Should a renal diethylene‑triamine‑penta‑acetate (DTPA) scan be performed for a patient with mild right renal pelvis dilatation, minimal calyceal fullness, and an abrupt narrowing at the pelvi‑ureteric junction suggesting partial pelvi‑ureteric junction obstruction?

Renal DTPA Scan for Suspected Partial PUJ Obstruction

Yes, a renal DTPA scan is indicated for this patient with mild right renal pelvis dilatation, minimal calyceal fullness, and abrupt narrowing at the pelviureteric junction suggesting partial PUJ obstruction. Diuretic renography is the appropriate next step to differentiate true functional obstruction from non-obstructive dilation before considering surgical intervention 1.

Rationale for DTPA Scan

The key clinical challenge is distinguishing true obstruction requiring intervention from benign non-obstructive dilation that can be managed conservatively. The imaging findings described—mild pelvic dilatation with abrupt caliber change at the PUJ—create diagnostic uncertainty that requires functional assessment 1.

Why Functional Assessment Is Critical

• Diuretic renography (using DTPA or MAG3) differentiates functional obstruction from non-obstructive hydronephrosis by evaluating both split renal function and urinary drainage patterns after diuretic administration 1, 2.

• Not all hydronephrosis indicates obstruction—conditions like vesicoureteral reflux, physiologic dilation, or post-obstructive changes can cause collecting system dilation without true functional impairment 2.

• DTPA provides quantitative data on renal washout curves and split renal function, which are essential for surgical decision-making in equivocal cases 1.

Timing Considerations

• For infants, DTPA scans should be delayed until at least 2 months of age due to lower glomerular filtration rates in newborns, which can produce false-positive results 1.

• In adults or older children, the scan can be performed once the clinical question arises, as there are no significant physiologic barriers to accurate interpretation 1.

Clinical Context Supporting This Recommendation

PUJ Obstruction Characteristics

• PUJ obstruction is the most common cause of obstructive uropathy in children and can present with varying degrees of pelvic dilation 2.

• Partial PUJ obstruction may demonstrate compensated drainage with only mild pelvic dilation but disproportionate calyceal fullness, as described in this case 3.

• The abrupt caliber change at the PUJ is a key anatomic finding that raises suspicion for intrinsic obstruction or crossing vessel compression 4, 5.

Conservative Management Evidence

• Historical data demonstrates that dilated non-obstructed renal pelves managed conservatively show excellent outcomes, with 25 of 28 patients remaining well without intervention over 1-5 years of follow-up 6.

• Before objective functional assessment became available, many patients underwent unnecessary pyeloplasty for non-obstructive dilation 6.

• The correct management of dilated non-obstructed renal pelvis is conservative, making functional confirmation of obstruction essential before considering surgery 6.

Common Pitfalls to Avoid

Imaging Interpretation Errors

• Do not assume obstruction based solely on anatomic dilation—transient physiologic dilation is common and resolves spontaneously in 64-75% of pediatric cases 2.

• Ensure the bladder was not distended during initial imaging, as bladder distension, VUR, pregnancy, or diuresis can all cause collecting system dilation without true obstruction 2.

• Re-evaluate after bladder decompression if initial imaging showed bladder distension to avoid misdiagnosing physiologic dilation as obstruction 2.

Clinical Decision-Making Errors

• Do not proceed directly to surgery without functional confirmation of obstruction—even subtle radiological findings can mimic PUJ stenosis when the actual pathology is non-obstructive 7.

• Consider that crossing vessels may be contributing to partial obstruction, which has implications for surgical approach if pyeloplasty becomes necessary 5.

Algorithm for Management

1. Obtain DTPA renal scan with furosemide diuresis to assess split renal function and drainage patterns 1.

2. If the scan demonstrates functional obstruction (poor washout, decreased split function):

   • Refer to urology for consideration of pyeloplasty 8, 4
   • Minimally invasive techniques (endoscopic, laparoscopic, or robotic) are the gold standard for surgical intervention 4

3. If the scan shows non-obstructive dilation (normal washout, preserved split function):

   • Manage conservatively with periodic surveillance imaging 6
   • Monitor for development of symptoms, infections, or functional deterioration 8

4. For equivocal results, consider repeat imaging in 1-6 months to assess for progression 1.

1, 2, 4, 6