What is pelviectasis?

What is Pelviectasis?

Pelviectasis is a term describing dilation of the renal pelvis (the collecting system of the kidney), which is part of a spectrum of urinary tract dilation (UTD) that includes related terms such as pyelectasis, hydronephrosis, and pelvocaliectasis. 1

Definition and Terminology

• Pelviectasis specifically refers to dilation of the renal pelvis, measured by the anteroposterior diameter (APD) on ultrasound imaging 1
• The term is now being replaced by the more comprehensive "urinary tract dilation (UTD)" to standardize terminology across specialties and avoid confusion with related terms like hydronephrosis and pyelectasis 1
• UTD occurs in 1-2% of pregnancies and is most commonly a transient finding representing a normal variant 1

Diagnostic Thresholds

Prenatal (Antenatal) Criteria

• Before 28 weeks gestation: APD <4 mm is considered normal 1
• After 28 weeks gestation: APD <7 mm is considered normal 1
• Postnatal: APD <10 mm represents physiologic dilation 1

Classification Systems

The UTD grading system evaluates multiple parameters beyond just APD 1:

• Anterior-posterior renal pelvis diameter
• Central and peripheral calyceal dilation
• Renal parenchymal thickness and appearance
• Ureteral dilation
• Bladder abnormalities
• Amniotic fluid volume (prenatally)

Risk stratification divides cases into UTD A1 (low risk) versus UTD A2-3 (increased risk) prenatally, and P1 (low risk) versus P2-3 (intermediate/high risk) postnatally 1

Clinical Significance and Outcomes

Prognosis

• Approximately 80% of mild pelviectasis (APD 4-7 mm) in the second trimester resolves spontaneously 1
• In isolated antenatal pelviectasis, 82% show normal pelvic diameter or only mild pelviectasis by 2 years of age 2
• Deterioration occurs in only 5% of cases with isolated pelviectasis 2

Associated Conditions

Pelviectasis may indicate underlying pathology in a minority of cases 1:

• Vesicoureteral reflux (VUR) - the most common pathologic cause 1, 3
• Ureteropelvic junction (UPJ) obstruction 1, 4
• Ureterovesical junction obstruction 1
• Multicystic dysplastic kidneys 1
• Posterior urethral valves 1

Among children with neonatal pelviectasis, vesicoureteral reflux is found in approximately 24% of cases, with no correlation between the degree of dilation and presence or severity of reflux 3

Association with Aneuploidy

• Pelviectasis confers a positive likelihood ratio of only 1.5 for trisomy 21, representing minimal risk 1
• For isolated UTD without prior aneuploidy screening, counseling about noninvasive screening (cfDNA or quad screen) is recommended rather than diagnostic testing 1

Management Approach

Prenatal Management

For fetuses with isolated UTD A1 (low risk), a single ultrasound at ≥32 weeks gestation is recommended to determine need for postnatal follow-up 1

For fetuses with UTD A2-3 (increased risk), individualized follow-up ultrasound with planned postnatal follow-up is recommended 1

Postnatal Evaluation

• Postnatal ultrasound predicts renal abnormalities with 87% sensitivity and 95% negative predictive value 5
• When postnatal ultrasound is normal, additional investigations are rarely needed as significant abnormalities are uncommon 5
• Voiding cystourethrography (VCUG) should be performed in children with pelviectasis regardless of stage, side, or sex to evaluate for vesicoureteral reflux 3
• However, VCUG can be delayed when pelviectasis is isolated with APD 10-15 mm, as 70% will have normal studies 5

Surgical Intervention

• Surgery is required in approximately 10% of moderate to severe pelviectasis cases 4
• Among all cases of fetal pelviectasis, approximately 6% require surgery, primarily for progressive UPJ obstruction with APD >15 mm 5
• No infants with mild pelviectasis (APD ≤7 mm) typically require surgery 4

Important Clinical Pitfalls

• Normal prenatal ultrasound does not eliminate the need for postnatal evaluation if UTI occurs, as 7 of 9 children with abnormal post-UTI ultrasounds had normal prenatal studies 1
• Renal growth remains normal in isolated pelviectasis, so lack of growth should prompt investigation for other pathology 2
• Persistent mild pelviectasis may lead to postnatal morbidity including vesicoureteric reflux (7.9%), renal dysplasia (2.6%), and PUJ stenosis (2.6%), necessitating follow-up even for mild cases 4