What is the evaluation and management of a left partially duplicated system with a non-functioning lower moiety due to primary Ureteropelvic Junction Obstruction (UPJO)?

Evaluation and Management of Left Partially Duplicated System with Non-Functioning Lower Moiety Secondary to Primary UPJO

For a non-functioning lower moiety (<10% differential function) in a partially duplicated system with UPJO, proceed directly to lower pole hemi-nephrectomy rather than attempting reconstructive surgery, as preservation efforts are futile when function is already lost. 1, 2

Initial Diagnostic Evaluation

Imaging Protocol

• Obtain renal ultrasound to confirm hydronephrosis of the lower moiety, assess parenchymal thickness, and identify the "Y-shaped" ureteral confluence characteristic of incomplete duplication 3, 1

• Perform Tc-99m MAG3 diuretic renal scan (preferred over DTPA) to quantify differential function of the lower moiety and document drainage patterns with T1/2 washout curves 4

  • MAG3 is superior due to 40-50% extraction fraction versus DTPA's 20%, providing better visualization in obstructed systems 4
  • Delay until at least 2 months of age due to immature glomerular filtration in neonates 4

• Consider CT urography or MR urography to define complex anatomy, particularly the distance from the UPJO to the ureteral confluence, which determines surgical approach 4, 3, 1

  • MRU provides detailed morphologic information without radiation but may require sedation in young children 4, 3

Functional Assessment Criteria

• Document differential renal function of the lower moiety specifically 4
  • <40% differential function indicates severely compromised moiety 4
  • <10% function is generally considered non-salvageable 1, 2
• Assess drainage with T1/2 >20 minutes indicating obstruction 4

Management Algorithm Based on Lower Moiety Function

Non-Functioning Lower Moiety (<10% Function)

Proceed to lower pole hemi-nephrectomy as the definitive treatment 1, 2, 5

• Reconstructive attempts are not justified when parenchyma is already non-functional 5
• This prevents future complications including recurrent infections, pain, and stone formation 6
• Preserves the functioning upper moiety without risk of iatrogenic injury from complex reconstruction 1, 2

Functioning Lower Moiety (>40% Function)

Surgical approach depends on anatomic distance from UPJO to ureteral confluence: 1, 2

Short Distance (≤3 cm from UPJO to confluence)

• Perform end-to-side pyeloureterostomy of the lower pelvis to the ureteral confluence 1, 2
• This utilizes the non-obstructed upper pole ureter as drainage conduit 2
• Can be performed open or laparoscopically 1

Long Distance (>3 cm from UPJO to confluence)

• Perform dismembered pyeloplasty of the lower moiety 1, 2
• Standard Anderson-Hynes technique adapted for duplex anatomy 1
• Laparoscopic or robotic approach is feasible with appropriate expertise 1, 6

Borderline Function (10-40% Function)

Individualized decision based on: 4

• Deteriorating function (>5% decline on consecutive scans) mandates intervention to prevent complete loss 4
• Stable marginal function with symptoms (pain, recurrent UTI) favors hemi-nephrectomy over complex reconstruction 1, 5
• Improving function in young infants may warrant observation with serial MAG3 scans every 3-6 months 7, 8

Perioperative Considerations

Antibiotic Prophylaxis

• Do NOT routinely prescribe continuous antibiotic prophylaxis for isolated UPJO in duplex systems, as data shows no benefit 7, 8
• Consider prophylaxis only if additional high-risk features present: female gender, distal ureteral dilation ≥7 mm, or concurrent vesicoureteral reflux 7, 8

Voiding Cystourethrography (VCUG)

• Obtain VCUG if moderate-to-severe hydronephrosis present to exclude vesicoureteral reflux, which occurs in 30% of duplex anomalies 4, 3
• Essential in males to rule out posterior urethral valves causing bilateral pathology 4, 8

Crossing Vessels Assessment

• Identify crossing vessels at the UPJO during preoperative imaging, present in approximately 50% of lower pole UPJO cases 1, 2
• Crossing vessels necessitate dismembered pyeloplasty with vessel transposition rather than pyeloureterostomy 1, 2

Critical Pitfalls to Avoid

• Do not attempt complex reconstruction on a non-functioning moiety (<10% function), as this exposes the patient to operative risk without functional benefit 1, 5
• Do not assume all hydronephrosis indicates obstruction—ensure MAG3 scan confirms poor drainage (T1/2 >20 min) before proceeding to surgery 4, 8
• Do not overlook the upper moiety—ensure it is not obstructed or refluxing, as bilateral pathology changes management 3, 5
• Avoid endoscopic approaches (endopyelotomy) in duplex systems with complex anatomy, as success rates are significantly lower (50% vs 73% in single systems) and risk injury to the upper moiety ureter 3, 9
• Ensure adequate hydration before MAG3 scan, as dehydration masks obstruction and yields false-negative results 3

Postoperative Surveillance

• Obtain ultrasound at 1-3 months post-surgery to document resolution of hydronephrosis 7, 3
• Repeat MAG3 scan at 3-6 months to confirm improved drainage (T1/2 <20 min) and stable/improved differential function 4
• Annual ultrasound surveillance for at least 2 years to detect late complications or contralateral pathology 3