Pyogenic hepatic abscesses are uncommon conditions that present diagnostic and therapeutic challenges to physicians. If left untreated, these lesions are invariably fatal.
Liver abscesses  have been recognized since the age of Hippocrates. In 1883, Koch described amebae as a cause of liver abscess. In 1938, Ochsner and Debakey published the largest series of pyogenic and amebic liver abscesses in the literature.  Since the late 20th century, percutaneous drainage has become a useful therapeutic option. [3, 4, 5, 6, 7]
Pyogenic bacteria can gain access to the liver through direct extension from contiguous organs or via the portal vein or hepatic artery. Hepatic clearance of bacteria via the portal system appears to be a normal phenomenon in healthy individuals; however, organism proliferation, tissue invasion, and abscess formation can occur with biliary obstruction, poor perfusion, or microembolization.
The organisms isolated most often are included below. Most abscesses contain more than one organism and frequently are of biliary or enteric origin. Blood culture results are positive in 33-65% of cases,  with positive results from abscess cultures reported in 73-100% of series. [8, 9] Escherichia coli is the most commonly isolated organism in Western series, whereas Klebsiella pneumoniae has emerged as a common isolate in patients with diabetes in Taiwan. [10, 11, 12, 13]
E coli - 33%
K pneumoniae - 18%
Bacteroides species - 24%
Streptococcal species - 37%
Microaerophilic streptococci - 12%
Biliary disease accounts for 21-30% of reported cases of pyogenic hepatic abscess. [4, 8, 14, 9] Extrahepatic biliary obstruction leading to ascending cholangitis and abscess formation is the most common cause [8, 9] and is usually associated with choledocholithiasis, benign and malignant tumors,  or postoperative strictures.
Biliary-enteric anastomoses (choledochoduodenostomy or choledochojejunostomy) have also been associated with a high incidence of liver abscesses. [3, 9] Biliary complications (eg, stricture, bile leak) after liver transplantation are also recognized causes of pyogenic liver abscesses.
Infection via portal system (portal pyemia)
The infectious process originates within the abdomen and reaches the liver via embolization or seeding of the portal vein. With the liberal use of antibiotics for intra-abdominal infections, portal pyemia is now a less frequent cause of pyogenic liver abscesses, but it still accounts for 20% of cases.  Appendicitis and pylephlebitis are the predominant causes. However, any source of intra-abdominal abscess, such as acute diverticulitis, inflammatory bowel disease, and perforated hollow viscus, can lead to portal pyemia and hepatic abscesses.
Hematogenous (via hepatic artery)
This infectious process results from seeding of bacteria into the liver in cases of systemic bacteremia from bacterial endocarditis or urinary sepsis or as a consequence of intravenous drug abuse. 
Blunt or penetrating trauma and liver necrosis from inadvertent vascular injury during laparoscopic cholecystectomy are recognized causes of liver abscess.  In addition, transarterial embolization and cryoablation of liver masses are now recognized as new etiologies of pyogenic abscesses. 
No cause is found in approximately half of the cases. However, the incidence is increased in patients with diabetes or metastatic cancer. Patients with repeated cryptogenic liver abscesses should undergo biliary and gastrointestinal evaluation. 
The incidence of pyogenic liver abscess has remained unchanged since just before the mid-20th century. In the United States, the incidence of pyogenic liver abscess is estimated to be 8-15 cases per 100,000 persons. This figure is considerably higher in countries where health care is not readily available. Studies indicate that the male-to-female ratio is approximately 2:1; the problem occurs most commonly in the fourth to sixth decade of life. 
When left untreated, pyogenic liver abscess is associated with a mortality of 100%. Early series reported mortalities higher than 80%. With early diagnosis, appropriate drainage, and long-term antibiotic therapy, the prognosis has improved markedly  ; mortality is now in the range of 15-20%. [9, 16] Poor prognostic factors are as follows:
Age older than 70 years
Lo et al performed a retrospective study of 741 patients with pyogenic hepatic abscesses with the aim of identifying risk factors associated with treatment failures.  Findings included the following:
The incidence of pyogenic hepatic abscess increased with increasing extended-spectrum beta-lactamase (ESBL) resistance
Elderly age (≥55 years), multiple abscesses, malignant etiology, and endoscopic intervention were independent predictors of failure of antibiotics-only therapy, whereas average duration of antibiotic therapy and average abscess size were not
Eastern Cooperative Oncology Group (ECOG) performance status of 2 or greater, preexisting hypertension, and hyperbilirubinemia were independent predictors of failure of percutaneous therapy, whereas multiple abscesses and average abscess size were not
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