Diagnostic Ultrasound - Abdomen and Pelvis

Amebic Hepatic Abscess
220
Diagnoses: Liver
PATHOLOGY
General Features
• Etiology
○ Entamoeba histolytica
○ Primary mode of infection: Human carriers pass amebic
cysts into stool
○ May become secondarily infected with pyogenic bacteria
• Associated abnormalities
○ Amebic colitis
• Disease pathway
○ Cystic form of Entamoeba histolytica gains access to body
via contaminated water
○ Mature cysts resistant to gastric acid, pass unchanged
into intestine
○ Cyst wall is digested by trypsin and invasive trophozoites
are released
○ Trophozoites enter mesenteric venules and lymphatics
○ Usually spread from colon to liver: Via portal vein (most
common) and lymphatics
○ Rarely direct spread
– Colonic wall to peritoneum
– Peritoneum to liver capsule and finally liver
Gross Pathologic & Surgical Features
• Usually solitary abscess
• Predominantly in right lobe
• Fluid dark, reddish-brown
• Consistency of anchovy paste or chocolate sauce
Microscopic Features
• Blood, destroyed hepatocytes
• Necrotic tissue and rarely trophozoites
○ Pleuropulmonary amebiasis (20-35%)
– Pulmonary consolidation or abscess
– Effusion, empyema, or hepatobronchial fistula
○ Peritoneal amebiasis (2-7.5%)
○ Pericardial or renal amebiasis
• Prognosis
○ Usually good after amebicidal therapy
○ Poor in individuals who develop complications
○ Mortality rate in USA: < 3%
– < 1% when confined to liver
– 6% with extension into chest
– 30% with extension into pericardium
Treatment
• 90% respond to antimicrobial therapy
○ Metronidazole or chloroquine
○ Iodoquinol for luminal treatment
• 10% require aspiration and drainage
DIAGNOSTIC CHECKLIST
Consider
• Rule out other liver pathologies, which may simulate
amebic abscess on imaging
○ Pyogenic or fungal abscess
○ Other cystic lesions
• Check for history of transplantation and ablation or
chemotherapy for liver tumor or metastasis, which may
simulate amebic abscess on imaging
Image Interpretation Pearls
• US: Solitary hypoechoic mass with internal low-level echo,
peripherally located
• CT: Unilocular, round or ovoid hypodense mass with rim or
capsule enhancement
• Diaphragmatic rupture in presence of adjacent hepatic
abscess suggests amebic cause
CLINICAL ISSUES
Presentation
• Most common signs/symptoms
○ RUQ pain, tender hepatomegaly
SELECTED REFERENCES
○ Diarrhea with mucus
• Clinical profile
○ Patient with history of diarrhea (mucus), RUQ pain, and
tender hepatomegaly
• Laboratory data
○ Stool exam: Usually nonspecific or negative
○ Indirect hemagglutination positive in 90% cases
Demographics
• Age
○ More common in 3rd-5th decades
○ Can occur in any age group
• Gender
○ M:F = 4:1
• Epidemiology
○ Approximately 10% of world's population is infected
withEntamoeba histolytica
○ Most common in India, Africa, Far East, Central and South
America
○ In United States: Recent travel to endemic area
Natural History & Prognosis
• Complications
http://radiologyebook.com/
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