Diagnostic Ultrasound - Abdomen and Pelvis

Hydronephrosis
TERMINOLOGY
Synonyms
• Renal collecting system dilation, pelvicalyceal dilatation,
pelvocaliectasis
Definitions
• Dilation of renal collecting (pelvicalyceal) system ±ureteral
dilation
IMAGING
General Features
• Best diagnostic clue
○ Dilated intercommunicating fluid-filled anechoic
channels (renal calyces and pelvis) on ultrasound
• Size
○ Severity of hydronephrosis depends on
– Degree of obstruction (partial or complete)
– Duration of obstruction
– Renal function and urine output
Radiographic Findings
• IVP
○ Radiologic technique more commonly replaced with CT
urogram (CTU/CT IVP)
– Many findings seen on traditional IVP also seen on CT
urogram
– Increasingly dense nephrogram in acute obstruction
– Site of obstruction seen as abrupt or gradual cut-off
±filling defect of contrast opacified column in urinary
tract
CT Findings
• NECT
○ Dilated hypodense renal collecting system
±hydroureter
○ High sensitivity in evaluating site and etiology of
obstruction (intrinsic [stone] or extrinsic)
○ Perinephric or periureteral fat stranding suggest reactive
inflammation
○ Ureteral rim sign: Thickening of ureteral wall secondary
to edema from stone impaction
• CECT
○ May show striated nephrogram &/or urothelial
enhancement in superimposed infection (pyelonephritis)
○ CTU/CT IVP useful in nonstone etiology (urothelial
neoplasm, necrosed/sloughed papillae, clot)
– Delayed contrast opacification of collecting system
– May see urine leak from forniceal rupture in highgrade
obstruction
– Useful in evaluation of parapelvic cysts, ureteropelvic
junction (UPJ) obstruction
– Diminished nephrogram with reduced parenchymal
thickness in chronic hydronephrosis
– Dilated renal collecting system ±ureter, widening of
forniceal angles, renal enlargement
MR Findings
• Utilized in pediatric population due to lack of ionizing
radiation to define site of obstruction, parenchymal loss
Ultrasonographic Findings
• Grayscale ultrasound
○ Anechoic intercommunicating fluid-filled spaces (calyces)
and pelvis ±hydroureter
– Presence of internal echoes within dilated collecting
system may represent underlying
infection/pyonephrosis
○ Renal enlargement based on degree of obstruction
– Mild hydronephrosis: Small separation of calyceal
pattern (splaying), normal bright sinus echoes, normal
parenchymal thickness
– Moderate hydronephrosis: Ballooning of major and
minor calyces, diminished sinus echoes, normal or
thinned parenchymal thickness
– Severe hydronephrosis: Massive dilatation of renal
pelvis and calyces, associated with cortical thinning
and loss of normal renal sinus echogenicity
○ Antenatal US: Renal pelvis AP diameter ≥ 4 mm prior to
20-week gestation
– Fetal renal pelvis diameter ≥ 7 mm at 20-28 weeks or ≥
10 mm beyond 28-week gestation requires postnatal
follow-up
○ Hydronephrosis secondary to UPJ obstruction
– Etiology for up to 48% of fetal hydronephrosis
– Dilated renal pelvicalyceal system with stenosed UPJ
○ Focal hydrocalyx/caliectasis: Congenital, infectious
stricture
– Anechoic cystic focus with smooth margin; may be
difficult to differentiate on ultrasound from renal cyst
• Pulsed Doppler
○ Resistive indices (RI) may be useful in differentiating
acute from chronic (atony, gravid uterus, vesicoureteral
reflux) obstruction
○ Obstructive hydronephrosis: RI > 0.7 or RI 0.08-0.1 higher
than normal contralateral side in unilateral obstruction
○ Arteriolar vasoconstriction in obstruction, hence reduces
diastolic arterial flow velocity
• Color Doppler
○ Presence of ureteral jets in bladder help exclude
complete ureteral obstruction on affected side
– Useful in pregnant patients
Nuclear Medicine Findings
• DMSA scan: Central photopenic area ±cortical scar
• MAG 3/DTPA scan: Central photopenic area at vascular
phase, tracer accumulation within hydronephrotic
collecting system with delayed drainage
Imaging Recommendations
• Best imaging tool
○ Early evaluation: Ultrasound
○ CT ±contrast (CTU): Helps to confirm and identify
etiology
• Protocol advice
○ Work-up of prenatal diagnosed hydronephrosis
– Post natal US for serial monitoring
– Voiding cystourethrogram to evaluate vesicoureteric
reflux or posterior urethral valves in severe cases
○ Postnatal US to be performed 4-7 days after birth
because of relative dehydration in 1st days of life: Falsenegative
sign of hydronephrosis
Diagnoses: Urinary Tract
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