What is pelviectasis, a condition characterized by dilation of the renal pelvis, often associated with obstructive uropathies and urinary tract issues?

What is Pelviectasis?

Pelviectasis is dilation of the renal pelvis, a radiologic finding that represents mild expansion of the kidney's central collecting system and does not necessarily indicate obstruction or pathology. 1

Definition and Clinical Significance

Pelviectasis refers specifically to dilation of the renal pelvis, distinguished from more extensive urinary tract dilation (UTD) that may involve calyces, ureters, or bladder. 1 The term was historically used alongside "hydronephrosis," "caliectasis," and "pelvicaliectasis," though current consensus guidelines now favor the unified term "urinary tract dilation" (UTD) to describe all degrees of collecting system expansion. 1

Diagnostic Thresholds

The diagnosis of pelviectasis depends on the anteroposterior diameter (APD) of the renal pelvis measured on ultrasound:

• Antenatal (prenatal) thresholds: APD <4 mm before 28 weeks gestation and <7 mm after 28 weeks is considered normal. 1
• Postnatal thresholds: APD <10 mm represents physiologic dilation and does not require intervention. 1
• Mild pelviectasis: APD >5-7 mm 2, 3
• Moderate pelviectasis: APD >7-10 mm 2, 3
• Severe pelviectasis: APD >10 mm 2, 3

Distinguishing Pelviectasis from Obstruction

Doppler ultrasound can differentiate a dilated renal pelvis from prominent renal veins in the renal sinus, helping confirm whether true pelviectasis exists. 1 Importantly, pelviectasis does not automatically indicate obstruction—many non-obstructive conditions cause pelvic dilation. 1

Non-Obstructive Causes of Pelviectasis:

• Transient/physiologic dilation 1
• Vesicoureteral reflux (VUR) 1
• Distended bladder 1
• Pregnancy 1
• Post-obstructive dilation 1
• Diuresis 1

Obstructive Causes:

• Ureteropelvic junction (UPJ) obstruction 1
• Urolithiasis (kidney stones) 1
• Pelvic tumors 1
• Posterior urethral valves 1
• Ureterocele or ectopic ureter 1

Natural History and Prognosis

The vast majority of isolated pelviectasis resolves spontaneously without intervention:

• 90-100% of mild (P1) UTD resolves by 4 years of age 1
• In neonates with RPD <10 mm, renal collecting systems normalize spontaneously within 1 year of birth in all cases 2
• Among infants with isolated antenatal pelviectasis, 82% showed normal pelvic diameter or only mild pelviectasis at 23 months follow-up 4
• Only 5% of patients with isolated pelviectasis showed any deterioration during follow-up 4
• Renal growth remains normal in patients with isolated pelviectasis 4

Clinical Management Approach

For mild pelviectasis (APD <10 mm postnatally), conservative management with observation is appropriate, as these cases rarely require surgical intervention. 2, 4

When to Pursue Further Evaluation:

Additional imaging and urologic consultation are warranted when:

• APD ≥10 mm persists on postnatal ultrasound 2
• Bilateral pelviectasis suggesting possible obstructive uropathy 1
• Distal ureteral dilation ≥7 mm 1
• Associated risk factors: female gender, intact foreskin with P2/P3 UTD, known anatomic abnormalities 1
• Signs of infection or symptomatic presentation 1

Imaging Considerations:

• Ultrasound is highly sensitive (>90%) for detecting hydronephrosis/pelviectasis 1
• Postnatal ultrasound is more sensitive than prenatal ultrasound for detecting obstructive uropathies 2
• False-negative ultrasound results can occur with dehydration, early obstruction, or suboptimal image quality 1

Critical Pitfalls to Avoid

Do not assume pelviectasis equals obstruction—the dilated non-obstructed renal pelvis is a well-recognized entity that requires conservative management rather than surgical intervention. 5 Before objective urodynamic testing became available, many patients with non-obstructive pelviectasis underwent unnecessary pyeloplasty. 5

Re-evaluate patients after bladder decompression if the bladder was distended during initial imaging, as bladder distension can cause reversible collecting system dilation. 1

Consider that pelviectasis detected on screening does not predict urinary tract infection risk—in one study, none of the infants with pre- or postnatal pelviectasis developed symptomatic UTI, while 17 infants without pelviectasis did develop symptomatic infections. 2