Gas-forming upper UTI involving renal parenchyma &/or perinephric space

Highly echogenic areas within renal sinus and parenchyma with “dirty” shadowing

Ring-down artifacts: Air bubbles trapped in fluid

Perinephric fluid collections may be seen

Type I (33%): Parenchymal replacement by gas, ± crescent of subcapsular or perinephric gas

Type II (66%): Renal or perirenal fluid abscesses with bubbly gas pattern ± gas within renal pelvis

Evaluation for psoas abscess and spinal osteomyelitis essential

CT may help further delineate location and extent of renal and perirenal gas

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

Single or mixed organism(s) infection

Escherichia coli (68%), Klebsiella pneumoniae (9%)

Proteus mirabilis , Pseudomonas , Enterobacter , Candida , Ilostridia species

Extremely ill at presentation: Fever, flank pain, hyperglycemia, acidosis, dehydration, and electrolyte imbalance

Gas in perinephric space or perinephric collections may obscure kidney