Diagnostic Ultrasound - Abdomen and Pelvis

Ureteropelvic Junction Obstruction
TERMINOLOGY
Abbreviations
• Ureteropelvic junction (UPJ) obstruction, pelviureteric
junction obstruction (PUJO)
Definitions
• Obstruction of urine flow at level of UPJ
IMAGING
General Features
• Best diagnostic clue
○ Marked hydronephrosis to level of UPJ without
dilatation of ureter
○ Renal pelvis disproportionately enlarged compared to
calyces
• Location
○ Left kidney 2x as commonly affected
○ 10-30% are bilateral
• Morphology
○ Likened to Hirschsprung disease of ureter with focal
transitional point and aperistaltic segment
Ultrasonographic Findings
• Grayscale ultrasound
○ Prenatal findings
– Pyelectasis or fetal hydronephrosis
– Anteroposterior diameter > 10 mm in 3rd trimester
fetus or newborn suggests obstruction
– Large urinoma or urine ascites in severe cases
– Oligo-, poly-, or euhydramnios
○ Postnatal findings
– Dilatation of renal pelvis and calyces to level of
ureteropelvic junction
– Marked ballooning of renal pelvis, out of proportion
to calyces
– Normal caliber ureter
– Normal bladder size and contour
– If longstanding, renal parenchymal atrophy with
hypertrophy of normal contralateral kidney
– Associated contralateral renal anomalies: Multicystic
dysplastic kidney, renal duplication, and agenesis
• Pulsed Doppler
○ Elevated resistive indices (RI) may correlate with degree
of obstruction when contralateral kidney normal
○ Strict cut off values do not pertain to pediatric
population due to changing RI values with age
• Color Doppler
○ Can be used to detect crossing vessel
○ Ureteral jets can be used to exclude complete
obstruction
• Endoureteral US
○ Demonstrate crossing vessels in more than 50% of UPJ
obstruction, most commonly anteromedial in location
○ Demonstrate septum between ureteral and renal pelvic
lumen in UPJ obstruction secondary to high insertion of
ureter
○ Useful to guide site of endopyelotomy to avoid damage
to adjacent vessels
Radiographic Findings
• IVP
○ Delayed nephrogram depending on degree of
obstruction
○ Contrast opacification of a markedly dilated renal pelvis,
with abrupt tapering into a normal caliber ureter
○ "Linear band" sign: Linear oblique crossing defect in
proximal end of ureter
• Retrograde ureteropyelography
○ Assess ureter if not visualized in other studies
CT Findings
• CECT
○ Marked dilatation of renal pelvis with nonvisualized or
normal caliber ureter
○ Delayed nephrogram and contrast excretion
○ ± acquired etiologies (e.g., crossing vessels, neoplasm,
retroperitoneal inflammatory conditions) and associated
abnormalities (e.g., renal malformation)
• CTA
○ Detect crossing vessels
MR Findings
• T2WI
○ Marked dilatation of T2 hyperintense renal pelvis with
nonvisualized or normal caliber ureter
• T1WI C+
○ Delayed nephrogram and contrast excretion
• MRA
○ Detect crossing vessels
Nuclear Medicine Findings
• Diuresis renography
○ Hydronephrosis with poor drainage, suggesting
obstruction
○ Assess differential renal function and degree of
obstruction, often preoperatively
○ "Homsy" sign: Delayed double-peak pattern; suggests
intermittent UPJ obstruction
Imaging Recommendations
• Best imaging tool
○ Ultrasound in both prenatal and postnatal evaluation
○ Nuclear renal scan to determine whether
hydronephrosis is obstructive and degree of obstruction
○ CT or MR to detect crossing vessel
• Protocol advice
○ Postnatal US should be done several days after birth due
to relative neonatal oliguria
○ CTA or MRA: Define vessels and their relation to UPJ
DIFFERENTIAL DIAGNOSIS
Multicystic Dysplastic Kidney
• Multiple cysts of varying sizes that do not communicate
• Largest cyst is not central as in UPJ obstruction
Hydronephrosis of Other Etiology
• Determine level of obstruction with associated findings
• Can also be secondary to vesicoureteral reflux
Extrarenal Pelvis
• Prominent renal pelvis beyond contour of kidney
Diagnoses: Urinary Tract
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