What is the management approach for a patient with a dilated extra renal pelvis?

Management of Dilated Extrarenal Pelvis

A dilated extrarenal pelvis is typically a benign anatomical variant that requires conservative management with observation and follow-up imaging, not surgical intervention. 1, 2

Understanding the Condition

An extrarenal pelvis is an anatomical variant where the renal pelvis extends outside the renal sinus, appearing as a large hypoechoic mass that can be mistaken for hydronephrosis on ultrasound. 2 The critical distinguishing features are:

• Absence of dilated calyces 2
• No parenchymal thinning 2
• No hydroureter 2
• Normal kidney size 2

This variant is more common in male infants and may be associated with minor congenital malformations (15.2% of cases). 3

Initial Diagnostic Approach

Confirm the diagnosis with renal ultrasound focusing on specific features:

• Measure the anteroposterior diameter of the renal pelvis 4
• Assess for calyceal dilation (should be absent in true extrarenal pelvis) 2
• Evaluate for ureteral dilation using color Doppler 4
• Check for ureteral jets in the bladder to confirm urinary outflow 4
• Perform imaging after bladder voiding, as a distended bladder can cause false-positive findings 4

If uncertainty exists about obstruction versus anatomical variant:

• Consider diuresis renography to objectively exclude obstruction 1
• Renal resistive index >0.70 or difference >0.04 between kidneys suggests pathologic obstruction requiring further evaluation 4

Conservative Management Strategy

The correct management is conservative observation without prophylactic antibiotics or surgical intervention. 1, 5

Monitoring Protocol

• Follow-up ultrasound at 3-6 months to ensure stability 4
• No routine antibiotic prophylaxis - studies show no significant difference in UTI rates between isolated moderate renal pelvis dilation and controls (rate ratio 1.146, p=0.8) 5
• Clinical assessment for symptoms of obstruction or infection 3

Expected Natural History

The condition typically follows a benign course: 5, 3

• Resolution: 41.5% complete resolution by 2 years 3
• Improvement: 40% show decreased pelvic width 3
• Stable: 22.6% remain unchanged without clinical deterioration 3
• Progression requiring intervention: <2% develop true hydronephrosis 3

When to Escalate Care

Refer to urology if any of the following develop:

• Persistent or worsening dilation on serial imaging 4
• Development of symptoms: flank pain, recurrent UTIs, or signs of obstruction 4, 1
• Renal pelvis diameter >21 mm (right) or >25 mm (left) - high sensitivity/specificity for predicting need for intervention 4
• Evidence of impaired renal function on laboratory testing 4
• Associated findings: calyceal dilation, parenchymal thinning, or hydroureter developing on follow-up 2

Important Clinical Pitfalls

Avoid unnecessary surgical intervention: Before objective urodynamic testing became available, many patients with dilated non-obstructed renal pelvis underwent unnecessary pyeloplasty. 1 In a 5-year follow-up study, only 1 of 28 patients with confirmed non-obstructed dilated pelvis required surgery. 1

UTI management: While extrarenal pelvis patients may have slightly higher UTI rates (20.2% in neonates vs 1.2% in general population), this does not justify prophylactic antibiotics. 3 Treat UTIs when they occur, not prophylactically. 5

Distinguish from true obstruction: Urinary retention in the collecting system (found in 60% of cases on renal scanning) does not necessarily indicate obstruction requiring intervention. 3 Functional assessment with diuresis renography is essential when clinical concern exists. 1

Associated vesicoureteral reflux: Approximately 15% of extrarenal pelvis cases have concurrent VU reflux, though this is typically low-grade and not the primary cause of increased UTI risk. 3