Renal abscess

Background

Renal anatomy.

Perinephric space with exaggerated pararenal space to show retroperitoneal structures. Perinephric bridging septa are seen between the left kidney and the adjacent renal fascia.

• 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

Risk Factors

• Inadequately treated or delayed treatment of UTI or pyelonephritis
• Diabetes
• Renal calculi
• Ureteral obstruction
• Any underlying urinary tract abnormality
• Immunosuppression

Perinephric vs renal abscess

	Perinephric	Renal
Necrotic Area	Perinephric fat between the renal cortex and Gerota's fascia	Renal parenchyma
Cause	Pyelonephritis (majority)	Pyelonephritis (vast majority)
Risk of morbidity	Higher	Lower

Genitourinary infection

(1) Human urinary system: (2) kidney; (3) renal pelvis; (4) ureter; (5) urinary bladder (6) urethra.
Additional structures: (7) adrenal gland; (8) renal artery and vein; (9) inferior vena cava; (10) abdominal aorta; (11) common iliac artery and vein; (12) liver; (13) large intestine; (14) pelvis.

"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
  • Renal abscess
  • Perinephric abscess
• Ureteral
  • Infected urolithiasis
• Bladder
  • Acute cystitis ("UTI")
  • Chronic cystitis
• Urethra/periurethra
  • Urethritis
  • Prostatitis

Clinical Features

• Costovertebral, flank, lumbar, lower chest, or back pain
  • Usually unilateral
• Fever, especially if prolonged or after antibiotic initiation
• Nausea, vomiting
• UTI or pyelonephritis symptoms not improving with antibiotics

Complications

• Need for open surgical management or nephrectomy
• Renal failure
• Sepsis, bacteremia
• Emphysematous kidney
• Cortical abscesses can rupture and form perinephric abscesses

Differential Diagnosis

• UTI
• Pyelonephritis
• Renal cyst
• Renal cancer

Evaluation

CT showing a right renal abscess that has burst into the perinephric space (arrow), best appreciated as the soft tissue density interposed between the kidney and adjacent liver

.

• Labs
  • CBC, BMP, UA, lactate
  • Urine culture, blood cultures
    • Some studies have shown up to 66% will have + blood cultures
• Imaging
  • Renal ultrasound
    • Well-defined hypoechoic lesion with thick walls and usually with internal debris
  • CT

Management

• Antibiotics
  • Broad spectrum if unclear source
    • If urinary source cover typical urinary pathogens
      • Ceftriaxone 1g IV
      • Piperacillin-Tazobactam 4.5 g IV
    • If hematogenous spread considered, cover for MSSA and MRSA
      • Vancomycin 15-20mg/kg IV
• Percutaneous drainage
• Open surgical management if patient fails antibiotics/percutaneous drainage

Disposition

• Admission for IV antibiotics and drainage
  • Especially if elderly or elevated BUN or creatinine

References

• Dembry LM, Andriole VT. “Renal and Perirenal Abscesses” Infectious Disease Clinics North America: 11, 3, (Sept 1997).
• Getting GK, Shaikh N. “Renal Abscess” Journal of EM: 31, 1 (2006): 99-100.
• Judith E, Stapczynski J. Stephan. "Urinary Tract Infections” Tintinalli's Emergency Medicine: A Comprehensive Study Guide. 7th ed. New York: McGraw-Hill, 2011. 632.
• Yen DHT, et al. “Renal Abscess: Early Diagnosis and Treatment” Am J EM: 17, 2 (March 1999).
• Shu T, Green JM, Orihuela E. “Renal and Perirenal Abscesses in Patients with Otherwise Anatomically Normal Urinary Tracts” Journal of Urology: 172 (July 2004): 148-150.
• http://www.ncbi.nlm.nih.gov/pubmed/16798166