Liver abscess

Pyogenic liver abscess is often a polymicrobial infection. The most commonly isolated organisms are Escherichia coli, Klebsiella species, Streptococcus constellatus, S anginosus, S intermedius (the 3 Streptococcus organisms are classified as the Streptococcus anginosis group), other streptococci species, Enterococcus, and anaerobes, including Bacteroides fragilis and Fusobacterium necrophorum.[4][6][8][14][15][16][17]Staphylococcus aureus and Pseudomonas species are less common causes of liver abscess. Recurrent pyogenic cholangitis (associated with hepatolithiasis) due to Salmonella typhi may cause pyogenic liver abscess. Abscesses caused by hypervirulent Klebsiella pneumoniae have been associated with extrahepatic complications, including endophthalmitis and central nervous system infections.[15][16] The incidence of Klebsiella liver abscess is increasing in North America.[16] In immunocompromised hosts, fungal abscess of the liver may occur. Amebic abscess may occur following infection with the parasite Entamoeba histolytica.[2] E histolytica (with possible amebic abscess development) is endemic in Central and South America, Africa, and Asia.[11] In the US, amebiasis is seen most commonly in immigrants and travelers from endemic areas.[2][12][13]

Liver abscesses form by spread of infection from one of the following sources:[8]

Biliary tree
Portal vein
Hepatic vein
Extension of contiguous infection
Penetrating trauma.

The biliary tract is the most common identifiable source of pyogenic liver abscess. Abscesses can also be formed by spread of infection along vascular routes.[18] Historically, pyogenic liver abscess was most commonly a complication of untreated or inadequately treated appendicitis; diverticulitis is another mechanism that can lead to portal pyemia and pyogenic liver abscess.[19] The portal vein drains the gastrointestinal tract, gallbladder, and pancreas. Pylephlebitis (portal vein inflammation) from inflammatory bowel disease, pancreatitis, appendicitis, or diverticulitis can result in liver abscess. A migrated foreign body can also be associated with liver abscess.[20] Other underlying conditions associated with an increased risk of liver abscess are:

Diabetes mellitus[21]
Cancer (either primary hepatocellular cancer or extrahepatic primary cancer)
Cirrhosis[22]
Prior liver transplant[3]
Cardiopulmonary disease[14]
Immunocompromise.[2]

Liver abscess may occur following chemoembolization or percutaneous ablation of hepatic neoplasms, endoscopic biliary sphincterotomy, hepatic cryotherapy, or other instrumentation of the hepatobiliary system.[23] In approximately 40% of cases, no specific cause of liver abscess is identified.[19] Such cases may result from bacteremia in patients with poor dentition. Bacteremia, endocarditis, or other intravascular infections are infrequently complicated by liver abscess.

Traditional classification of liver abscess

Pyogenic

Typically referring to bacterial causes
Complicating fungal infection may occur in people with immunosuppression.

Amebic

Caused by infection with the parasite Entamoeba histolytica
Patients originate from or have visited endemic areas.[2]

Pathophysiology

Classification

Traditional classification of liver abscess