What is the management approach for bilaterally seen extrarenal pelvises?

Management of Bilateral Extrarenal Pelvises

Bilateral extrarenal pelvises are a benign anatomical variant that requires no intervention when confirmed, but initial evaluation must exclude true obstructive hydronephrosis through functional imaging. 1, 2

Critical First Step: Distinguish Anatomical Variant from Pathology

The immediate priority is determining whether you are dealing with an extrarenal pelvis (a normal variant) versus true hydronephrosis requiring urgent intervention. Extrarenal pelvis appears as a large hypoechoic mass outside the renal sinus but crucially lacks dilated calyces, parenchymal thinning, hydroureter, or kidney enlargement—features that distinguish it from pathologic hydronephrosis. 3

Key Distinguishing Features on Ultrasound:

• Extrarenal pelvis: Dilated pelvis outside renal sinus WITHOUT calyceal dilation, normal parenchymal thickness, no hydroureter 3
• True hydronephrosis: Dilated pelvis WITH calyceal dilation, possible parenchymal thinning, may have hydroureter 4, 3

Recommended Diagnostic Algorithm

Step 1: Assess Clinical Context

• Check serum creatinine and estimated GFR—bilateral disease eliminates contralateral compensation, so normal creatinine does NOT exclude significant obstruction 1, 2
• Obtain urinalysis to evaluate for infection or crystalluria 2, 5
• Determine if patient is symptomatic (flank pain, fever, urinary symptoms) or asymptomatic 2

Step 2: Obtain Functional Imaging to Confirm Diagnosis

If there is ANY uncertainty about whether this represents true obstruction versus extrarenal pelvis, proceed with MAG3 renal scan—this is the gold standard for differentiating functional obstruction from non-obstructive dilation. 1, 2 The MAG3 scan with diuretic administration provides perfusion and excretion data that definitively determines whether true obstructive uropathy exists. 1

Alternative advanced imaging options include:

• CT urography (CTU) without and with IV contrast: Provides comprehensive morphological and functional evaluation to identify any underlying pathology 1, 2
• MR urography (MRU) with IV contrast: Preferred if renal impairment is present, as it avoids nephrotoxic contrast 2

Step 3: Management Based on Findings

If MAG3 scan confirms non-obstructive extrarenal pelvis:

• No intervention required 6
• Conservative management with clinical observation 6
• No routine follow-up imaging needed unless renal function deteriorates or symptoms develop 5

If functional obstruction is identified:

• Urgent intervention required given bilateral involvement 1
• Identify and treat underlying cause (bladder outlet obstruction, retroperitoneal fibrosis, pelvic mass, etc.) 1, 2
• Consider urology referral for definitive management 4

Special Considerations for Extrarenal Pelvis

Associated Findings to Monitor:

• Extrarenal pelvis in neonates shows increased rates of vesicoureteral reflux (15%) and urinary tract infections (20.2% vs 1.2% in general population) 7
• Associated minor congenital malformations occur in 15% of cases 7
• Most cases show improvement or resolution over 2-year follow-up (81.5% in pediatric series) 7

Critical Pitfalls to Avoid:

• Do not assume bilateral pelvic dilation is benign without functional confirmation—bilateral disease puts both kidneys at simultaneous risk without contralateral reserve 1
• Do not rely on normal creatinine to exclude obstruction—serum creatinine can remain normal until late stages in bilateral disease 1
• Do not perform unnecessary pyeloplasty—before objective functional testing, dilated non-obstructed renal pelvises were inappropriately subjected to surgery 6
• Do not delay evaluation based on "minimal" appearance—even minimal bilateral hydronephrosis can represent early obstructive uropathy that progresses to irreversible nephron loss 1

Long-Term Management of Confirmed Extrarenal Pelvis

Once extrarenal pelvis is confirmed as non-obstructive:

• Clinical follow-up only, no routine imaging 6
• Monitor for development of symptoms (flank pain, hematuria, recurrent UTIs) that would prompt re-evaluation 5
• Maintain awareness of slightly increased UTI risk, particularly in pediatric patients 7
• No restriction on activities or specific interventions required 6