KEY FACTS
Terminology
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Gas-forming upper UTI involving renal parenchyma &/or perinephric space
Imaging
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Highly echogenic areas within renal sinus and parenchyma with “dirty” shadowing
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Ring-down artifacts: Air bubbles trapped in fluid
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Perinephric fluid collections may be seen
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Type I (33%): Parenchymal replacement by gas, ± crescent of subcapsular or perinephric gas
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Type II (66%): Renal or perirenal fluid abscesses with bubbly gas pattern ± gas within renal pelvis
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Evaluation for psoas abscess and spinal osteomyelitis essential
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CT may help further delineate location and extent of renal and perirenal gas
Top Differential Diagnoses
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Emphysematous pyelitis
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Gas limited to renal collecting system and pelvis, not parenchyma
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Less clinically serious than emphysematous pyelonephritis, unless obstructed
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Pathology
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Single or mixed organism(s) infection
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Escherichia coli (68%), Klebsiella pneumoniae (9%)
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Proteus mirabilis , Pseudomonas , Enterobacter , Candida , Ilostridia species
Clinical Issues
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Extremely ill at presentation: Fever, flank pain, hyperglycemia, acidosis, dehydration, and electrolyte imbalance
Scanning Tips
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Gas in perinephric space or perinephric collections may obscure kidney
