results in pain (renal colic).
Etiology
- Intrinsic: a congenital narrowing of the UPJ, which is most commonly owing to abnormal musculature and fibrosis of this area, resulting in an adynamic segment
- Extrinsic: kinking at the UPJ, which is most commonly owing to the renal pelvis draping over a lower pole crossing vessel. This type of obstruction can be intermittent.
Diagnosis
History
- Antenatal
- If unilateral, timing and severity of hydronephrosis and status of the contralateral kidney are factors.
- When bilateral or affecting a solitary kidney, renal insufficiency is a concern.
- The presence of oligohydramnios, increased renal echogenicity, and cystic changes are indicators of poor renal function and dysplasia.
- Postnatal
- Feeding intolerance/respiratory distress (very rarely caused by UPJ obstruction)
- Older children
- History of episodic abdominal (may not lateralize well), flank, or back pain
- Length of episodes (usually 30 minutes to several hours); associated nausea and vomiting
- Relation of episodes to fluid intake; history of urinary tract infections or gross hematuria
Physical Exam
- Newborn
- Palpate kidneys.
- Affected kidney may feel enlarged but should not be tense.
- A tense mass can indicate a severe obstruction and should be imaged promptly.
- Older child
- Careful abdominal exam for enlarged kidney and tenderness
- Costovertebral angle tenderness
Diagnostic Tests & Interpretation
Lab
- Newborn
- If bilateral or a solitary kidney, serial assessments of renal function are necessary (serum electrolytes and creatinine), starting at 24 " 48 hours of age.
- With a normal contralateral kidney, no immediate laboratory testing is necessary.
- Older children
- Urinalysis to detect hematuria or pyuria. Culture if infection is suspected
Imaging
Antenatally detected hydronephrosis: Infants with moderate to severe unilateral or bilateral antenatally detected hydronephrosis typically are evaluated with 3 imaging studies " renal/bladder ultrasound, voiding cystourethrogram (VCUG), and renal scan:
- Renal/bladder ultrasound: In most cases, immediate imaging is not necessary. Because of a period of relative oliguria of a newborn in the first 24 " 48 hours of life, an ultrasound may underestimate the degree of hydronephrosis. This should not preclude evaluating an infant during this time as long as any normal study is followed up with a repeat study in 4 " 6 weeks. Evaluation should reveal the severity of dilation of the renal pelvis and calyces, changes in the amount and echogenicity of the parenchyma, and the presence of cortical cysts:
- The evaluation of the full bladder is important for excluding dilated distal ureters, thickening of the bladder wall owing to outlet obstruction, and ureteroceles.
- In cases of bilateral hydronephrosis, a solitary hydronephrotic kidney, or a tense kidney on physical examination, imaging should be promptly performed.
- VCUG: This study will detect the presence of vesicoureteral reflux as well as exclude the presence of posterior urethral valves and other abnormalities of the bladder:
- The test can be delayed until after discharge from the nursery unless there is concern about posterior urethral valves, in which case it should be performed early.
- The presence of ureteral dilation on ultrasound strengthens the argument to perform a VCUG. The detection of vesicoureteral reflux, particularly in a circumcised male patient, may not confer benefit in their clinical management.
- Renal scan: This study can quantify the differential renal function or the amount each kidney contributes to overall renal function (the normal differential is 50% ± 5% for each kidney):
- The 2 most commonly used radionuclides are mercaptoacetyltriglycine (MAG-3) and diethylenetriamine penta-acetic acid (DTPA). In addition to the ability to detect diminished function, if there is poor drainage of the affected kidney, furosemide is given to wash out the radiotracer.
- The time for washing out half of the accumulated radiotracer (T1/2) is often given in the report.
- A prompt T1/2 (<10 minutes) is indicative of a nonobstructed kidney.
- A slower T1/2 may be indicative of obstruction when it is >20 minutes. An intermediate T1/2 (10 " 20 minutes) is indeterminate for obstruction. Owing to effects of hydration, the amount of hydronephrosis, and variables in the timing of the diuretic administration, the T1/2 may be unreliable.
- Intravenous pyelogram (IVP): This study is most useful for evaluating the anatomy of the kidney and the ureters:
- It can also be used for evaluating an older child with intermittent symptoms if it can be done during a symptomatic episode.
- A normal study during a symptomatic episode of abdominal or flank pain excludes an intermittent UPJ obstruction as the cause of the child 's pain.
- If a normal study is obtained while the child is asymptomatic, an intermittent UPJ obstruction remains a possible cause.
- Magnetic resonance urography (MRU): A new technique being studied that provides both anatomic and functional detail. Dynamic contrast-enhanced MRI requires sedation and placement of a bladder catheter. The images are obtained following infusion of gadolinium-DTPA. Furosemide is given 15 minutes before the start of the study. This technique is being studied for use instead of ultrasound and renal scans in the hope that it will be a more precise tool in deciding whether or not the child requires surgical repair.
Differential Diagnosis
- Vesicoureteral reflux: Higher grades of reflux will result in the dilation of the upper urinary tract.
- Distal ureteral obstruction: obstruction at the level of the bladder owing to ureterovesical junction obstruction, ureterocele, or an ectopic ureter
- Bladder outlet obstruction: dilation of the upper urinary tract secondary to obstruction of the lower urinary tract owing to posterior urethral valves, urethral atresia, or stricture
- Megacalycosis: congenital dilation and increased numbers of calyces without significant renal pelvis dilation or obstruction
- Multicystic dysplastic kidney: can be difficult to differentiate severe hydronephrosis from cysts by ultrasound. Renal scan will demonstrate no function in multicystic dysplastic kidneys.
- Triad syndrome: a triad of hypoplastic abdominal wall musculature, bilateral undescended testes, and dilation of the urinary tract (also known as prune belly syndrome or Eagle-Barrett syndrome)
Treatment
General Measures
- The decision to observe or surgically correct a UPJ obstruction depends on several factors. One must consider the age and overall health of the neonate, the amount of functional impairment of the kidney, whether it is a unilateral or bilateral process, the drainage pattern on renal scan, and whether or not it is symptomatic. There is no strict rule for who should be observed and who should undergo surgery. This decision should be made on an individual basis.
- Antibiotic prophylaxis
- Newborns should be started on a once-a-day daily dose of amoxicillin or cephalexin at 1/4 " 1/2 the normal therapeutic dose.
- The antibiotic can be switched to trimethoprim, trimethoprim/sulfamethoxazole, or nitrofurantoin at 2 months of age.
- The duration that infants should be left on antibiotics is controversial among practicing pediatric urologists. Almost all agree that infants should be started on prophylactic antibiotics at birth.
- They should be continued at least until the infant undergoes a VCUG to exclude reflux. Several factors including age, sex, and degree of hydronephrosis are taken into account when deciding whether or not to stop the prophylaxis.
- Observation
- Infants with the hydronephrosis thought to be owing to a narrowing at the UPJ are typically observed when there is preserved function (>40%) in the affected kidney, and the contralateral kidney is normal.
- The pattern of drainage is taken into account, and if there is prompt drainage and normal differential function (50% ± 5%), these patients are followed with less frequent follow-up studies than those with less function or poor drainage.
- Most patients have follow-up imaging studies done at 3 " 6-month intervals during their 1st year of life, and they are gradually spaced out as time goes by if the hydronephrosis remains stable or improves.
- Older children with hydronephrosis owing to a UPJ obstruction are often detected during a symptomatic episode. If the UPJ obstruction is asymptomatic and the function of the kidney is preserved, the child may be observed as well.
Surgery/Other Procedures
- The gold standard for the repair of the UPJ obstruction has been a pyeloplasty:
- During the procedure, the narrowed UPJ is most commonly excised, and the ureter is reanastomosed to the renal pelvis.
- This procedure is successful 95% of the time.
- Less invasive approaches include endoscopically incising the narrowing (endopyelotomy) or balloon dilation:
- These approaches have been used in adults with rates of success in the 50 " 70% range but are considerably less invasive.
- Endoscopic procedures have not been routinely offered as a 1st-line therapy for the treatment of UPJ obstructions because of their limited experience in children and the lower rates of success.
- Laparoscopic pyeloplasty is being performed in older children and adolescents and will likely be more common in the next several years. Robotically assisted procedures are now being done, further enhancing the minimally invasive approach. Both offer a similar rate of success to a traditional pyeloplasty with decreased perioperative morbidity because of the small incisions for the laparoscopic instruments.
Additional Reading
- Carr MC, Casale P. Anomalies in surgery of the ureter in children. In: Wein AJ, Kavoussi LR, Novick AC, et al, eds. Campbell-Walsh Urology. 10th ed. Philadelphia: W.B. Saunders; 2012.
- Darge K, Higgins M, Hwang TJ, et al. Magnetic resonance and computed tomography in pediatric urology: an imagining overview for current and future daily practice. Radiol Clin North Am. 2013;51(4):583 " 598. [View Abstract]
Codes
ICD09
- 753.21 Congenital obstruction of ureteropelvic junction
- 593.4 Other ureteric obstruction
- 593.70 Vesicoureteral reflux unspecified or without reflux nephropathy
ICD10
- Q62.39 Other obstructive defects of renal pelvis and ureter
- Q62.11 Congenital occlusion of ureteropelvic junction
- N13.8 Other obstructive and reflux uropathy
- Q62.7 Congenital vesico-uretero-renal reflux
SNOMED
- 95575002 obstruction of pelviureteric junction (disorder)
- 16619007 Congenital occlusion of ureter (disorder)
- 12897005 Congenital stricture of ureteropelvic junction (disorder)
- 373637000 Congenital vesicoureterorenal reflux (disorder)
FAQ
- Q: My unborn baby has hydronephrosis. My obstetrician told me that it is most likely a UPJ obstruction. Is my baby going to need surgery to correct this?
- A: Not necessarily; only ’ Ό1/3 of babies with significant hydronephrosis ultimately require surgical correction.
- Q: Will my child 's kidney look normal after the surgery to fix it?
- A: Often the kidney has less dilation and an improved appearance but not completely normal. Of greater importance is that there is no longer obstruction and the function is preserved or improved.