Pyogenic liver abscess

A pyogenic liver abscess is a rare disease characterized by solitary/multiple collections of pus within the liver. The infection is caused by bacteria and is usually polymicrobial, with E. coli and K. pneumoniae being the common causative organisms. The majority of cases are caused by ascending infection from a biliary tract pathology (e.g., cholangitis due to choledocholithiasis, i.e. biliary strictures). Due to the liver's dual blood supply from the portal vein and the hepatic artery, an infectious focus in the gastrointestinal tract or bacteremia exposes the liver to high bacterial loads. Patients, typically middle-aged/elderly males, present with non-specific symptoms, such as fever, malaise, and weight loss. Right upper quadrant pain and tender hepatomegaly are specific features of a liver abscess but are often absent. Diagnosis is confirmed on abdominal imaging (ultrasound or CT), which demonstrates intrahepatic fluid-filled lesions with surrounding edema. Broad-spectrum IV antibiotics (ampicillin + sulbactam) and percutaneous/surgical drainage of the abscess cavity is the mainstay of treatment. Complications include sepsis, pneumonia, and abscess rupture into the peritoneum/thorax. Advancements in diagnostics and treatment have reduced the complications and mortality rates of pyogenic liver abscesses.

• Incidence: 2–3 cases per 100,000 people in the United States
• Peak incidence: 50–60 years
• Sex: slight male predominance

References:^[1][2][3][4]

Epidemiological data refers to the US, unless otherwise specified.

Risk factors

• Diabetes mellitus
• Hepatobiliary disease (e.g., cholelithiasis, transplant recipients, hepatic tumors)
• Pancreatitis
• Gastrointestinal malignancy (esp. colorectal carcinoma)
• Crohn's disease

Etiology by source

Microbiology

• Pyogenic liver abscess (80% of liver abscesses)
  • Polymicrobial infection (most common)
  • E. coli is the most common causative organism.
  • K. pneumoniae is the second most common.
  • Other causative bacteria: Enterococci, Streptococci, Staphylococcus aureus, Proteus vulgaris, anaerobes
• Non-pyogenic liver abscess
  • Fungal infection (< 10% of cases): Candida species (most common)
  • Amebic liver abscess; (< 10% of cases): Entamoeba histolytica

References:^{[1][2][5][6][7][8][9][10][11][12][13]}

• Classic triad of pyogenic liver abscess
  • Fever (with/without chills and rigors)
  • Malaise
  • Right upper quadrant pain
• Other symptoms
  • Anorexia and weight loss
  • Nausea and vomiting
  • Symptoms of diaphragmatic irritation
• Physical examination
  • Jaundice
  • Tender hepatomegaly
  • Intercostal tenderness
  • Epigastric tenderness
  • Decreased breath sounds in right lower lobe of the lung
  • Features of sepsis

The symptoms of pyogenic liver abscess are often non-specific (e.g., fever, weight loss, etc.).
References:^[1][2][6]

Laboratory tests

• Complete blood count: neutrophilic leukocytosis, normocytic normochromic anemia
• Liver function tests: : ↑ alkaline phosphatase (90%), ↑ AST and ALT; , hypoalbuminemia, hyperbilirubinemia
• Inflammatory markers: ↑ ESR and CRP
• Blood culture: positive in ∼ 50% of cases

Imaging

• Abdominal imaging is a confirmatory test for pyogenic liver abscess
• Abdominal ultrasound (US): seen as solitary/multiple, poorly demarcated, fluid-filled, round hypoechoic lesion(s) within the hepatic parenchyma with surrounding edema and hyperemia .
• Abdominal CT scan: Findings are similar to those on abdominal ultrasound; a peripheral rim enhancement is seen on IV contrast administration.

Percutaneous aspiration and culture of the aspirate

• Both diagnostic and therapeutic (see “Treatment” section below)
• Performed under US or CT guidance
• Aspirated material is cultured to determine the organism and its antibiotic-susceptibility profile.

References:^{[1][2][6][13][14]}

Pyogenic liver abscesses need to be differentiated from other space-occupying lesions of the liver.

• Amebic liver abscess
• Hepatic echinococcosis (hydatid cyst of the liver)
• Hepatic cysts
• Benign liver tumors
• Hepatocellular carcinoma
• Liver metastases

References:^[15]

The differential diagnoses listed here are not exhaustive.

Pyogenic liver abscesses are generally treated with both IV antibiotics and percutaneous drainage of the abscess. Some patients may require surgical drainage.

Antibiotics

• Indicated in all cases
• Broad-spectrum IV antibiotics: ampicillin + sulbactam; piperacillin + tazobactam; 3^rd generation cephalosporin + metronidazole (until antibiotic susceptibility is available)

Drainage of the abscess cavity

• Indicated in nearly all cases of pyogenic liver abscess
• Indication for percutaneous drainage/needle aspiration: solitary abscess
  • Small (< 5 cm) abscess: percutaneous needle aspiration
  • Large (> 5 cm) abscess: percutaneous drainage and intracavitary catheter placement
  • If percutaneous drainage/aspiration fails, a second attempt at percutaneous drainage/aspiration can be made before abscess will require surgical drainage.
• Indications for surgical drainage (open/laparoscopic)
  • Multiple or loculated abscesses
  • Deep-seated abscess not amenable to percutaneous drainage
  • Ruptured abscess
  • Thick viscous pus which cannot be drained percutaneously
  • Underlying disease which requires surgical intervention (e.g., choledocholithiasis, appendicitis, etc.)
• Contraindications: coagulopathy (e.g., international normalized ratio (INR) > 1.5; thrombocytopenia due to sepsis)

The underlying etiology (e.g, choledocholithiasis, biliary stricture, etc.) should also be treated to prevent recurrent pyogenic liver abscesses.
References:^{[1][6][16][17]}

• Rupture
  • Into the abdomen → peritonitis
  • Into the chest → empyema
  • Into the retroperitoneum → retroperitoneal abscess
• Sepsis
• Pneumonia
• Pleural effusion

References:^{[1][6][18][19]}

We list the most important complications. The selection is not exhaustive.

• Mortality rates
  • Untreated pyogenic liver abscess: 100%
  • With treatment: ∼12 %
• Poor prognostic factors
  • Pyogenic abscess with sepsis
  • Advanced age (> 70 years)
  • Multiple abscesses
  • Polymicrobial infection; anaerobic infection
  • Immunosuppression (e.g., malignancy, diabetes)
  • Need for surgical drainage

References:^[1][20][21]

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