Pyogenic Liver Abscess

A pyogenic liver abscess is a localised collection of pus within the liver parenchyma caused by bacterial infection. It is a serious infection requiring both antimicrobial therapy and, in the majority of cases, drainage.

It arises through several recognised routes of spread:

• Biliary tract disease, the commonest source in many settings.
• Portal venous spread from an intra abdominal infective source.
• Haematogenous spread via the hepatic artery.
• Direct extension from a contiguous infective focus.
• In a proportion of cases, no identifiable source (cryptogenic).

Pathophysiology and microbiology

• Biliary tract obstruction (from gallstones, malignancy or stricture) with ascending cholangitis is a common source. It typically produces multiple, often bilobar abscesses.
• Portal venous spread (classically from appendicitis, diverticulitis or other intra abdominal sepsis) more typically produces a solitary abscess. It is most often in the right lobe, given its larger relative blood supply from the portal system.
• Polymicrobial infection with enteric organisms (Escherichia coli, Klebsiella pneumoniae, and anaerobes including Bacteroides species) is typical.
• Klebsiella pneumoniae, particularly a specific hypervirulent strain, is notably prevalent as a cause of monomicrobial pyogenic liver abscess in certain populations, particularly in parts of Asia. It is associated with a distinct clinical syndrome including a propensity for metastatic infection to the eye and central nervous system.
• Amoebic liver abscess, caused by Entamoeba histolytica, is an important alternative and clinically overlapping diagnosis with differing management. Consider it particularly with relevant travel or residence history in an endemic region.

• Fever, often with rigors, right upper quadrant pain, and malaise characterise the typical presentation, developing over days to a few weeks, with nausea, anorexia and weight loss frequently accompanying the more acute features in a more insidious presentation.
• Right upper quadrant tenderness, hepatomegaly, and, less commonly, jaundice (more prominent where biliary obstruction is the underlying cause) are typical examination findings, with a right sided pleural effusion or basal lung changes occasionally present, reflecting diaphragmatic irritation from the adjacent hepatic inflammatory process.
• Presentation can be more insidious, particularly in the elderly or immunocompromised, with non specific malaise and weight loss predominating over the more classical acute febrile picture, requiring a lower threshold for imaging in these groups.
• A relevant underlying source (recent biliary intervention, known gallstone disease, recent intra abdominal infection or surgery, or diabetes, which is a recognised risk factor particularly for the Klebsiella pneumoniae associated syndrome) should be actively sought in the history.

• Ultrasound or, with greater sensitivity and anatomical detail, contrast enhanced computed tomography of the abdomen confirms the diagnosis. It shows one or more hypoechoic (on ultrasound) or hypodense (on computed tomography) lesions within the liver parenchyma.
• Computed tomography is additionally valuable for identifying the underlying biliary or intra abdominal source where present.
• Obtain blood cultures in every case. They are positive in a substantial proportion of cases even where percutaneous sampling has not yet been performed.
• Where drainage is performed, culture of the aspirated pus gives the definitive microbiological diagnosis and guides targeted antibiotic therapy.
• Full blood count typically shows a marked leucocytosis. Liver function tests frequently show a cholestatic pattern with elevated alkaline phosphatase. Inflammatory markers are elevated. All of these support the diagnosis and help monitor treatment response.
• Distinguishing pyogenic from amoebic abscess is clinically important, given differing treatment approaches.
• Amoebic abscess is more likely to be solitary and located in the right lobe, with a relevant travel or residence history in an endemic region. Leucocytosis is typically less marked than in pyogenic abscess.
• Serological testing for Entamoeba histolytica confirms amoebic abscess. It is positive in the large majority of cases.

• Percutaneous image guided drainage is indicated for abscesses generally larger than 3 to 5 cm. Use needle aspiration or, more commonly for larger abscesses, catheter placement with continued drainage.
• Drainage provides source control and a definitive microbiological diagnosis through culture of the aspirated material.
• Start empirical broad spectrum intravenous antibiotic therapy promptly alongside drainage, covering enteric Gram negative organisms and anaerobes. Adjust once culture and susceptibility results are available.
• A typical regimen is co amoxiclav 1.2 g intravenously three times daily. Alternatively, combine ceftriaxone 2 g intravenously once daily with metronidazole 500 mg intravenously three times daily.
• Consider piperacillin with tazobactam 4.5 g intravenously three times daily, or a carbapenem, for more severe presentations, healthcare associated infection, or where broader empirical Gram negative and anaerobic coverage is required pending culture results.
• Total antibiotic duration is typically prolonged, generally four to six weeks in total.
• Give an initial intravenous course, commonly two to three weeks, particularly where drainage has achieved adequate source control. Then transition to an appropriate oral agent for the remainder, guided by clinical, biochemical (inflammatory marker trend) and radiological response.
• Multiple small abscesses not individually amenable to percutaneous drainage may be managed with antibiotics without drainage. So may a solitary small abscess (generally under 3 cm) with good clinical response to antibiotics alone.
• Monitor closely for clinical and radiological response, with a low threshold to proceed to drainage if response is inadequate.
• Identification and definitive treatment of the underlying source is essential alongside treatment of the abscess itself. Examples are biliary drainage or stone extraction for obstructive biliary disease, and treatment of the primary intra abdominal source such as appendicitis or diverticulitis. Recurrence risk persists if the underlying predisposing pathology is not addressed.
• Surgical drainage is reserved for cases where percutaneous drainage has failed, where multiple loculated abscesses are not amenable to percutaneous approach, or where there is a specific indication for surgical management of the underlying source pathology.
• Where amoebic liver abscess is confirmed or strongly suspected from serology and epidemiological context, the primary treatment is metronidazole 750 mg orally or intravenously three times daily for seven to ten days.
• Drainage is generally unnecessary in the majority of amoebic cases. It is reserved for very large abscesses with risk of rupture, diagnostic uncertainty, or failure to respond to medical therapy alone.
• Follow metronidazole with a luminal agent such as paromomycin to eradicate any residual intestinal colonisation and prevent relapse.
• Use follow up imaging to confirm resolution. Radiological resolution frequently lags well behind clinical and biochemical improvement.
• Ongoing radiological abnormality alone, with clear clinical improvement, does not necessarily indicate treatment failure or the need for extended antibiotic duration beyond the standard course.