Pyogenic Abscess

Joseph Misdraji, MD

Key Facts

Etiology/Pathogenesis

Most commonly isolated organisms are Escherichia coli, Klebsiella pneumonia, Enterococcus spp., Streptococcus spp., and Pseudomonas spp.
Anaerobes are isolated in up to 25% of cases
Fungi, such as Candida and Aspergillus, are found in 15% of cases
At least 1/3 of cases are polymicrobial

Clinical Issues

Major causes include biliary disease and intraabdominal infection
Risk factors: Diabetes mellitus, malignancy, alcohol abuse, cirrhosis, hypertension, recent surgery, and immunosuppression
Percutaneous drainage and antibiotics are mainstay of therapy
Main risk factors for metastatic infection are diabetes mellitus and infection with K. pneumonia
Mortality ranges from 5-31%

Macroscopic Features

Microscopic Pathology

Abundant neutrophils, fibrin, and bile
Aerobic and anaerobic culture of abscess contents and histochemical stains for organisms are required to determine cause

Gross photograph of a hepatectomy specimen shows large, irregular, yellow-tan soft abscesses with central green bile-stained necrosis.

Whole mount of a paraffin section of liver abscesses shows irregular necrotic lesions

with bile and inflammation. Another abscess is present at the top of the section

TERMINOLOGY

Definitions

ETIOLOGY/PATHOGENESIS

Infectious Agents

Most commonly isolated organisms: Escherichia coli, Klebsiella pneumonia, Enterococcus spp., Streptococcus spp., and Pseudomonas spp.
- Organisms that produce formic hydrogenylase (Klebsiella spp. and E. coli) can convert acids in abscess into carbon dioxide and hydrogen gas
  - Gas-forming pyogenic abscess carries higher risk of septic shock, bacteremia, and death
Anaerobes are isolated in up to 25% of cases
- Most commonly microaerophilic Streptococci, Bacteroides fragilis, Fusobacterium necrophorum, and Clostridia spp.
- Actinomyces spp. can be associated with formation of sinus tracts
Rare isolates include Francisella tularensis, Burkholderia pseudomallei (cause of melioidosis), Brucella spp. (particularly B. suis), and Listeria monocytogenes
Fungi, such as Candida and Aspergillus, are found in 15% of cases
At least 1/3 of cases are polymicrobial

Predisposing Conditions

Historically associated with acute appendicitis or intraabdominal infection, particularly in children
Biliary disease has emerged as most common etiology

CLINICAL ISSUES

Epidemiology