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Age: 44

Sex: Male

Indication: Right flank pain

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Case #47


Findings

  • Mild right hydronephrosis with multiple echogenic foci in the right renal collecting system, some of which demonstrate ill-defined posterior acoustic shadowing
  • Anechoic structure in the lower pole of the right kidney measuring 2.1 cm, consistent with a simple cyst
  • Antidependent echogenic material in the urinary bladder with associated ring-down artifact
  • Normal appearance of the left kidney


Diagnosis

Emphysematous pyelitis

Sample Report

Findings concerning for right emphysematous pyelitis with mild right hydronephrosis. Gas is also present in the urinary bladder.

No perinephric collection identified.

Normal appearance of the left kidney.


Discussion

  • Emphysematous pyelitis is a rare infection resulting in gas in the renal collecting system that typically responds well to medical management
  • It should be distinguished from emphysematous pyelonephritis (gas in the renal parenchyma), which has a poorer prognosis and may require nephrectomy when severe
  • Look for echogenic material in the collecting system with associated “dirty” shadowing
  • Another artifact sometimes seen with gas along or within the wall of a fluid-filled structure (like the gallbladder or urinary bladder) is ring-down artifact
    • Unlike shadowing, ring-down artifact results in a relatively echogenic (rather than hypoechoic) band deep to a collection of gas and may be flanked by areas of shadowing
    • It is best appreciated in hypoechoic structures like the gallbladder and urinary bladder
    • It can be similar in appearance to comet tail artifact, which results from small calcific or crystalline structures rather than gas


Images

Multiple echogenic structures in the right renal collecting system (red arrows), concerning for gas. Echogenic structure near the anterior wall of the bladder (red arrow) with ring-down artifact (yellow arrows), which is a typical appearance for gas near or within the bladder wall. Followup noncontrast CT in this patient confirms right renal collecting system gas (red arrow) and gas in the urinary bladder (yellow arrow).

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