Definition/General
Introduction:
Liver abscess is a localized collection of pus within liver parenchyma
FNAC is both diagnostic and therapeutic
Shows acute inflammatory cells with necrotic debris
Common types include pyogenic and amoebic abscesses.
Origin:
Results from bacterial, parasitic, or fungal infections
Pyogenic abscess: ascending cholangitis, portal seeding
Amoebic abscess: Entamoeba histolytica infection
Fungal abscess: immunocompromised patients
Hydatid cyst: Echinococcus infection
Direct extension from adjacent organs.
Classification:
Etiology-based: Pyogenic abscess (bacterial)
Amoebic abscess (E
histolytica)
Fungal abscess (Candida, Aspergillus)
Hydatid cyst (Echinococcus)
Location: right lobe more common
Size: small (<5 cm) vs large (>5 cm)
Number: solitary vs multiple.
Epidemiology:
More common in developing countries
Pyogenic abscess: elderly patients, biliary disease
Amoebic abscess: young males, endemic areas
Peak incidence: 4th-6th decades
Male predominance in amoebic abscess
Indian subcontinent: high prevalence of amoebic liver abscess.
Clinical Features
Presentation:
Fever with chills (most common)
Right upper quadrant pain
Hepatomegaly with tender liver
Jaundice (if biliary obstruction)
Weight loss and malaise
Shoulder pain (diaphragmatic irritation)
Pleuritic chest pain (right-sided).
Symptoms:
High-grade fever with rigors
Severe abdominal pain (right hypochondrium)
Nausea and vomiting
Diarrhea (amoebic cases)
Dyspnea (large abscess)
Night sweats
Anorexia and weight loss
Productive cough (if rupture into lung).
Risk Factors:
Biliary tract disease (cholangitis, cholelithiasis)
Portal pyemia (appendicitis, diverticulitis)
Immunocompromised state (diabetes, HIV)
Travel to endemic areas (amoebic)
Poor sanitation
Alcohol abuse
Previous hepatic intervention
Inflammatory bowel disease.
Screening:
Complete blood count: leukocytosis with left shift
Liver function tests: elevated enzymes
Inflammatory markers: elevated ESR, CRP
Blood cultures
Amoebic serology
Imaging: ultrasound, CT, MRI
Aspiration for diagnosis and culture.
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Gross Description
Appearance:
FNAC yields purulent material
Thick, viscous pus
Yellow-green (pyogenic) or chocolate-brown (amoebic)
Foul-smelling (anaerobic bacteria)
Blood-tinged in some cases
Necrotic debris abundant
May contain parasitic elements.
Characteristics:
Purulent aspirate with inflammatory cells
Neutrophilic predominance (acute cases)
Macrophages with debris
Bacterial colonies may be visible
Amoebic trophozoites (amoebic abscess)
Fungal elements in immunocompromised
Eosinophils (hydatid cyst).
Size Location:
Variable size: few cm to >20 cm
Right lobe predominance (75-80%)
Posterior segments more common
Single cavity (amoebic) vs multiple cavities (pyogenic)
Wall thickness variable
Satellite lesions may be present.
Multifocality:
Solitary abscess more common (70%)
Multiple abscesses (30%): suggests hematogenous spread
Bilateral involvement possible
Extrahepatic extension: diaphragm, lung, peritoneum
Secondary infection of pre-existing lesions
Rupture complications: peritonitis, empyema.
Microscopic Description
Histological Features:
Acute inflammatory infiltrate: neutrophils predominant
Necrotic hepatocytes
Fibrinous exudate
Macrophages with debris
Bacterial colonies (pyogenic)
Amoebic trophozoites (12-40 μm)
Abscess wall: granulation tissue, fibrosis.
Cellular Characteristics:
Neutrophils: mature forms with nuclear lobes
Macrophages: activated with abundant cytoplasm
Lymphocytes and plasma cells (chronic)
Amoebic trophozoites: large, motile, karyosome
Bacterial forms: cocci, rods, filamentous
Fungal hyphae or yeasts.
Architectural Patterns:
Central necrosis with liquefaction
Inflammatory cell infiltration
Abscess wall formation
Granulation tissue
Fibroblastic proliferation
Vascular proliferation
Chronic changes: fibrosis, calcification.
Grading Criteria:
No standard grading system
Assessment based on inflammatory activity
Acute vs chronic changes
Organism identification
Wall formation degree
Necrosis extent
Surrounding parenchyma changes.
Immunohistochemistry
Positive Markers:
CD68 (macrophages)
Myeloperoxidase (neutrophils)
CD3 (T-lymphocytes)
CD20 (B-lymphocytes)
Smooth muscle actin (myofibroblasts)
CD31 (endothelial cells)
Bacterial/fungal stains (organism identification).
Negative Markers:
Cytokeratins (negative, excludes carcinoma)
Hepatocyte marker (absent in necrotic areas)
AFP (negative)
CD34 (lost in inflammatory areas)
Specific organism stains (to exclude other pathogens).
Diagnostic Utility:
Limited utility in FNAC diagnosis
Organism identification using special stains
PAS stain: fungal elements
GMS stain: fungal walls
Gram stain: bacterial morphology
Trichrome: amoebic trophozoites
Exclude malignancy.
Molecular Subtypes:
Bacterial identification: 16S rRNA sequencing
Amoebic diagnosis: PCR, antigen detection
Fungal identification: DNA sequencing
Antimicrobial resistance patterns
Virulence factors
Epidemiologic typing.
Molecular/Genetic
Genetic Mutations:
Host susceptibility genes: immune response
Pathogen virulence genes
Antibiotic resistance genes
Inflammatory response genes: cytokine production
Complement system genes
HLA associations with susceptibility.
Molecular Markers:
Inflammatory cytokines: IL-1β, TNF-α, IL-6
Chemokines: IL-8, MCP-1
Acute phase proteins: CRP, SAA
Pathogen-specific antigens
Complement activation markers
Tissue damage markers.
Prognostic Significance:
Organism type: bacterial vs parasitic
Abscess size: larger worse prognosis
Multiple abscesses: complicated course
Immune status: immunocompromised poor outcome
Timely diagnosis: better prognosis
Complications: rupture, sepsis.
Therapeutic Targets:
Antimicrobial therapy: organism-specific
Percutaneous drainage
Anti-inflammatory agents
Supportive care: fluid, nutrition
Surgical drainage (large/complicated)
Treatment duration: 4-6 weeks minimum.
Differential Diagnosis
Similar Entities:
Pyogenic vs amoebic abscess
Necrotizing hepatocellular carcinoma
Infected hepatic cyst
Cholangiocarcinoma with necrosis
Metastases with necrosis
Hydatid cyst
Hematoma with secondary infection.
Distinguishing Features:
Pyogenic abscess: bacteria on stain, neutrophils, gas formation
Amoebic abscess: trophozoites, chocolate pus, young males
HCC: malignant cells, AFP elevation
Infected cyst: epithelial lining
Hydatid: protoscolices, laminated membrane.
Diagnostic Challenges:
Sterile abscess (prior antibiotic therapy)
Amoebic trophozoites identification
Mixed infections
Malignancy with secondary infection
Chronic abscess vs neoplasm
Atypical presentations in immunocompromised.
Rare Variants:
Tuberculous abscess
Actinomycotic abscess
Cryptococcal abscess
Nocardia abscess
Mixed bacterial-parasitic
Gas-forming abscess
Chronic granulomatous abscess.
Sample Pathology Report
Template Format
Sample Pathology Report
Complete Report: This is an example of how the final pathology report should be structured for this condition.
Clinical Information
Patient with [clinical presentation], imaging shows [liver lesion characteristics]
Specimen Description
Aspirated [volume] ml of [pus characteristics]
Cytomorphological Features
Shows [inflammatory cells] with [necrotic debris, organisms]
Organism Identification
Shows [bacteria/amoebic trophozoites/fungal elements/no organisms seen]
Special Stains
Gram stain: [results]
PAS/GMS: [results]
Trichrome: [results for amoeba]
Differential Diagnosis
Differential includes [pyogenic vs amoebic vs fungal abscess]
Final Cytological Diagnosis
Liver abscess, [type if determinable]
Recommendations
Recommend [culture, antimicrobial therapy, drainage, follow-up]