What are the causes and pathophysiology of liver abscess?

Causes and Pathophysiology of Liver Abscess

Causal Organisms

Pyogenic (Bacterial) Liver Abscess

Gram-negative organisms, particularly Escherichia coli and Klebsiella pneumoniae, are the most frequent bacterial isolates in pyogenic liver abscesses, with K. pneumoniae showing increasing incidence worldwide. 1

• Gram-positive organisms including Staphylococcus and Streptococcus species (particularly abscess streptococci) are also important pathogens. 1, 2
• Anaerobic bacteria frequently contribute to polymicrobial infections. 1, 2
• Hypervirulent clones of Klebsiella pneumoniae harboring specific virulence factors have emerged predominantly in Asian countries and are spreading to the USA, Australia, and Europe, requiring special alertness. 3
• Fusobacterium nucleatum from dental sources represents a rare cause, particularly in patients with poor oropharyngeal hygiene. 4

Parasitic Liver Abscess

In South-East Asia, Africa, and tropical/subtropical regions with poor sanitation, Entamoeba histolytica is the most common cause of hepatic abscess. 1

• E. histolytica is transmitted via the fecal-oral route, colonizes the gastrointestinal tract, and spreads extraintestinally to the liver. 1
• Echinococcal (hydatid) cysts can become secondarily infected or leak and should be considered in patients from the Middle East, Central Asia, and the Horn of Africa. 1

Fungal and Rare Causes

• Mycobacteria species, Nocardia species, and other fungal organisms should be considered in immunosuppressed hosts. 1
• Candida species, Pseudomonas aeruginosa, and Staphylococcus aureus are uncommon and only detected in specific contexts. 2

Pathophysiology and Routes of Infection

Mechanisms of Hepatic Contamination

Microbial contamination of the liver parenchyma occurs via four principal routes: biliary, portal venous, arterial hematogenous, or direct extension by contiguity. 5

Biliary Route (Most Common in Western Countries)

• Lithiasic biliary disease including cholecystitis and cholangitis represents a major source. 5
• Chronic enteric biliary contamination from sphincterotomy or bilioenteric anastomosis predisposes to abscess formation. 5
• Biliary obstruction with ascending infection allows bacterial translocation into hepatic parenchyma. 5

Portal Venous Route

Pyogenic liver abscesses are often polymicrobial, reflecting gut flora translocation through the portal route. 1

• Intra-abdominal infections including appendicitis, sigmoid diverticulitis, and Crohn's disease seed the liver via portal circulation. 5
• Infections in the drainage area of the portal vein typically produce mixed flora consisting of gram-negative aerobes and anaerobic bacteria. 6

Arterial Hematogenous Route

• Systemic septicemia can seed the liver, occurring on either healthy liver or preexisting liver diseases (biliary cysts, hydatid cysts, cystic or necrotic metastases). 5
• Abscesses secondary to systemic sepsis typically contain Staphylococci or Streptococci. 6
• The temporal relationship between dental procedures and abscess development suggests hematogenous seeding from oropharyngeal sources. 7, 4

Direct Extension

• Contiguous spread from adjacent infected structures can directly contaminate hepatic parenchyma. 5

Iatrogenic and Post-Procedural Causes

• Bile duct ischemia secondary to pancreatoduodenectomy or liver transplantation. 5
• Interventional techniques including radiofrequency ablation and intra-arterial chemoembolization. 5
• Liver trauma. 5
• Post-procedural cholangiolytic abscesses can develop after ERCP or sphincterotomy, typically presenting as small, multiple lesions. 7

Special Pathophysiologic Considerations

Substantial stenosis of the celiac trunk should be detected before performing pancreatoduodenectomy to help avoid iatrogenic hepatic abscess. 5

• The presence of chronic enteric biliary contamination (sphincterotomy, bilioenteric anastomosis) should be determined before performing radiofrequency ablation or chemoembolization. 5
• K. pneumoniae abscesses can give rise to distant septic metastases due to hypervirulent strains. 5

Geographic and Epidemiologic Patterns

• In industrialized Western countries, pyogenic liver abscess accounts for over 80% of cases. 3
• Entamoeba histolytica is responsible for up to 10% of cases globally, with higher incidence in tropical areas. 3
• The spectrum of causative microorganisms varies across the world and is changing due to increasing worldwide travel activity. 2