Pyogenic abscesses in the liver occur secondary to other sources of bacterial sepsis. Up to 60% of cases arise from direct spread of bacteria from biliary infections such as empyema of the gallbladder or cholangitis. Ruptured appendicitis or diverticulitis are other potential sources for bacterial seeding to the liver.
For liver abscesses arising from an intra-abdominal infection, it is important to note that hematogenous seeding is not the usual pathway for the development of the abscess; rather, the mechanism of spread of infection to the liver is along channels within the peritoneal cavity. For unknown reasons, liver abscesses are usually found in the right lobe of the liver.
Microbiology. The bacteria cultured from pyogenic liver abscesses reflect the origin of the infectious process. Most commonly, mixed species are isolated, with one third of cultures containing anaerobes. When the biliary tree is the source, enteric Gram-negative bacilli and enterococci are common isolates. When the abscess develops from hematogenous seeding, there is most likely a single organism responsible, such as Staphylococcus aureus or Streptococcus milleri. Fungal abscesses have been associated with patients who are recovering from chemotherapy. There should be suspicion of amebic abscesses in patients who are from or have recently traveled to an endemic area in the last 6 months.
Fever and abdominal pain are the most common symptoms, whereas nonspecific symptoms such as anorexia, weight loss, chills, and malaise may also be present.
Laboratory findings are usually nonspecific, such as leukocytosis and elevated serum alkaline phosphatase. A chest x-ray may demonstrate new elevation of the right hemidiaphragm, an infiltrate at the right lung base, or a right-sided pleural effusion. Definitive diagnosis is by CT scanning.
Treatment consists in identifying the infectious source as well as managing the liver abscess. Pyogenic liver abscesses require drainage and systemic antibiotic therapy. Drainage can be performed percutaneously in most cases, but an operative procedure is recommended when there are multiple, large, loculated abscesses and in patients who otherwise require laparotomy for the underlying cause of the abscess. Drains are usually left in place until drainage becomes minimal, typically 7 days. Empirical antibiotic treatment should include coverage for bowel flora (e.g., metronidazole plus ciprofloxacin or monotherapy with piperacillin/tazobactam). Once identification has been made of the causative organism(s), antibiotic therapy should be modified to reflect their sensitivities. Aggressiveantibiotic therapy should continue for at least 1 week beyond clinical recovery and resolution of the abscess on follow-up imaging.