Diagnostic Ultrasound - Abdomen and Pelvis
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Diagnostic Ultrasound - Abdomen and Pelvis

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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 459

Hydronephrosis Diagnoses: Urinary Tract DIFFERENTIAL DIAGNOSIS Parapelvic Cyst • Lymphatic in origin or develop from embryologic rests • Well-defined anechoic renal sinus mass • No communication with pelvicalyceal system • CT urogram for confirmation Extrarenal Pelvis • No dilation of renal calyces or ureter • Focal ballooning of renal pelvis beyond contour of renal sinus Multicystic Dysplastic (MCD) Kidney • Developmental anomaly, a.k.a. renal dysplasia, renal dysgenesis, multicystic kidney usually unilateral • Small kidney with multiple noncommunicating cysts • Absence of both normal parenchyma and normal renal sinus complex Prominent Renal Vasculature • Mimics dilated renal pelvis on transverse scans • Vascular flow demonstrated on color Doppler Autosomal Dominant Polycystic Kidney • Bilateral enlarged kidneys with multiple asymmetrical cysts of varying size • Cysts with internal echoes if hemorrhage or infected Multilocular Cystic Nephroma • Uncommon benign cystic neoplasm • Seen as focal multilocular noncommunicating cysts PATHOLOGY General Features • Etiology ○ Obstruction: Stone, blood clot, sloughed papilla, crossing of iliac vessels, stricture (benign or malignant) – ± ureteric dilatation, depending on level of obstruction – Confirmation: CT urogram, antegrade/retrograde pyelography, isotope renogram – Chronic obstruction: Loss of renal parenchyma and function ○ Relieved obstruction – If obstruction is severe or prolonged, dilatation may not return to normal secondary to atony – Pulsed Doppler: Normal RIs ○ Reflux nephropathy – Usually focal caliectasis, associated with renal cortical scarring ○ Pregnancy – More marked on right side (from gravid uterus, sigmoid protective of left side) may become permanent after multiple pregnancies – Doppler: Normal ureteral jets in bladder; pulsed Doppler: Normal RIs ○ Congenital hydronephrosis: Isolated abnormality – Ureteropelvic obstruction, posterior urethral valve, ectopic ureterocele, prune belly syndrome, vesicoureteric junction obstruction ○ Papillary necrosis: Calyces with sloughed papillae become clubbed ○ Pyelonephritis: Calyceal clubbing, focal caliectasis, and cortical scar CLINICAL ISSUES Presentation • Most common signs/symptoms ○ Adults:Flank pain/hematuria for renal or ureteric stone ○ Pediatric: Abdominal mass ○ Neonate: Diagnosed on antenatal ultrasound Natural History & Prognosis • Urine leak from forniceal/renal pelvic tear if acute significant obstruction • Superimposed infection + obstruction, consider pyonephrosis, a surgical emergency • Parenchymal atrophy if chronic obstruction, leading to renal impairment DIAGNOSTIC CHECKLIST Consider • Communicating anechoic tubular spaces in kidney with altered renal sinus fat Image Interpretation Pearls • False-positive sign of hydronephrosis ○ Full bladder may cause distension of calyces, normal when bladder empty ○ Increased urine flow: Overhydration, medication, following urography SELECTED REFERENCES 1. Liu DB et al: Hydronephrosis: prenatal and postnatal evaluation and management. Clin Perinatol. 41(3):661-78, 2014 2. Jandaghi AB et al: Assessment of ureterovesical jet dynamics in obstructed ureter by urinary stone with color Doppler and duplex Doppler examinations. Urolithiasis. 41(2):159-63, 2013 3. Piazzese EM et al: The renal resistive index as a predictor of acute hydronephrosis in patients with renal colic. J Ultrasound. 15(4):239-46, 2012 4. Estrada CR Jr: Prenatal hydronephrosis: early evaluation. Curr Opin Urol. 18(4):401-3, 2008 5. Becker A et al: Obstructive uropathy. Early Hum Dev. 82(1):15-22, 2006 6. Sidhu G et al: Outcome of isolated antenatal hydronephrosis: a systematic review and meta-analysis. Pediatr Nephrol. 21(2):218-24, 2006 7. Moon DH et al: Value of supranormal function and renogram patterns on 99mTc-mercaptoacetyltriglycine scintigraphy in relation to the extent of hydronephrosis for predicting ureteropelvic junction obstruction in the newborn. J Nucl Med. 44(5):725-31, 2003 8. Perez-Brayfield MR et al: A prospective study comparing ultrasound, nuclear scintigraphy and dynamic contrast enhanced magnetic resonance imaging in the evaluation of hydronephrosis. J Urol. 170(4 Pt 1):1330-4, 2003 9. Grenier N et al: Dilatation of the collecting system during pregnancy: physiologic vs obstructive dilatation. Eur Radiol. 10(2):271-9, 2000 460

Hydronephrosis<br />

Diagnoses: Urinary Tract<br />

DIFFERENTIAL DIAGNOSIS<br />

Parapelvic Cyst<br />

• Lymphatic in origin or develop from embryologic rests<br />

• Well-defined anechoic renal sinus mass<br />

• No communication with pelvicalyceal system<br />

• CT urogram for confirmation<br />

Extrarenal <strong>Pelvis</strong><br />

• No dilation of renal calyces or ureter<br />

• Focal ballooning of renal pelvis beyond contour of renal<br />

sinus<br />

Multicystic Dysplastic (MCD) Kidney<br />

• Developmental anomaly, a.k.a. renal dysplasia, renal<br />

dysgenesis, multicystic kidney usually unilateral<br />

• Small kidney with multiple noncommunicating cysts<br />

• Absence of both normal parenchyma <strong>and</strong> normal renal<br />

sinus complex<br />

Prominent Renal Vasculature<br />

• Mimics dilated renal pelvis on transverse scans<br />

• Vascular flow demonstrated on color Doppler<br />

Autosomal Dominant Polycystic Kidney<br />

• Bilateral enlarged kidneys with multiple asymmetrical cysts<br />

of varying size<br />

• Cysts with internal echoes if hemorrhage or infected<br />

Multilocular Cystic Nephroma<br />

• Uncommon benign cystic neoplasm<br />

• Seen as focal multilocular noncommunicating cysts<br />

PATHOLOGY<br />

General Features<br />

• Etiology<br />

○ Obstruction: Stone, blood clot, sloughed papilla, crossing<br />

of iliac vessels, stricture (benign or malignant)<br />

– ± ureteric dilatation, depending on level of<br />

obstruction<br />

– Confirmation: CT urogram, antegrade/retrograde<br />

pyelography, isotope renogram<br />

– Chronic obstruction: Loss of renal parenchyma <strong>and</strong><br />

function<br />

○ Relieved obstruction<br />

– If obstruction is severe or prolonged, dilatation may<br />

not return to normal secondary to atony<br />

– Pulsed Doppler: Normal RIs<br />

○ Reflux nephropathy<br />

– Usually focal caliectasis, associated with renal cortical<br />

scarring<br />

○ Pregnancy<br />

– More marked on right side (from gravid uterus,<br />

sigmoid protective of left side) may become<br />

permanent after multiple pregnancies<br />

– Doppler: Normal ureteral jets in bladder; pulsed<br />

Doppler: Normal RIs<br />

○ Congenital hydronephrosis: Isolated abnormality<br />

– Ureteropelvic obstruction, posterior urethral valve,<br />

ectopic ureterocele, prune belly syndrome,<br />

vesicoureteric junction obstruction<br />

○ Papillary necrosis: Calyces with sloughed papillae<br />

become clubbed<br />

○ Pyelonephritis: Calyceal clubbing, focal caliectasis, <strong>and</strong><br />

cortical scar<br />

CLINICAL ISSUES<br />

Presentation<br />

• Most common signs/symptoms<br />

○ Adults:Flank pain/hematuria for renal or ureteric stone<br />

○ Pediatric: Abdominal mass<br />

○ Neonate: Diagnosed on antenatal ultrasound<br />

Natural History & Prognosis<br />

• Urine leak from forniceal/renal pelvic tear if acute<br />

significant obstruction<br />

• Superimposed infection + obstruction, consider<br />

pyonephrosis, a surgical emergency<br />

• Parenchymal atrophy if chronic obstruction, leading to<br />

renal impairment<br />

DIAGNOSTIC CHECKLIST<br />

Consider<br />

• Communicating anechoic tubular spaces in kidney with<br />

altered renal sinus fat<br />

Image Interpretation Pearls<br />

• False-positive sign of hydronephrosis<br />

○ Full bladder may cause distension of calyces, normal<br />

when bladder empty<br />

○ Increased urine flow: Overhydration, medication,<br />

following urography<br />

SELECTED REFERENCES<br />

1. Liu DB et al: Hydronephrosis: prenatal <strong>and</strong> postnatal evaluation <strong>and</strong><br />

management. Clin Perinatol. 41(3):661-78, 2014<br />

2. J<strong>and</strong>aghi AB et al: Assessment of ureterovesical jet dynamics in obstructed<br />

ureter by urinary stone with color Doppler <strong>and</strong> duplex Doppler<br />

examinations. Urolithiasis. 41(2):159-63, 2013<br />

3. Piazzese EM et al: The renal resistive index as a predictor of acute<br />

hydronephrosis in patients with renal colic. J <strong>Ultrasound</strong>. 15(4):239-46, 2012<br />

4. Estrada CR Jr: Prenatal hydronephrosis: early evaluation. Curr Opin Urol.<br />

18(4):401-3, 2008<br />

5. Becker A et al: Obstructive uropathy. Early Hum Dev. 82(1):15-22, 2006<br />

6. Sidhu G et al: Outcome of isolated antenatal hydronephrosis: a systematic<br />

review <strong>and</strong> meta-analysis. Pediatr Nephrol. 21(2):218-24, 2006<br />

7. Moon DH et al: Value of supranormal function <strong>and</strong> renogram patterns on<br />

99mTc-mercaptoacetyltriglycine scintigraphy in relation to the extent of<br />

hydronephrosis for predicting ureteropelvic junction obstruction in the<br />

newborn. J Nucl Med. 44(5):725-31, 2003<br />

8. Perez-Brayfield MR et al: A prospective study comparing ultrasound, nuclear<br />

scintigraphy <strong>and</strong> dynamic contrast enhanced magnetic resonance imaging in<br />

the evaluation of hydronephrosis. J Urol. 170(4 Pt 1):1330-4, 2003<br />

9. Grenier N et al: Dilatation of the collecting system during pregnancy:<br />

physiologic vs obstructive dilatation. Eur Radiol. 10(2):271-9, 2000<br />

460

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