Medicq

Background
Bacterial abscess of the liver is relatively rare. It has been described since the time of Hippocrates (400 BC), with the first published review by Bright appearing in 1936. In 1938, Ochsner's classic review heralded surgical drainage as the definitive therapy; however, despite the more aggressive approach to treatment, the mortality rate remained at 60-80%.[1] (See images below.)[pic]Computed tomography (CT) scan findings of liver abscess are shown. A large, septated abscess of the right hepatic lobe is revealed. Abscess was successfully treated with percutaneous drainage and antimicrobial therapy. [pic]Computed tomography (CT) scan findings of liver abscess are shown. A large anterior abscess involving the left hepatic lobe is revealed. Abscess was successfully treatedwith percutaneous drainage and antimicrobial therapy.
The development of new radiologic techniques, the improvement in microbiologic identification, and the advancement of drainage techniques, as well as improved supportive care, have decreased mortality rates to 5-30%; yet, the prevalence of liver abscess has remained relatively unchanged. Untreated, this infection remains uniformly fatal.

The3 major forms of liver abscess, classified by etiology, are as follows:

• Pyogenic abscess, which is most often polymicrobial, accounts for 80% of hepatic abscess cases in the United States.
• Amebic abscess due to Entamoeba histolytica accounts for 10% of cases.
• Fungal abscess, most often due to Candida species, accounts for less than 10% of cases.
Next Section:Pathophysiology

Pathophysiology

The liver receives blood from both systemic and portal circulations. Increased susceptibility to infections would be expected given the increased exposure to bacteria. However, Kupffer cells lining the hepatic sinusoids clear bacteria so efficiently that infection rarely occurs. Multiple processes have been associated with the development of hepatic abscesses; theirrelative frequencies are listed in the image below.

[pic]
Table 4: Underlying etiology of 1086 cases of liver abscess compiled from the literature.
Appendicitis was traditionally the major cause of liver abscess. As diagnosis and treatment of this condition has advanced, its frequency as a cause for liver abscess has decreased to 10%.

Biliary tract disease is now the most common source ofpyogenic liver abscess (PLA). Obstruction of bile flow allows for bacterial proliferation. Biliary stone disease, obstructive malignancy affecting the biliary tree, stricture, and congenital diseases are common inciting conditions. With a biliary source, abscesses usually are multiple, unless they are associated with surgical interventions or indwelling biliary stents. In these instances, solitarylesions can be seen.

Infections in organs in the portal bed can result in a localized septic thrombophlebitis, which can lead to liver abscess. Septic emboli are released into the portal circulation, trapped by the hepatic sinusoids, and become the nidus for microabscess formation. These microabscesses initially are multiple but usually coalesce into a solitary lesion.

Microabscess formation canalso be due to hematogenous dissemination of organisms in association with systemic bacteremia, such as endocarditis and pyelonephritis. Cases also are reported in children with underlying defects in immunity, such as chronic granulomatous disease and leukemia.

Approximately 4% of liver abscesses result from fistula formation between local intra-abdominal infections.

Despite advances indiagnostic imaging, cryptogenic causes account for a significant proportion of cases; surgical exploration has impacted this minimally. These lesions usually are solitary in nature.

Penetrating hepatic trauma can inoculate organisms directly into the liver parenchyma, resulting in pyogenic liver abscess. Nonpenetrating trauma can also be the precursor to pyogenic liver abscess by causing...