Rare clinical entity which can lead to delayed diagnosis
Usually a complication of a UTI or pyelonephritis
Most commonly due to E. Coli, Klebsiella, Proteus
Less often can be due to hematogenous spread from other sources of infection
Most commonly due to Staph aureus
Most commonly due to E. Coli, Klebsiella, Proteus
Most commonly due to Staph aureus
Inadequately treated or delayed treatment of UTI or pyelonephritis 
Diabetes
Renal calculi
Ureteral obstruction
Any underlying urinary tract abnormality
Immunosuppression
"UTI" frequently refers specifically to acute cystitis, but may also be used as a general term for all urinary infections; use location-specific diagnosis.
Renal/perirenal
Pyelonephritis
Emphysematous pyelonephritis<unk> 
Perinephric<unk> 
Ureteral
Infected urolithiasis
Bladder
Acute cystitis ("UTI")
Chronic cystitis
Urethra/periurethra
Urethritis
Prostatitis
Pyelonephritis
Emphysematous pyelonephritis<unk> 
Perinephric<unk> 
Emphysematous pyelonephritis
Infected urolithiasis
Acute cystitis ("UTI")
Chronic cystitis
Urethritis
Prostatitis
Renal abscess
UTI
Emphysematous pyelonephritis
Pyelonephritis
Renal cyst
Glomerulonephritis
Renal cancer
Perinephric abscess