Liver Abscess

Pyogenic liver abscesses (PLAs)

• Most common type, especially in developed countries, accounting for ~80% of cases.
• Typically polymicrobial.
• Common sources include:
  • Biliary tract infections (e.g. ascending cholangitis).
  • Portal vein seeding from intra-abdominal sources (e.g. appendicitis, diverticulitis).
  • Haematogenous spread via the hepatic artery (e.g. from endocarditis or sepsis).
  • Direct extension from contiguous infections (e.g. subphrenic abscess).
  • Penetrating trauma or postoperative contamination.

Amoebic liver abscesses (ALAs)

• Caused by Entamoeba histolytica.
• Account for ~10% of liver abscess cases worldwide.
• More common in tropical and subtropical regions.
• Typically solitary and located in the right hepatic lobe.
• Result from haematogenous spread of trophozoites from the colon via the portal vein.

Fungal liver abscesses

• Rare, occurring primarily in immunocompromised individuals.
• Seen in patients with neutropenia, haematologic malignancy, or those undergoing chemotherapy.
• Candida species are the most common fungal pathogens.

Pyogenic Liver Abscess (PLA)

Polymicrobial nature

• Most pyogenic liver abscesses are polymicrobial.
• Common aerobic bacteria include Escherichia coli, Klebsiella pneumoniae, Streptococcus species (particularly the Streptococcus anginosus group: S. constellatus, S. anginosus, S. intermedius), Enterococcus species, Staphylococcus aureus, and Pseudomonas species.
• Klebsiella pneumoniae is becoming increasingly prominent globally, especially in Southeast Asia. It is strongly associated with monomicrobial abscesses, diabetes mellitus, and underlying colorectal cancer. Hypervirulent strains may lead to metastatic infections, including endophthalmitis and central nervous system involvement.
• Staphylococcus aureus is more commonly seen in cases involving haematogenous spread, such as endocarditis.
• Pseudomonas species are less frequently encountered but can be involved.

Anaerobes

• Anaerobic bacteria were historically under-recognised in PLAs but are now more frequently identified due to improved culturing techniques.
• Common anaerobes include Bacteroides fragilis, Fusobacterium necrophorum, and anaerobic or microaerophilic Streptococcus species.

Unusual bacterial pathogens

• Less commonly isolated organisms include Salmonella typhi, Yersinia enterocolitica, Actinomyces species, Eikenella corrodens, and Brucella melitensis.
• Salmonella typhi is particularly seen in patients with recurrent pyogenic cholangitis.
• A small case series from Taiwan described PLA as a presenting feature of hepatocellular carcinoma, especially in endemic regions.

Sources of infection

• Biliary tract disease, such as gallstones, biliary strictures, malignancy, or congenital anomalies, is now the most common cause of pyogenic liver abscess.
• Cholangitis is implicated in approximately 50% of cases.
• Other routes of infection include seeding via the portal vein from abdominal infections (e.g. diverticulitis, appendicitis), haematogenous spread through the hepatic artery, direct extension from contiguous infections (e.g. cholecystitis), and penetrating abdominal trauma.
• Some cases are classified as cryptogenic, with no identifiable source found despite thorough investigation.

Amoebic Liver Abscess (ALA)

• Amoebic liver abscesses are caused by Entamoeba histolytica, a protozoan parasite.
• Infection typically begins in the colon, resulting in amoebic colitis, with trophozoites migrating to the liver via the portal circulation.
• ALAs are usually solitary and preferentially located in the right hepatic lobe.

Epidemiology

• Amoebic liver abscesses are rare in developed countries but are frequently observed in immigrants or returning travellers from endemic areas such as South Asia, Africa, and Central or South America.

Fungal Liver Abscess

Causative organisms

• Fungal liver abscesses are primarily due to Candida albicans.
• In rare cases, Aspergillus species may be involved.

At-risk populations

• These abscesses typically occur in immunocompromised individuals.
• Risk factors include prolonged broad-spectrum antibiotic use, haematologic malignancies, solid-organ transplantation, and both congenital and acquired immunodeficiency states.

Parasitic Liver Abscess – Hydatid Disease

Cause and transmission

• Parasitic liver abscess due to hydatid disease is caused by the larval form of Echinococcus granulosus, a cestode in the family Taeniidae.
• The infection is transmitted via the faecal–oral route through ingestion of food or water contaminated with eggs from infected dogs.

Clinical features

• The liver is the most common site of hydatid cyst development.
• Patients may present with hepatomegaly, non-specific abdominal discomfort, or the cysts may be incidentally discovered during imaging.
• Hydatid cysts enlarge slowly and often do not produce symptoms until late in the disease course.

Routes of Infection and Mechanisms of Spread

Biliary Tree (Most Common Route)

• Biliary obstruction—due to gallstones, malignancy, strictures, or congenital anomalies—can cause ascending infection.
• Indwelling biliary stents or post-surgical complications may act as sources for solitary abscesses.
• Stasis of bile flow permits bacterial proliferation and translocation into hepatic parenchyma.

Portal Vein

• Infections from intra-abdominal organs such as the bowel, pancreas, or gallbladder can lead to septic thrombophlebitis.
• Conditions like appendicitis, diverticulitis, or inflammatory bowel disease may trigger pylephlebitis, releasing septic emboli into the portal circulation.
• These emboli are filtered by hepatic sinusoids and act as foci for microabscess formation, which may coalesce into solitary lesions.

Hepatic Artery

• Haematogenous dissemination from systemic infections (e.g. endocarditis, pyelonephritis) may result in microabscesses.
• This is more common in immunocompromised individuals and patients with bacteraemia.

Contiguous Spread

• Infections from adjacent structures (e.g. perforated bowel, subphrenic abscess) can directly invade liver tissue.

Penetrating and Blunt Trauma

• Penetrating injuries may directly introduce pathogens into the liver.
• Blunt trauma can result in haematoma, necrosis, and bile leakage, creating an environment conducive to secondary infection.

Procedural and Iatrogenic Sources

• Liver abscess may arise after procedures such as:
  • Percutaneous ablation or chemoembolisation of hepatic tumours
  • Liver transplantation
  • Endoscopic biliary sphincterotomy
  • Hepatic cryotherapy
• Instrumentation of the biliary tract is an increasingly recognised risk factor.

Anatomical Considerations

• The right hepatic lobe is affected more frequently than the left, in approximately a 2:1 ratio.
• This may be due to:
  • Greater volume of hepatic tissue
  • Richer blood supply via the superior mesenteric and portal veins
  • Denser network of biliary canaliculi
  • Proposed ‘streaming effect’ of portal blood flow directing pathogens preferentially to the right lobe
• Bilateral involvement is seen in approximately 5% of cases.

Host Factors and Underlying Conditions

• Immunocompromised states (e.g. diabetes mellitus, haematologic malignancy, chronic granulomatous disease, cirrhosis)
• Previous liver transplant
• Hepatic neoplasms (both primary and secondary)
• Cardiopulmonary disease
• Poor dental hygiene, possibly linked to cryptogenic bacteraemia

Other Contributing Factors

• Approximately 40% of liver abscesses are considered cryptogenic, where no definitive source of infection is found despite investigation.
• Secondary infection of existing hepatic lesions (e.g. amoebic abscesses, hydatid cysts, tumours) may also lead to pyogenic liver abscess.
• Rare causes include foreign body ingestion leading to perforation and migration into the liver.

Historical Perspective

• Historically, appendicitis was the predominant cause of liver abscess, but its incidence has significantly declined with advances in early diagnosis and management.
• In contemporary settings, biliary tract pathology is the most common identifiable aetiology.

Global Incidence and Regional Variation

• In the United Kingdom and the United States, the estimated annual incidence is approximately 2.3 to 3.6 cases per 100,000 population.
• The frequency among hospitalised patients ranges from 8 to 20 cases per 100,000 hospital admissions, with some studies noting a modest but steady increase in incidence.

Regional Differences

• Higher incidence rates have been reported in East and Southeast Asia, particularly Taiwan, where the annual incidence has reached 15–17.6 per 100,000.
• This elevated rate has been attributed to the rise in pyogenic abscesses due to Klebsiella pneumoniae, often in association with diabetes and hepatobiliary infections.

Amoebic Abscesses

• Entamoeba histolytica infection, the cause of amoebic liver abscess, is endemic in Central and South America, Africa, and Asia.
• In developed countries, amoebic abscesses are primarily observed in immigrants and travellers from endemic areas.

Demographics and Risk Stratification

Age

• The incidence of liver abscess increases with advancing age, with most cases now occurring in individuals in their sixth and seventh decades.
• Historically, abscesses were more prevalent in the fourth and fifth decades, especially as complications of appendicitis.
• A small peak in incidence is seen during the neonatal period, usually associated with umbilical vein catheterisation and sepsis.
• In children and adolescents, liver abscesses are rare and often linked to underlying immunodeficiency, trauma, or severe malnutrition.

Sex

• While some data suggest a higher prevalence in males, particularly for pyogenic liver abscesses, more recent studies indicate that sex predilection has diminished.
• However, males may have a poorer prognosis once hepatic abscesses develop.

Trends Over Time

Historical Data

• Autopsy series from the late 19th to mid-20th century show consistent findings: 0.7% (1896–1933), 0.45% (1934–1958), and 0.57% (1959–1968) of autopsies revealed liver abscesses.
• Despite stable or slightly rising incidence rates, mortality has declined, likely due to better imaging, earlier diagnosis, percutaneous drainage techniques, and improved critical care.

Pyogenic Liver Abscess (PLA)

• PLAs represent a major proportion of liver abscesses in developed regions, accounting for approximately 50% of all visceral abscesses and 13% of intra-abdominal abscesses.
• In one Middle Eastern cohort of 67 liver abscess patients, 56 cases were pyogenic, and 91% occurred in males—highlighting both the predominance of PLA and male susceptibility in certain regions.

Demographic and Epidemiological Background

• Age: Risk increases with advancing age, particularly beyond 50 years.
• Sex: Male patients are at greater risk, with studies showing a relative risk of 2.6.
• Travel History: Important in suspected amoebic liver abscess; infection with Entamoeba histolytica is endemic in South and Central America, Africa, and Asia.
• Place of Origin or Immigration Status: Consider amoebic infection in immigrants from endemic areas.

Risk Factor Assessment

Underlying medical conditions

• Diabetes mellitus (odds ratio 3.6)
• Malignancy (particularly gastrointestinal)
• Cirrhosis (15-fold increased risk)
• Cardiopulmonary disease
• Immunosuppression (e.g. HIV/AIDS, chemotherapy, organ transplantation)

Medication and Procedure History

• Recent use of proton pump inhibitors
• Invasive hepatobiliary interventions (e.g. biliary stenting, sphincterotomy, TIPS, percutaneous tumour ablation)
• Recent chemotherapy or immunosuppressive therapy

Surgical or procedural history

• Recent abdominal trauma (blunt or penetrating)
• History of liver transplantation
• Recent dental infections or poor dentition (source of bacteraemia)

Presenting Symptoms

Constitutional symptoms

• Fever (continuous or spiking; occurs in >90%)
• Chills, night sweats
• Malaise, fatigue
• Unexplained weight loss

Gastrointestinal and abdominal complaints

• Right upper quadrant abdominal pain (50–75% of cases)
• Anorexia, nausea, vomiting
• Dark urine (may mimic viral hepatitis)

Respiratory symptoms

• Cough, dyspnoea, chest pain (may reflect diaphragmatic irritation or pleural involvement)
• Right shoulder pain (referred pain via phrenic nerve)

Pattern of Disease Onset

• Pyogenic liver abscess often has an insidious onset.
• Amoebic abscess tends to present more acutely.
• Solitary lesions may be associated with chronic constitutional symptoms, mimicking malignancy.
• Multiple abscesses are usually more acute and severe, often with systemic toxicity.

Specific Pathogen-Associated Features

• Klebsiella pneumoniae: May lead to metastatic complications (endophthalmitis, meningitis, brain abscess); systemic symptoms may persist even after drainage.
• Echinococcus granulosus (hydatid disease):
  • Often has an initial asymptomatic phase in childhood.
  • Symptomatic progression occurs over years as cysts enlarge (1–5 cm/year).
  • Liver involvement is common (≈66% of cases).
  • Symptoms arise from compression (e.g. biliary colic, obstructive jaundice, portal hypertension, Budd-Chiari syndrome) or rupture (peritonitis, anaphylaxis).

Rare or Context-Specific Clues

• Fever of unknown origin (FUO): Liver abscess may be an underlying diagnosis in indolent presentations.
• Anaemia and weight loss: Consider especially in solitary abscesses or elderly patients, where malignancy is a differential.
• History of bacteraemia, endocarditis, or intravascular infection may suggest haematogenous spread to the liver.
• Gastrointestinal inflammation (e.g. appendicitis, diverticulitis, pancreatitis): Can lead to portal vein pylephlebitis and seeding of the liver.

Common Examination Findings

Fever

• Present in up to 90% of cases.
  May be continuous or spiking.
• Often accompanied by chills and sweating.

Hepatomegaly

• Liver enlargement is a frequent finding and may be tender on palpation.
• A palpable liver edge or mass may be noted in the right upper quadrant (RUQ) or epigastrium, especially in abscesses involving the left hepatic lobe.

Abdominal Tenderness

• RUQ or midepigastric tenderness is common and correlates with hepatic involvement.
• More than 50% of patients exhibit abdominal tenderness on examination.
• Tenderness may be diffuse in cases of peritonitis or large abscess rupture.

Jaundice

• Occurs in up to 25% of patients, more frequently when:
  • Biliary tract obstruction is present
  • Multiple abscesses coexist
  • There is underlying cholangitis

Signs of Respiratory Involvement

• Decreased breath sounds in the right lower lung zone, possibly due to:
  • Atelectasis
  • Reactive pleural effusion
  • Diaphragmatic irritation
• Pleural or hepatic friction rubs may be heard if the Glisson capsule or diaphragm is inflamed.
• Some patients experience pleuritic pain or referred pain to the right shoulder.

Signs of Sepsis or Shock

• Tachycardia, hypotension, and clinical features of septic shock may be evident in severe cases.
• A small subset of patients, particularly those with ruptured hydatid cysts, may present with anaphylactic shock.

Uncommon or Specific Signs

• Ascites: Rare, but may occur with extensive peritoneal irritation or advanced disease.
• Charcot Triad (fever, RUQ pain, jaundice): Typically associated with cholangitis but may be seen in liver abscess as part of the differential diagnosis.
• Signs of extrahepatic complications:
  • In Klebsiella pneumoniae liver abscess, ocular (endophthalmitis), neurological (meningitis), and cerebral signs may follow systemic embolisation.
  • In Echinococcus granulosus (hydatid disease), compression signs develop as cysts enlarge (>10 cm), including:
    • Biliary colic, obstructive jaundice
    • Portal hypertension, Budd-Chiari syndrome
    • Bronchial fistula
    • Ruptured cysts may result in peritonitis or anaphylaxis.

Laboratory Investigations

Full Blood Count (FBC)

• Neutrophilic leukocytosis and anaemia of chronic disease.
• Suggests an infectious or inflammatory process but is non-specific.

Liver Function Tests (LFTs)

• Alkaline phosphatase: Elevated in approximately two-thirds of cases.
• Transaminases (ALT/AST) and bilirubin: Mildly elevated unless there is significant biliary involvement or advanced disease.
• Albumin: Often reduced (hypoalbuminaemia) in chronic or severe cases.

Coagulation Profile

• Prothrombin time (PT) and activated partial thromboplastin time (aPTT): Performed before any aspiration or intervention to rule out bleeding risk.
• Coagulopathy must be corrected before invasive procedures.

Blood Cultures

• Positive in ~50% of cases.
• Sensitivity decreases if antibiotics are administered prior to sampling.

C-Reactive Protein (CRP)

• Non-specific marker of inflammation.
• Can be used to monitor treatment response.

Serological and Stool Antigen Testing for Entamoeba histolytica

• Serum IgG antibody test: Positive in amoebiasis; remains positive for years.
• Stool ELISA or PCR: Useful in patients with diarrhoea.
• Antigen or DNA detection in aspirated pus: Diagnostic for amoebic liver abscess.
• Aspirate classically resembles "anchovy paste".

Imaging Studies

Contrast-Enhanced Computed Tomography (CT)

• Sensitivity: >95%.
• Well-defined, hypodense lesions with peripheral contrast enhancement.
• Gas within the lesion (seen in ~20%) suggests pyogenic infection.
• Identifies small (<1 cm) abscesses and evaluates for intra-abdominal spread or underlying malignancy.
• Guides percutaneous aspiration and drainage.

Ultrasonography (US)

• Sensitivity: 80–90%.
• Hypoechoic, irregularly bordered lesions.
• Internal septations or debris may be seen.
• Portable, no contrast needed, useful in critically ill patients.
• Allows real-time guidance for aspiration or catheter placement.
• Limitations: Operator-dependent and less sensitive for small lesions.

Radionuclide Scanning

• Includes technetium, gallium, and indium-labelled WBC scans.
• Sensitivity: indium (90%) > technetium (80%) > gallium (50–80%).
• Largely replaced by CT and US.

Chest Radiography (CXR)

• May show right-sided pleural effusion, elevation of the right hemidiaphragm, or basilar atelectasis.
• Typically supportive, used when respiratory symptoms are present.

Magnetic Resonance Imaging (MRI)

• More sensitive than CT for small abscesses.
• Low signal intensity on T1-weighted images.
• High signal intensity on T2-weighted images.
• Limited by cost and availability.
• Requires gadolinium contrast.

Microbiological and Percutaneous Diagnostic Procedures

Aspiration and Culture of Abscess Material

• Best obtained under CT or US guidance.
• Culture is positive in ~66% of cases.
• Direct aspiration yields better microbiological yield than fluid collected via drainage catheter.
• Contraindicated in coagulopathy or suspected hydatid cyst due to risk of anaphylaxis.

Percutaneous Drainage

• Standard of care for most pyogenic abscesses.
• Techniques include the Seldinger or trocar method under imaging guidance.
• Catheter should be flushed daily and removed when output is <10 mL/day or cavity collapse is seen.
• Preferred for abscesses >5 cm, multiloculated or ruptured lesions.
• Contraindicated in difficult access, peritonitis, uncorrected coagulopathy, viscous pus, or multiloculated abscesses.
• Failure to improve may require surgical drainage.

Hepatobiliary and Intra-abdominal Differentials

Acute Cholecystitis

• Presents with RUQ pain, fever, and leukocytosis.
• Murphy’s sign may be positive.
• Ultrasonography shows gallbladder wall thickening, stones, and pericholecystic fluid.
• No hepatic lesions on imaging.

Ascending Cholangitis

• Classically presents with Charcot's triad (fever, RUQ pain, jaundice); may progress to Reynolds’ pentad with hypotension and confusion.
• Ultrasound or MRCP/ERCP shows biliary dilation or obstruction.
• Biliary sepsis without hepatic parenchymal involvement distinguishes it from liver abscess.

Viral Hepatitis

• Presents with malaise, jaundice, and hepatomegaly.
• Fever may be present but is typically low-grade.
• Transaminases are markedly elevated; imaging shows diffusely hypoechoic or normal liver without focal lesions.

Drug-Induced or Autoimmune Hepatitis

• Can mimic acute hepatic inflammation.
• Pain is often absent, unlike the localised discomfort seen in liver abscess.
• Serological markers and drug history are key to diagnosis.

Hydatid Cyst (Echinococcus granulosus)

• Common in endemic regions.
• Presents with slowly enlarging RUQ mass, sometimes with compressive symptoms.
• Imaging shows well-defined cysts with daughter cysts or calcifications.
• Risk of anaphylaxis on rupture; aspiration contraindicated.

Cystadenoma or Cystadenocarcinoma

• Insidious onset of abdominal fullness or discomfort; fever and chills are absent.
• CT or ultrasound reveals complex cystic lesions with irregular walls and septations.
• Diagnosis confirmed via histopathology.

Inflammatory Pseudotumour

• Rare benign lesion, often in young men with prior infection or autoimmune conditions.
• Clinical features overlap with liver abscess, including fever and RUQ pain.
• Histological confirmation shows fibrous tissue with inflammatory cell infiltration.

Hepatocellular Carcinoma (HCC)

• May present with RUQ pain and hepatomegaly.
• Fever is typically absent.
• Imaging may reveal arterial enhancement with washout on venous phase.
• Confirmed by biopsy and tumour markers (e.g. AFP).

Secondary Liver Metastases

• Often asymptomatic or with systemic symptoms referable to the primary tumour.
• Fever uncommon, and laboratory markers less inflammatory.
• Requires full body imaging and biopsy for confirmation.

Thoracic and Other Differentials

Right Lower Lobe Pneumonia or Empyema Thoracis

• May present with pleuritic chest pain, cough, dyspnoea, and referred shoulder pain.
• Chest X-ray or CT thorax shows consolidation or pleural fluid.
• Diaphragmatic irritation may mimic hepatic pain.

Parapneumonic Pleural Effusion

• Presents similarly to pneumonia with dullness to percussion and decreased breath sounds at the lung base.
• May occur alongside or be mistaken for subphrenic or hepatic processes.

Appendicitis

• Particularly if retrocaecal or complicated, it may mimic RUQ pain.
• Differentiated by tenderness in the right lower quadrant, migration of pain, and classic gastrointestinal symptoms.

General Principles

• Prompt diagnosis and early empirical treatment are crucial.
• Most patients require a combination of antibiotics and drainage.
• The choice of antibiotics and method of drainage depends on clinical status, abscess size and complexity, and suspected pathogen.

Antibiotic Therapy

Empirical Therapy

• Empirical broad-spectrum coverage is started immediately in unstable patients.
• Targets gram-positive, gram-negative, and anaerobic organisms.
• Anaerobic coverage (e.g. metronidazole) should be continued throughout treatment.

Common Regimens

• Critically ill / ICU patients
  • Piperacillin/tazobactam
  • Imipenem/cilastatin or meropenem
  • Cefepime or levofloxacin plus metronidazole
  • Consider adding vancomycin if MRSA or resistant enterococci suspected
• Stable patients
  • Ceftriaxone or cefotaxime plus metronidazole
  • Ciprofloxacin, levofloxacin, or moxifloxacin plus metronidazole
  • Avoid fluoroquinolones where local resistance >10%

Special Considerations

• Fungal infection (e.g. Candida): Amphotericin B or fluconazole in immunocompromised patients
• Suspected ESBL-producing organisms: Use carbapenems
• Amoebic abscess:
  • Treated with metronidazole or tinidazole
  • Follow with luminal agents (e.g. paromomycin) to eradicate colonisation

Drainage Procedures

Indications

• Most abscesses >3 cm require drainage
• Urgent drainage if the patient is in shock or has multi-organ dysfunction

Techniques

Percutaneous Needle Aspiration

• For small or accessible lesions
• Provides material for culture

Percutaneous Catheter Drainage (Preferred for moderate/large abscesses)

• Preferred for >5 cm, multiloculated, or non-ruptured lesions
• Drain maintained until output <10 mL/day

Surgical Drainage

• Indicated if:
  • Percutaneous drainage fails
  • Abscess is ruptured or multiloculated
  • Patient has APACHE II score ≥15
  • Concomitant surgical pathology exists (e.g. diverticular abscess)
• Can be open or laparoscopic

Endoscopic Drainage

• ERCP with stenting in biliary-source abscesses
• Endoscopic ultrasound-guided drainage described in selected patients

Amoebic Abscess Drainage

• Usually not required unless:
  • Abscess is >5 cm or in the left lobe
  • No clinical response within 3–5 days
  • Diagnosis remains uncertain

Duration of Therapy

• Pyogenic abscess:
  • Typically 2–6 weeks (longer for multiple abscesses, K. pneumoniae, or poor drainage)
  • Begin with IV antibiotics, then transition to oral once clinically improving
  • Normalisation of CRP and resolution of fever guide therapy duration
• Amoebic abscess:
  • 7–10 days of nitroimidazole
  • Followed by a luminal agent to prevent recurrence

Follow-up and Long-Term Monitoring

• Serial imaging (CT or ultrasound) to confirm drainage and monitor response
• Persistent fever after 2 weeks may suggest inadequate drainage or superinfection
• Monitor for recurrence, especially in those with biliary pathology (25% recurrence rate)
• Nutritional support, medication toxicity monitoring, and renal function checks are essential
• Multidisciplinary approach:
  • Radiology for guided drainage
  • Surgery for failed drainage or ruptured abscesses
  • Gastroenterology for evaluation of underlying disease
  • Infectious diseases for complicated or resistant infections

Consultations

• Interventional radiology: Early involvement for diagnostic and therapeutic drainage
• General surgery: For failed percutaneous drainage or concurrent intra-abdominal pathology
• Gastroenterology: To assess for underlying gastrointestinal or biliary disease (colonoscopy, ERCP)
• Infectious diseases: For complex cases, fungal infections, or multidrug resistance

General

• Untreated liver abscess is universally fatal, due to risks of rupture, sepsis, and multiorgan failure.
• With timely treatment, mortality ranges between 2.5–30%, depending on the setting, population studied, and presence of complications.
• A large US population-based study reported an in-hospital mortality of 5.6%, which remained stable over a 10-year period despite rising incidence.

Factors Associated with Poor Prognosis

Host-related Factors

• Age >65 years: Associated with increased morbidity and mortality, though outcomes may be comparable to younger patients if aggressively managed.
• ICU admission or septic shock at presentation
• Comorbid conditions:
  • Cirrhosis
  • Chronic renal failure
  • Malignancy (hepatic or extrahepatic)
  • Diabetes mellitus
  • Alcoholism
• Immunocompromise: Particularly relevant in fungal liver abscess

Disease-specific Factors

• Multiple abscesses or multiloculated collections
• Biliary origin of the abscess
• Delayed diagnosis or treatment initiation
• Fungal infection
• Inadequate or delayed drainage
• Acute respiratory failure

Laboratory and Scoring Indicators

• APACHE II score ≥15 is strongly predictive of mortality
• Hypoalbuminaemia (<2 g/dL)
• Hyperbilirubinaemia (>3.5 mg/dL)
• Encephalopathy

Microbiological Features

• Infections with Klebsiella pneumoniae may be associated with a hypervirulent phenotype, especially in cryptogenic or metastatic cases.
• Fungal infections (e.g. Candida) are associated with higher mortality rates.

Prognosis in Specific Subtypes

Amoebic Liver Abscess

• Generally excellent prognosis with medical therapy alone.
• Risk factors for worse outcome include:
  • Bilirubin >3.5 mg/dL
  • Serum albumin <2 g/dL
  • Encephalopathy
  • Multiple abscesses

Hydatid Cyst (Echinococcal Abscess)

• Typically has a benign course.
• Around 57% remain stable, and 76% of untreated cases remain asymptomatic for years.
• Surgical intervention is required in approximately 15%, often delayed years after initial diagnosis.

Risk of Recurrence

• Recurrence is most common in patients with biliary tract abnormalities (≈25% recurrence rate).
• Underlying fistulous communications or incomplete source control should be investigated, typically via ERCP or MRCP.
• Cryptogenic liver abscess, particularly those caused by K. pneumoniae, has been associated with an increased risk of colorectal cancer, especially in East Asian populations—prompting some experts to recommend colonoscopy in selected patients.

Immediate and Short-Term Complications

Sepsis and Multiorgan Failure

• A common and serious complication contributing significantly to mortality.
• Requires broad-spectrum antimicrobial coverage and aggressive supportive care.
• Risk is increased in elderly, immunocompromised patients, or those with delayed treatment initiation.

Abscess Rupture

• Although rare, rupture can lead to pneumoperitoneum or generalised peritonitis.
• Emergent surgical intervention is typically required.

Subphrenic Abscess

• Occurs due to upward spread of infection beneath the diaphragm.
• Symptoms include referred right shoulder tip pain, cough, or hiccups due to diaphragmatic irritation.

Pleuropulmonary or Hepatobronchial Fistula

• Fistulisation into the bronchial tree presents with productive cough, often of foul or metallic-tasting sputum.
• Can also cause recurrent respiratory infections or empyema.

Hepatic Artery Pseudoaneurysm

• Results from erosion of the abscess into the hepatic arterial wall.
• Diagnosed via CT angiography.
• Requires urgent surgical or endovascular repair.

Abdominal or Hepatic Venous Thrombosis

• Can affect the portal vein, hepatic veins, or both.
• In one study, 42% of patients had venous thrombosis: 24% in portal veins, 22% in hepatic veins, and 4% in both.
• Best visualised using contrast-enhanced CT scans.
• May lead to complications such as portal hypertension or Budd-Chiari syndrome.

Liver Failure

• More frequent in those with pre-existing liver disease or large-volume abscesses.
• May accompany sepsis-induced multiorgan dysfunction.

Acute Pancreatitis

• A rare consequence; likely due to contiguous spread of inflammation.
• Presents with epigastric pain and vomiting, and confirmed by elevated pancreatic enzymes and imaging.

Metastatic Infectious Complications

• Especially common with hypervirulent Klebsiella pneumoniae infections.
• May cause:
  • Endophthalmitis
  • Central nervous system septic emboli
  • Septic pulmonary embolism
• Early recognition is critical as these may develop before or after liver abscess diagnosis.

Delayed or Variable-Onset Complications

Abscess Recurrence

• Common in patients with underlying biliary pathology (up to 25%).
• May indicate:
  • Incomplete source control
  • Presence of biliary-enteric fistula
• Requires repeat imaging and evaluation with ERCP or MRCP for definitive diagnosis and management.

Fistula Formation to Adjacent Organs

• Rare but serious; may involve:
  • Colon
  • Stomach
  • Small intestine
  • Kidneys
• Diagnosed with CT abdomen, with further confirmation by contrast studies or fistulography.

Preventive and Follow-up Measures

• Post-drainage antibiotic therapy for 4–6 weeks significantly reduces complication risk.
• Prophylactic antibiotics during procedures such as chemoembolisation or ERCP in high-risk patients may reduce future abscess formation.
• Close follow-up with imaging (typically CT or ultrasound) is necessary to confirm resolution.
• Persistent radiological abnormalities may linger even after clinical and laboratory resolution—imaging should be delayed unless new symptoms appear.
• Recurrent abscess warrants a thorough search for anatomical defects or unresolved infection source.

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