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PH-GI31

Liver abscess

How bacteria reach the liver through the bile ducts, portal vein, hepatic artery or neighbouring tissue to form a pyogenic abscess, how Entamoeba dissolves liver into “anchovy paste”, and how a hydatid cyst differs from both.

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  • 5 steps · 9 questions
  • 3D normal anatomy

By the end, you can

  • Describe the routes by which infection reaches the liver and relate each to its usual sources and organisms.
  • Explain how a pyogenic liver abscess forms and causes fever, pain, referred shoulder pain and sepsis.
  • Explain how Entamoeba histolytica reaches and destroys the liver, and why its abscess holds “anchovy paste” rather than pus.
  • Compare a hydatid cyst with an abscess in its cause, wall, contents and dangers.
  • Recognise the gross and microscopic appearance and tests of each lesion, and explain how drainage, antibiotics, amoebicides and anti-parasitic treatment act on the mechanism.

What it is

A liver abscess is a cavity in the liver filled with pus or liquefied liver tissue. A pyogenic abscess is caused by bacteria, which reach the liver through the bile ducts, the portal vein, the hepatic artery or directly from nearby. An amoebic abscess is caused by the protozoan Entamoeba histolytica, carried from the colon in portal blood. The main look-alike is a hydatid cyst, the fluid-filled larva of the tapeworm Echinococcus, which is not an abscess unless it becomes infected.

3 types to tell apart
Pyogenic (bacterial) abscess
Pus from bacteria arriving by the biliary, portal, arterial or direct route, or with no source found; the commonest liver abscess in high-income countries.
Amoebic abscess
Liver destroyed by Entamoeba histolytica trophozoites, with sterile, reddish-brown contents; the commonest type where amoebiasis is endemic.
Hydatid cyst (the look-alike)
The slowly growing larval cyst of Echinococcus granulosus, with clear fluid and protoscolices; it can become infected and then behave like an abscess.

Normal function

Three ways in, and a filter that clears them

Every route into the liver from inside the body passes a . The brings blood from the gut, which normally carries a few bacteria and bacterial products absorbed through the bowel wall; the brings blood from the general circulation; and the carries bile away from the liver towards the duodenum.

The liver is a filter. , the macrophages lining the sinusoids and the largest fixed population of macrophages in the body, trap and kill the occasional bacteria arriving in portal blood. Bile flows steadily outwards and the sphincter of Oddi keeps duodenal contents out, so the bile ducts stay almost sterile.

An abscess forms when this clearance is overwhelmed: many organisms arrive at once, bile stagnates behind a blockage, or dead or poorly perfused liver gives bacteria somewhere to grow. How pus forms and is walled off in general is in the purulent inflammation lesson; this lesson follows what is particular to the liver.

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