Diagnostic Ultrasound - Abdomen and Pelvis

Allograft Hydronephrosis
TERMINOLOGY
Definitions
• Dilated renal pelvis and calyces, usually secondary to
obstruction
○ ±hydroureter
IMAGING
General Features
• Best diagnostic clue
○ Dilated fluid-filled renal pelvis and calyces, persisting
when bladder is empty
• Location
○ Over 90% at ureterovesical anastomosis and distal 1/3 of
ureter
Ultrasonographic Findings
• Grayscale ultrasound
○ Fluid-filled dilatation of renal pelvis branching into
dilated calyces
○ Hydroureter may be present, producing avascular
tubular structure arising from renal hilum and extending
toward bladder
○ Note that distended bladder may cause functional
obstruction or reflux resulting in hydronephrosis
– Repeat scan with bladder empty
○ Low-level echoes within lumen suggest pus
(pyonephrosis) or blood (hemonephrosis)
– Clot may also be present in ureter and bladder
– Debris from infection may layer dependently
○ Highly echogenic shadowing intraluminal structures
represent stones
– However, small stones may be very difficult to detect
○ Highly echogenic, weakly shadowing masses suggest
fungal balls
○ Ultrasound is sensitive and specific for hydronephrosis
○ Ultrasound may be limited for site of obstruction and
cannot providefunctional information
• Color Doppler
○ Useful to distinguish hilar vessels from dilated renal
pelvis
○ Use Color Doppler to distinguish clot or debris from solid
tumor
– Useful to demonstrate tiny vessels within urothelial
tumors
○ Elevated resistive index (RI) > 0.7 may occur in
obstructive uropathy, but RI is nonspecific and rarely
diagnostic
○ "Twinkling" artifact allows confident diagnosis of
calculus
Nonvascular Interventions
• Antegrade nephrostogram is gold standard in
differentiating fixed from transient obstruction and for
localizing site of obstruction
• Invasive test requiring direct puncture of lateral calyx and
injection of iodinated contrast medium into collecting
system
• Usually combined with ultrasound guidance to access
collecting system
• Insertion of percutaneous nephrostomy catheter allows
decompression of urine until definitive therapy, which can
be performed through same access
• Antegrade pyelography not performed in acute infection
CT Findings
• Use of iodinated contrast limited by poor renal function
• More sensitive for fluid collections and calculi
• CT nephrostography useful for delineation of stricture
length and surrounding pathology
MR Findings
• T2WI
○ High signal in fluid-filled pelvis and calyces
○ Highly sensitive for fluid collection and allows
differentiation between hydronephrosis and renal cysts
○ Comprehensive high-resolution evaluation of entire
urinary tract, including distal to obstruction
– Localization of obstruction is superior to ultrasound
○ Fast sequences allow diagnostic study in poorly
cooperative patients
• MR urogram (MRU) can be performed without contrast
(T2WI) or with contrast (T1WI C+ FS)
○ Avoids potential side effects of iodinated contrast
medium administration but with risk for nephrogenic
systemic fibrosis in poor renal function
• Functional MR techniques not yet in wide clinical use
Nuclear Medicine Findings
• Tc-99m MAG3 renogram
• Can differentiate true obstruction from nonobstructive
dilatation
• Provides functional information
Imaging Recommendations
• Best imaging tool
○ Ultrasound is first-line imaging modality for allograft
dysfunction both in early postoperative period and later
○ Sensitive and specific for hydronephrosis but may be
limited for location and cause of obstruction
• Protocol advice
○ If bladder is distended, re-evaluate for hydronephrosis
when empty
○ Look for transition zone and cause for obstruction, such
as fluid collection, stone, or clot
○ Consider antegrade pyelography or MAG3 renogram to
differentiate obstruction from dilatation
○ MR or CT for level of obstruction (MR preferred [no
ionizing radiation] but CT in wide use)
DIFFERENTIAL DIAGNOSIS
Nonobstructive Dilatation
• May be seen early due to atony and denervation
• Associated with distended bladder
○ Resolves on bladder emptying
Pyo- or Hemonephrosis
• Dilated calyceal system filled with low-level echoes
• Clinical picture important for diagnosis
Ureteral Calculi
• Typical echogenic shadowing stone
Diagnoses: Kidney Transplant
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