Emphysematous Pyelonephritis

• Acute, fulminant, necrotizing infection of kidney and perirenal tissues associated with gas formation which may be life-threatening
• Organism
  • E. coli (vast majority of cases)
  • Klebsiella pneumoniae (9%)
  • Proteus mirabilis
  • Pseudomonas
  • Enterobacter
  • Candida
  • Clostridia (exceptionally rare)
• Predisposed
  • Especially diabetics in almost all cases
  • Immunocompromised patients
  • Ureteral obstruction
• Average age
  • Mid-fifties
  • Twice as common in females as males
• Clinical findings
  • Features of acute severe pyelonephritis (chills, fever, flank pain, lethargy, confusion) not responding to treatment
  • Positive blood and urine cultures (in majority)
  • Urosepsis
  • Shock
  • Fever of unknown origin and no localizing signs in almost 20%
• Frequently have multiple associated medical problems
  • Uncontrolled hyperglycemia
  • Acidosis
  • Dehydration
  • Electrolyte imbalance
• Location
  • Most are unilateral
  • 5-7% bilateral
• Types
  • Type I (33%)
    • Streaky or mottled gas in interstitium of renal parenchyma radiating from medulla to cortex
    • Crescent of subcapsular or perinephric gas
    • No fluid collection (= no effective immune response)
    • Prognosis in this type is poor (69% mortality)
  • Type II (66%)
    • Bubbly and/or loculated intrarenal gas (infers presence of abscess)
    • Renal and/or perirenal fluid collection
    • Gas within collecting system in almost all

Emphysematous Pyelonephritis. Two axial CT scans of abdomen and pelvis show air within
collecting system of kidney in top image with air and debris in bladder lumen and wall in bottom image

• Prognosis in this type is much better (18% mortality)
• Parenchymal destruction absent
• Decreased contrast excretion (due to compromised renal function)

• CT findings
  • Most reliable and sensitive modality
  • Mottled areas of low attenuation extending radially along the pyramids
  • Extensive involvement of kidney and perinephric space
  • Air extending through Gerota’s fascia into retroperitoneal space
  • Occasionally gas in renal veins
• Ultrasound findings
  • High-amplitude echoes within renal sinus and/or renal parenchyma associated with "dirty" shadowing
    • "Comet tail" reverberations
  • Kidney may be completely obscured by large amount of gas in perinephric space (DDx: surrounding bowel gas)
  • Gas may be confused with renal calculi
• MR findings
  • Signal void on T1WI and T2WI (DDx: renal calculi, rapidly flowing blood)
• DDx
  • Emphysematous pyelitis (gas in collecting system but not in parenchyma, diabetes in 50%, less grave prognosis)
• Treatment
  • Antibiotic therapy and nephrectomy
  • Drainage procedure with coexisting obstruction
• Mortality
  • 60-75% under antibiotic treatment
  • 21-29% after antibiotic treatment and nephrectomy
  • 80% with extension into perirenal space