Pyogenic Liver Abscess (PLA)

Definition and Epidemiology

• Fischer's Mastery of Surgery, 8th ed.
• Maingot's Abdominal Operations

Routes of Infection / Pathogenesis

• Fischer's Mastery of Surgery; Yamada's Textbook of Gastroenterology, 7th ed.; Sleisenger & Fordtran's GI and Liver Disease

Risk Factors

• Diabetes mellitus
• Malnutrition, immunosuppression
• Prior hepatobiliary/pancreatic disease
• Liver transplant
• Cirrhosis
• History of biliary-intestinal anastomosis or sphincterotomy
• Regular PPI use
• IBD, colorectal malignancy
• Oral flora / periodontal disease (especially in alcoholics - cryptogenic cases)

Microbiology

• E. coli and Klebsiella pneumoniae - most frequently isolated
• Klebsiella pneumoniae (hypervirulent/mucoid) - a distinct syndrome, predominantly in Asia (accounts for ~80% of cases in Taiwan), community-acquired, associated with diabetes, and carries a high risk of metastatic complications (endophthalmitis, meningitis, necrotizing fasciitis)
• Streptococcus milleri group (S. anginosus, S. constellatus, S. intermedius) - normal GI flora, important cause
• Bacteroides fragilis, Fusobacterium necrophorum - most common anaerobes
• Staphylococci - post-trauma/instrumentation or hematogenous; prompt evaluation for infective endocarditis
• Proteus, Pseudomonas spp.
• Rare: Yersinia, Pasteurella, Haemophilus, Listeria, Actinomyces, Clostridium

• Sleisenger & Fordtran's; Fischer's Mastery of Surgery

Clinical Features

• Fever (most consistent finding; can be low-grade)
• Right upper quadrant or epigastric pain - may be pleuritic; may radiate to the right shoulder if the diaphragm is irritated
• Malaise, anorexia, weight loss, nausea
• Symptoms may be present 1 month or more before diagnosis
• Jaundice - uncommon; if present, suggests biliary obstruction
• Normochromic normocytic anemia, weight loss on exam
• Multiple abscesses (often biliary source) tend to present more acutely with sepsis/shock; solitary abscesses are more indolent

Imaging

Ultrasound (US)

• Early: mixed hypo/hyperechoic solid-appearing lesion
• Later: complex cystic mass with anechoic spaces and irregular wall, internal septations
• Gas-forming organisms: "dirty shadowing"
• No intracavitary Doppler flow (flow in periphery/septations only)

Ultrasound: pyogenic liver abscess appearing as a low-density collection with small internal echoes. (Maingot's Abdominal Operations)

CT (contrast-enhanced)

• Hypoattenuating mass with enhancing rim (most common appearance)
• "Double target sign" - central hypoattenuating pus cavity + enhancing inner rim + outer hypoattenuating rim of parenchymal edema
• "Cluster sign" - multiple small rim-enhancing lesions beginning to coalesce
• "Turquoise sign" - arborizing septa in K. pneumoniae abscess
• Gas within the abscess = gas-forming organism

MRI

• T1: hypointense center
• T2: hyperintense with perilesional edema
• DWI: restricted diffusion (bright DWI, dark ADC) - helpful to distinguish abscess from necrotic tumor
• Superior soft tissue contrast, but not always needed if US/CT is diagnostic

A: "Double target sign" on CT (arrowhead = enhancing rim, arrow = edematous outer ring). B: "Cluster sign" - coalescing small abscesses. C: K. pneumoniae abscess with internal gas. D: Color Doppler US showing avascular complex cystic lesion. (Fischer's Mastery of Surgery, 8th ed.)

Laboratory Findings

• Elevated alkaline phosphatase (common, often disproportionate)
• Elevated bilirubin, transaminases
• Leukocytosis
• Blood cultures positive in ~50% (up to 95% in K. pneumoniae PLA)
• Anemia
• Hypoalbuminemia in severe/chronic cases

Treatment

1. Antibiotics

• Draw blood cultures and aspirate abscess before starting antibiotics when possible
• Start broad-spectrum IV antibiotics empirically, covering gram-negatives, gram-positives, and anaerobes
• Classic regimens: aminoglycoside + clindamycin + ampicillin or vancomycin; fluoroquinolones can replace aminoglycosides; metronidazole can replace clindamycin
• Single-agent options: piperacillin-tazobactam, imipenem-cilastatin, or ticarcillin-clavulanate
• Note: K. pneumoniae is intrinsically resistant to ampicillin; first-generation cephalosporins lack adequate anaerobic coverage
• Duration: traditionally 4-6 weeks, though many studies support success with 2 weeks of IV therapy followed by oral step-down based on clinical/culture response
• Empiric anaerobic coverage should always be included in older patients and those with malignancy

2. Percutaneous Drainage

• Performed under US or CT guidance
• Either needle aspiration (single/repeat) or catheter drainage
• Catheter placement preferred for large, complex, or multiloculated abscesses
• Success rates are high; the method replaced open surgery as standard of care since the 1980s

• Coagulopathy
• Multiple small abscesses (microabscesses)
• Intervening vascular structures (e.g., portal vessels blocking safe access)
• Ascites
• Need for transpleural drainage
• Abscesses requiring surgical source control

3. Surgical Drainage

• Failure of percutaneous drainage/antibiotics
• Need to treat the underlying intra-abdominal source surgically
• Multiple macroscopic abscesses not amenable to percutaneous approach
• Patient on steroids
• Concomitant ascites

• Maingot's Abdominal Operations; Fischer's Mastery of Surgery

Complications

• Sepsis - most common
• Pleural effusion / empyema
• Rupture into peritoneum (peritonitis, high mortality)
• Subphrenic abscess (controlled leak)
• Hemobilia
• Portal vein or hepatic vein thrombosis - can cause portal hypertension or Budd-Chiari syndrome
• Bacteremia with metastatic seeding

• Bacteremia in ~95% of cases
• Endophthalmitis (6-61%) - can occur after drainage; often results in permanent visual loss
• Meningitis, brain abscess, CNS complications
• Necrotizing fasciitis
• Septic pulmonary emboli
• DIC, acute renal failure
• Maingot's Abdominal Operations; Yamada's Gastroenterology

Prognosis / Poor Prognostic Factors

Key Distinctions from Amebic Abscess