Jennifer E. Heckman, MD, MPH
Stephen Y. Nakada, MD, FACS
BASICS
DESCRIPTION
• Acute necrotizing infection of the renal parenchyma and perirenal tissues caused by gas-forming organisms
– Onset may be acute or insidious
– Course is potentially life threatening (mortality: 11–42%)
• 1st report in 1898
• >200 reported cases
EPIDEMIOLOGY
Incidence
• All documented cases in adults
– Most patients >60 yr old
• Female predominance (6:1)
• Bilateral cases, unusual but reported (L > R)
Prevalence
N/A
RISK FACTORS
• Diabetes mellitus (DM) (up to 95%)
– Especially with poor glycemic control
• Urinary tract obstruction
– Urinary calculi
– Papillary necrosis
– Neoplasm
• Immunosuppression
Genetics
N/A
PATHOPHYSIOLOGY
• Poorly understood
• Impaired host response allows microorganism proliferation
• Hypothesized that elevated tissue glucose levels provide substrate for microorganisms
– Bacterial fermentation of sugar produces carbon dioxide
– Low oxygen tension allows urinary tract infection to ascend
• E. coli is primary causative organism (70–90%)
– Klebsiella, Proteus, Streptococcus, and coagulase-negative Staphylococcus less common
– Candida, Entamoeba histolytica, and Aspergillus fumigatus are rare causes
ASSOCIATED CONDITIONS
• Alcohol abuse
• Diabetic ketoacidosis
• Immunocompromised states, including transplant patients
• Impaired renal function
• Malnutrition
• Urinary tract obstruction, including urinary calculi, papillary necrosis, or neoplasm
GENERAL PREVENTION
• Strict glycemic control in diabetes mellitus (DM)
• Adequate treatment of pre-existing pyelonephritis
• Prompt relief of urinary tract obstruction, if present
DIAGNOSIS
HISTORY
• Classic triad:
– Fever, chills
– Nausea, vomiting
– Flank pain and/or abdominal pain
• Urinary frequency/urgency, dysuria
• Malaise
• Altered mental status
• History of DM, urinary calculi, and/or immunocompromise
• Pneumaturia absent unless infection involves collecting system
PHYSICAL EXAM
• Pyrexia
• Abdominal or flank tenderness
• Crepitus over flank (rare)
• Lethargy, confusion, altered mental status
• Sepsis/shock (tachycardia, hypotension)
DIAGNOSTIC TESTS & INTERPRETATION
Lab
• Complete blood count (CBC)
– Leukocytosis
– Thrombocytopenia
• Basic metabolic panel (BMP)
– Hyperglycemia
– Elevated serum creatinine
• Urinalysis +/− urine culture
– Pyuria, bacteriuria, positive urine culture
• Blood cultures
– Bacteremia (isolated organism same as that in urine)
Imaging
• Abdominal radiograph may show tissue gas in parenchyma (nonspecific, low sensitivity)
• Renal ultrasound may show highly echogenic area with dirty shadowing
• Computed tomography (CT) is imaging modality of choice (most sensitive and specific)
– May see:
Absence of fluid or presence of streaky or mottled gas +/− bubbly and loculated gas in renal parenchyma, collecting system, and/or perirenal tissue
Rim-like or crescent-shaped gas distribution surrounding kidney
Gas in renal vein, inferior vena cava, or retroperitoneum
Urinary tract obstruction (seen in ∼25% of cases)
– Contrast not necessary for diagnosis (and may be contraindicated in renal impairment)
• Classification system (1)[B]:
– Class 1: Gas confined to collecting system
– Class 2: Gas confined to renal parenchyma without extension to extrarenal space
– Class 3A: Perinephric extension of gas or abscess
– Class 3B: Pararenal extension of gas or abscess (beyond Gerota’s fascia and/or extension to adjacent tissues)
– Class 4: Bilateral emphysematous pyelonephritis or emphysematous pyelonephritis in a solitary kidney
– Therapeutic and prognostic implications:
Class 1 and 2: Percutaneous drainage successful, low mortality
Class 3 and 4: Percutaneous drainage less successful, increased mortality
Diagnostic Procedures/Surgery
None, diagnosis is radiographic
Pathologic Findings
• Gross
– Multiple renal parenchymal abscesses with central, gas-filled region
– Foci of micro- and macroinfarctions
• Microscopic
– Glomerulosclerosis, arteriosclerosis, intrarenal vascular thrombi, or papillary necrosis
DIFFERENTIAL DIAGNOSIS
• Acute pyelonephritis
• Emphysematous cystitis
• Fistulous communication with gastrointestinal or respiratory tracts
• Iatrogenic (instrumentation of urinary tract)
• Necrotic renal tumor
• Pyonephrosis with urinary tract obstruction
• Renal abscess
• Xanthogranulomatous pyelonephritis
TREATMENT
ALERT
Emphysematous pyelonephritis is urologic emergency that requires prompt diagnosis and intervention to prevent morbidity and mortality.
GENERAL MEASURES
• Rapid supportive measures:
– Fluid resuscitation
– Correction of electrolyte imbalances
– Vasopressors as needed
– Usually requires ICU status
• Indwelling urethral catheter to maximize urinary tract drainage and monitor urine output.
MEDICATION
First Line
• Antimicrobial agents
– Broad-spectrum parenteral antibiotics initially (dosages assume normal renal function):
Ampicillin–sulbactam (1.5 g q6h)
Ticarcillin–clavulanate (3.1 g q6h)
Piperacillin–tazobactam (3.375 g q6h)
Meropenem (500 mg q8h)
Imipenem (500 mg q6h)
Doripenem (500 mg q8h)
– Narrow to culture-directed antibiotics
– At least 14 days of therapy
• Hyperglycemia management
– Insulin (intravenous or subcutaneous)
Second Line
N/A
SURGERY/OTHER PROCEDURES
• Percutaneous drainage
– Indicated if:
Affected kidney is functioning
Affected kidney is obstructed
Localized area of gas identified
– ≥14Fr catheter (may benefit from more than one catheter)
– CT guidance preferred
– In combination with antibiotic therapy reduces mortality rate
– Helps preserve renal function in affected kidney
• If clinical improvement with medical management and percutaneous drainage, may delay or avoid nephrectomy
• Nephrectomy
– Requires adequate resuscitation and stabilization preoperatively
– Immediate vs. delayed (elective) based on clinical course
– Indicated if:
Affected kidney is nonfunctioning and nonobstructed
Lack of clinical improvement with medical management and percutaneous drainage
– Consider if:
Presence of risk factors, including acute renal failure, thrombocytopenia, altered mental status, or shock
Gas limited to renal parenchyma (dry-type emphysematous pyelonephritis)
– Flank approach preferred
ADDITIONAL TREATMENT
Radiation Therapy
N/A
Additional Therapies
N/A
Complementary & Alternative Therapies
N/A
ONGOING CARE
PROGNOSIS
• Dependent on:
– Time to diagnosis and treatment
– Local extent of the infection
• Mortality greatest in those presenting with (2)[B], (3)[B]:
– Acute renal failure
– Thrombocytopenia
– Mental status changes
– Shock
• Recent meta-analysis demonstrated treatment-based mortality (4)[B]:
– Medical management alone: 50%
– Medical management + emergency nephrectomy: 25%
– Medical management + percutaneous drainage: 13.5%
COMPLICATIONS
• Perinephric abscess
• Renal insufficiency or failure
• Loss of renal unit
• Sepsis/shock
• Death
• Following procedural intervention:
– Bowel or vascular injury
– Wound infection
FOLLOW-UP
Patient Monitoring
• Follow urine and blood cultures for growth and sensitivities for directed antibiotic therapy
• Follow-up CT (4–7 days postpercutaneous drainage) (5)[C]
– Look for other noncommunicating air/fluid collections (insert additional catheters as needed)
– Maintain all drainage catheters until imaging demonstration of resolution
• Nuclear renal scan to assess degree of renal functional impairment and determine necessity of elective nephrectomy when patient stabilized
Patient Resources
http://www.emedicinehealth.com/urinary_tract_infections/article_em.htm
REFERENCES
1. Huang JJ, Tseng CC. Emphysematous pyelonephritis: Clinicoradiological classification, management, prognosis, and pathogenesis. Arch Intern Med. 2000;160(6):797–805.
2. Falagas ME, Alexiou VG, Giannopoulou KP, et al. Risk factors for mortality in patients with emphysematous pyelonephritis: A meta-analysis. J Urol. 2007;178:880–885.
3. Lin YC, Lin YC, Lin HD, et al. Risk factors of renal failure and severe complications in patients with emphysematous pyelonephritis—a single-center 15-year experience. Am J Med Sci. 2012;343(3):186–191.
4. Somani BK, Nabi G, Thorpe P, et al. Is percutaneous drainage the new gold standard in the management of emphysematous pyelonephritis? Evidence from a systematic review. J Urol. 2008;179:1844–1849.
5. Chen MT, Huang CN, Chou YH, et al. Percutaneous drainage in the treatment of emphysematous pyelonephritis: 10-year experience. J Urol. 1997;157:1569–1573.
ADDITIONAL READING
• Aswathaman K, Gopalakrishnan G, Gnanaraj L, et al. Emphysematous pyelonephritis: Outcome of conservative management. Urology. 2008;71(6):1007–1009.
• Shokeir AA, El-Azab M, Mohsen T, et al. Emphysematous pyelonephritis: A 15-year experience with 20 cases. Urology. 1997;49: 343–346.
• Ubee SS, McGlynn L, Fordham M. Emphysematous pyelonephritis. BJU Int. 2011;107(9):1474–1478.
See Also (Topic, Algorithm, Media)
• Diabetes Mellitus, Urologic Considerations
• Pyelonephritis, Acute, Adult
• Pyelonephritis, Chronic
• Pyelonephritis, Xanthogranulomatous
• Pyelonephritis, Emphysematous Image 
• Urosepsis
• Urinary Tract Infection (UTI), Adult Female
• Urinary Tract Infection (UTI), Adult Male
• Urinary Tract Infection (UTI), Complex, Adult
CODES
ICD9
• 250.40 Diabetes with renal manifestations, type II or unspecified type, not stated as uncontrolled
• 590.10 Acute pyelonephritis without lesion of renal medullary necrosis
• 599.60 Urinary obstruction, unspecified
ICD10
• E11.21 Type 2 diabetes mellitus with diabetic nephropathy
• N10 Acute tubulo-interstitial nephritis
• N13.9 Obstructive and reflux uropathy, unspecified
CLINICAL/SURGICAL PEARLS
• Must have high index of suspicion to diagnose this rare, potentially life-threatening condition promptly.
• Diagnosis made radiographically (CT most sensitive and specific).
• Outcomes most optimal with combination of fluid resuscitation, systemic antibiotics, and percutaneous drainage (with nephrectomy when indicated).