Diagnostic Ultrasound - Abdomen and Pelvis

Emphysematous Pyelonephritis
TERMINOLOGY
Abbreviations
• Emphysematous pyelonephritis (EPN)
Definitions
• Gas-forming upper urinary tract infection involving renal
parenchyma &/or perinephric space
IMAGING
General Features
• Location
○ Unilateral > bilateral (5-7% of cases)
Ultrasonographic Findings
• Grayscale ultrasound
○ Highly echogenic areas within renal sinus and
parenchyma with "dirty" shadowing
○ Ring-down artifacts: Air bubbles trapped in fluid
○ Gas in perinephric space or perinephric collections may
obscure kidney
• Color Doppler
○ Twinkling artifact: May mimic stones
Radiographic Findings
• Radiography
○ Gas in parenchyma ± perinephric space
CT Findings
• 2 types of emphysematous pyelonephritis
○ Type I (33%): Parenchymal replacement by gas,±
subcapsular or perinephric gas
○ Type II (66%): Renal or perirenal abscesses with gas, ± gas
within renal pelvis
• Intraparenchymal, intracaliceal, and intrapelvic gas
• Gas may extend into subcapsular, perinephric, pararenal,
contralateral retroperitoneal spaces
MR Findings
• T1WI, T2WI: Foci of gas are signal voids on all sequences
• T2WI:Perinephric edema ± fluid collections
Imaging Recommendations
• Best imaging tool
○ CT is ideal to determine location and extent of renal and
perirenal gas
○ Evaluation for psoas abscess and spinal osteomyelitis is
essential
DIFFERENTIAL DIAGNOSIS
Renal Calculus
• Discrete echogenic focus with sharp distal acoustic
shadowing
Nephrocalcinosis
• Generalized increased echogenicity of renal pyramid ±
shadowing
Papillary Necrosis
• Single or multiple cystic cavities in medullary pyramids
continuous with calyces
• Sloughed papillae: Echogenic, nonshadowing
Emphysematous Pyelitis
• Gas limited to renal collecting system and pelvis, not
parenchyma
• Usually less clinically serious than EPN
Benign Gas in Renal Pelvis
• May arise from recent interventions
PATHOLOGY
General Features
• Etiology
○ Single or mixed organism(s) infection
– Escherichia coli (68%), Klebsiella pneumoniae (9%)
– Proteus mirabilis, Pseudomonas, Enterobacter, Candida,
Ilostridia species
○ Risk factors
– Recurrent or chronic UTIs
– Immunocompromised: Diabetes mellitus (87-97%)
– Ureteral obstruction (20-40%): Calculi, stenosis
○ Pathogenesis
– Pyelonephritis → ischemia and low oxygen tension →
anaerobe proliferation in anaerobic environment →
CO2 production
Gross Pathologic & Surgical Features
• Suppurative necrotizing infection of renal parenchyma and
perirenal tissue with multiple cortical abscesses
CLINICAL ISSUES
Presentation
• Most common signs/symptoms
○ Extremely ill at presentation: Fever, flank pain,
hyperglycemia, acidosis, dehydration, and electrolyte
imbalance
○ Hypoalbuminemia and need for emergent hemodialysis
are independent predictors of mortality
Natural History & Prognosis
• Complications: Generalized sepsis
• Prognosis: Poor
○ Mortality: 66% with type I, 18% with type II
Treatment
• Antibiotic therapy; nephrectomy for type I
○ Conservative management fails in at least 1/3 of cases
• CT-guided drainage procedures for type II
SELECTED REFERENCES
1. Lu YC et al: Predictors of failure of conservative treatment among patients
with emphysematous pyelonephritis. BMC Infect Dis. 14:418, 2014
2. Lin YC 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. 343(3):186-91, 2012
3. Chen KC et al: The role of emergency ultrasound for evaluating acute
pyelonephritis in the ED. Am J Emerg Med. 29(7):721-4, 2011
4. Ubee SS et al: Emphysematous pyelonephritis. BJU Int. 107(9):1474-8, 2011
5. Grayson DE et al: Emphysematous infections of the abdomen and pelvis: a
pictorial review. Radiographics. 22(3):543-61, 2002
Diagnoses: Urinary Tract
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