Introduction

Liver abscesses can result from bacterial infection (pyogenic abscess) or from Entamoeba histolytica. Pyogenic abscesses have a high mortality rate of 40%. 

Liver abscesses generally result from spread of infection from the digestive tract via the portal vein, from biliary disease or by direct extension from an adjacent infection. 

Risk factors include:

• Biliary disease
• Trauma
• Diabetes
• Malignancy. 

Aetiology of liver abscess

Pyogenic liver abscess is frequently polymicrobial. Enteric Gram-negative bacilli (aerobes and anaerobes) are frequently cultured.  Many of the causative organisms originate in the gastrointestinal tract:

• Escherichia coli
• Klebsiella pneumoniae
• Bacteroides spp.
• Enterococcus spp.
• Anaerobic Streptococcus spp.
• Streptococcus ‘milleri’ group.

If the infection does not originate in the gastrointestinal tract, possible organisms are:

• Staphylococcus spp.
  • Staphylococcus aureus infection may be seen as a feature of disseminated staphylococcal sepsis, with metastatic lesions present at a number of sites
• Haemolytic Streptococcus spp.
• Streptococcus ‘milleri’ group (may prove difficult to treat, particularly if multiple lesions are present)

In immunosuppressed patients, fungi and opportunistic organisms are found.

Pyogenic abscesses can be either single or multiple; the latter are more common after systemic bacteraemia and are associated with a high mortality.

Entamoeba histolytica also leads to hepatic abscess and arises from a gastrointestinal infection: it is very common in developing countries.

Diagnosis of liver abscess

Clinical

Pyogenic abscess can present acutely from systemic bacteraemia or biliary tract infection.

Sub-acute presentation often results from a single abscess from a localised infection: the patient may be admitted to hospital with the symptoms of the primary infection (eg. appendicitis).

Signs and symptoms include:

• Fever
• Anorexia
• Nausea
• Weight loss
• Weakness
• Upper right quadrant pain
• Jaundice is rare until a late stage of the infection.

Laboratory diagnosis

Diagnostic investigations include:

• Culture of aspirated material (under ultrasound guidance) is the most useful diagnostic test
• With the advent of modern systems and improved media, particularly for the recovery of anaerobic organisms, blood culture is often helpful.

Imaging

• CT is the most useful imaging technique, with ultrasound effective for lesions more than a couple of centimetres in diameter.

Amoebic liver abscess

Positive serology for Entamoeba histolytica is indicative of amoebic rather than bacterial abscess, especially if there is a history of travel, age <50 and acute onset.  Negative faecal microscopy does not exclude liver disease.

There is usually a single abscess and 80% of these affect the right lobe of the liver.  True pus is absent: there is sterile pus and reddish-brown necrotic liver tissue, usually liquid.  This material does not contain the organism, but this can sometimes be found at the edge of the abscess. 

Ultrasound can be used to demonstrate the abscess.

Management of liver abscess

Mortality was formerly very high, but has been greatly improved by the combination of adequate drainage — the key step in cure — and antimicrobial chemotherapy. 

Drainage (needle aspiration or catheter) should always be performed.

Antibiotic rationale for pyogenic abscess

As mortality is high in patients with pyogenic abscess, empirical antibiotic therapy should be broad-spectrum, IV and in high doses.  Combinations of agents are required to cover the wide range of possible pathogens including Escherichia coli, Klebsiella pneumoniae, Bacteroides, Enterococcus spp., and anaerobic Streptococcus spp., penetrate the abscess cavity, and offer bactericidal activity.

Empirical therapy

Empirical therapy should be started immediately and suitable regimens include:

• An aminopenicillin (such as amoxicillin) plus a quinolone (such as ciprofloxacin) plus metronidazole

  or

• In the elderly or those with renal impairment: a penicillin (such as amoxicillin) plus an injectable cephalosporin (such as cefotaxime or cefuroxime) plus metronidazole.
• In penicillin-allergic patients: ciprofloxacin plus clindamycin.

Once the sensitivity results are known, antibiotic therapy should be amended accordingly. Duration of therapy is usually from 2–4 weeks or longer depending on number of abscesses and the clinical response.

Antibiotic therapy for amoebic liver abscess

Metronidazole for 5–10 days is effective for Entamoeba histolytica amoebic abscesses.  Although drainage may be required, amoebic abscesses are less likely than pyogenic abscesses to require drainage.  Diloxanide furoate is given for 10 days after the metronidazole to destroy cysts in the intestine to prevent reinfection.

Large abscesses and those that do not respond to treatment, particularly if rupture appears likely, require drainage by needle aspiration.  If this is not successful, surgical drainage may be required.