SN5 SHORT NOTE 5M ★ High-yield

Differentiate amoebic from pyogenic liver abscess.

Pathology · 2nd Professional — Para-Clinical

Definition

A liver abscess is a localised collection of pus within the hepatic parenchyma. The two important types are amoebic and pyogenic.

Amoebic Liver Abscess

Caused by entamoeba histolytica, reaching the liver from colonic ulcers through the portal vein
The commonest extra-intestinal complication of amoebiasis, and common in India
Usually solitary and in the right lobe (about 80%), because the superior mesenteric vein carries blood preferentially there
Contents — thick, reddish-brown, odourless fluid, classically described as "anchovy sauce"; this is necrotic liver tissue, not pus, and contains few leucocytes
Trophozoites are found in the wall of the abscess, not in the centre, which is why aspirated fluid is usually sterile and amoeba-free — a point frequently examined
Aspirate is characteristically sterile on bacterial culture

Pyogenic Liver Abscess

Route	Source
Biliary (the commonest)	Ascending cholangitis from stones, stricture or tumour
Portal	Appendicitis, diverticulitis, inflammatory bowel disease — pylephlebitis
Arterial	Systemic bacteraemia, endocarditis
Direct extension	Cholecystitis, subphrenic abscess
Trauma	Penetrating or blunt injury

Usually multiple when biliary or haematogenous in origin
Organisms — E. Coli, Klebsiella, Streptococcus milleri, Bacteroides and other anaerobes; often mixed
Contents — frank, foul-smelling pus which grows organisms readily

Comparison

Feature	Amoebic	Pyogenic
Number	Usually solitary	Often multiple
Site	Right lobe, 80%	Either lobe
Age and sex	Young adult males; alcohol is a risk factor	Older; either sex
Contents	"anchovy sauce" — necrotic liver, odourless	Frank pus, foul-smelling
Culture of aspirate	Sterile	Organisms grown
Serology	Amoebic serology positive in over 90%	Negative
Jaundice	Uncommon	Common, especially with a biliary source
Treatment	Metronidazole alone in most cases, followed by a luminal amoebicide (diloxanide) to clear intestinal carriage	Antibiotics plus drainage, and treatment of the underlying source

CLINICAL PEARL

The amoebic abscess is not really an abscess, and that explains why it is treated with a drug rather than a drain. Its contents are liquefied liver tissue with few inflammatory cells, and the organisms sit in the wall. Metronidazole penetrates it and cures the great majority; aspiration is reserved for a large left lobe abscess threatening rupture into the pericardium, for failure to respond, or where the diagnosis is in doubt.

Clinical Features and Applied Aspects

Fever with rigors, right upper quadrant pain, tender hepatomegaly; the pain may be referred to the right shoulder tip through diaphragmatic irritation
Intercostal tenderness over the lower right ribs is a useful sign
Investigations — leucocytosis, raised alkaline phosphatase and ESR; ultrasound is the first-line imaging test; amoebic serology; blood cultures in pyogenic disease
Complications — rupture into the pleural cavity, lung (giving "anchovy sauce" sputum), peritoneum or pericardium; the last is the most dangerous and follows left lobe abscesses
Only 10 to 30% of patients with amoebic liver abscess have concurrent dysentery, so its absence does not exclude the diagnosis
In India, treat empirically for amoebiasis while investigating, since it is common, metronidazole is safe and cheap, and the response is rapid and itself diagnostic

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