Infection of the bile ducts (cholangitis) is nowadays the most common underlying cause of liver abscess, especially among the elderly. Prior to advances in management and treatment, complicated appendicitis and infections within the abdomen were the most common causative conditions. When evaluating patients with liver abscesses, it is important to assess any past occurrence of predisposing diseases and conditions.

Specific signs and symptoms for liver abscess range widely and include fever, chills, decreased appetite, fatigue, nausea, jaundice, cough or hiccups because of involvement of the diaphragm, right upper quadrant tenderness and pain with possible extension in the left upper quadrant or the right shoulder and an enlarged, palpable liver [9]. Abdominal pain may not be present in all cases.

Liver abscesses that occur beneath the diaphragm can reach the thorax and result in the formation of a lung abscess or empyema. Such a process, nonetheless, takes place very rarely. Other complications that are associated with liver abscesses include peritonitis or even frank sepsis.

Workup in patients with a liver abscess is broad and initially includes a complete blood count (CBC), blood cultures, PT and aPTT, and an assessment of the serum levels of aminotransferase, alkaline phosphatase, bilirubin and albumin.

Patients usually exhibit anemia and high neutrophil counts, in addition to abnormal liver function tests such as alkaline phosphatase. These findings, nonetheless, are non-specific and are not sufficient for diagnosis. Because the disease commonly requires intervention for diagnostic and treatment purposes, evaluating PT and aPTT is important to rule out any coagulopathy or a tendency for excessive bleeding. C-reactive protein levels should also be assessed to detect any inflammatory process and may occasionally help to monitor treatment response [10]. The organism responsible for the formation of the abscess can be identified in up to 50% of patients after culturing blood samples.

On the other hand, amebiasis is diagnosed with serologic evaluation of E. hystolitica infection. The Entamoeba histolytica enzyme immunoassay (EIA) can only be used if there is concomitant diarrhea, and may detect the bacterial antigen in a stool sample.

Imaging is of critical importance for diagnosis. The modalities of choice are abdominal CT scanning with contrast enhancement or an abdominal ultrasound [11]. Nonetheless, because of higher sensitivity and its capacity to clearly visualize organs other than the liver, CT scanning is usually preferred. Ultrasound still possesses distinctive advantages that may be especially beneficial in particular cases. It has generally lower costs, is widely available and does not necessitate the administration of a contrast agent. Some cases require the use of both modalities, particularly when high suspicion is maintained in the context of negative ultrasound findings. Both imaging tests will show a liver abscess as a fluid collection with associated edema, typically on the right side.

After imaging is performed, aspiration of the abscess is usually necessary. It allows for the establishment of a definitive diagnosis and can help in choosing an appropriate antibiotic. Fluid collected from the aspiration can subsequently be sent for Gram staining and culturing in aerobic and anaerobic environments. It is important to mention that fluid collected via a drain cannot be used to uncover the causative organism.

The typical consistency of the aspirate is that of an "anchovy paste" or a "chocolate sauce". It is a thick fluid with a red to brownish color [12]. The polymerase chain reaction test or detection of specific antigens can conclusively establish the diagnosis as well as the organism responsible for the development of the disease.

Aspiration is not recommended in all cases. It should be avoided whenever a coagulopathy is suspected in light of abnormal PT and aPTT results. In addition, it should not be performed in cases of hydatid cysts, as cyst puncture is associated with a potential risk of anaphylaxis and death. Nonetheless, when amebic abscess is still suspected or the aspiration is therapeutic, patients with hydatid cysts may undergo the procedure.

Finally, any pulmonary symptoms or findings on the physical exam should prompt the performance of a chest x-ray to rule out pleural effusions, abscesses or empyema.

The cornerstone of treatment for hepatic abscesses is surgical or percutaneous drainage. Treatment with antibiotics is generally complementary but is very rarely sufficient on its own [13]. Severe and serious complications can result from liver abscesses that are not treated, such as sepsis, empyema or peritonitis. They are generally caused by a rupture of the abscess into the adjacent spaces in the peritoneum, thorax and retroperitoneum.

Drainage of a liver abscess can be performed surgically or percutaneously. Surgical treatment is nowadays recommended only under very specific conditions that include the presence of signs of peritonitis or abdominal pathology that necessitate surgical intervention such as diverticular disease, recurrent failure of drainage procedures and the presence of a complicated abscess with multiloculation, thick pus and a thick wall. Surgery is completely contraindicated in cases of multiple organ failure associated with shock.

Open surgery can be approached along two manners, transperitoneally or transpleurally. In the transperitoneal approach, an exploration of the abdomen is possible, allowing the clear visualization of nearby organs and structures and the detection of other abscesses and possible underlying causes of the abscess. The transpleural approach, on the other hand, allows for easier access into the abscess but does not make it possible to identify other lesions or the presence of an underlying abdominal disease process.

Prognosis varies and depends on various factors. These include the overall size of the liver abscess, the organism responsible for the infection and the comorbidities that the patient suffers from [8].

Liver abscesses are generally associated with infections by multiple microbes. The two most common organisms are Escherichia coli and Klebsiella pneumoniae. The latter seems to be increasingly involved in the condition and is particularly prominent in cases of endophthalmitis [3]. On the other hand, enterobacteriaceae are more common when the infection targets the biliary system.

Anaerobic bacteria play a very important role in the etiologic process leading to the disease. They came to prominence in 1974 when it was discovered that they are involved in 45% of all cases of pyogenic liver abscesses. Improvements in culturing methodologies have likely contributed to an increase in the frequency of studies reporting their presence. The most common anaerobic bacteria that are associated with liver abscesses include the Fusobacterium and Bacteroides species, in addition to microaerophilic and anaerobic streptococci. The most frequent source of infection is the colon.

Abscesses that involve Staphylococcus aureus result from dissemination through the blood stream from distant locations. This may be a common occurrence in endocarditis. On the other hand, S. milleri is associated in liver abscesses that develop in patients suffering from Crohn disease and can be present in monomicrobial or polymicrobial infections.

E. histolytica is the most common cause of amebic liver abscess. Normally, E. histolytica infects the bowel but can reach the liver through extraintestinal spread. Individuals at risk for fungal abscesses with Candida albicans are usually immunodeficient due malignancies, organ transplantation or other acquired or genetic causes. Furthermore, an extended exposure to antibiotics disrupts the normal flora in the gastrointestinal system and may lead to fungal colonization with Candida albicans. Organisms that have been also associated with liver abscesses are Eikenella corrodens, Brucella melitensis, Yersinia enterocolitica, Salmonella typhi and the Actinomyces species.

Finally, hepatocellular carcinoma may increase the risk of pyogenic liver abscess formation. Physicians should suspect a malignant cause of pyogenic liver abscesses in regions with high prevalence of hepatocellular carcinoma (HC) and in patients who are at risk for HC [4].

The incidence of liver abscess is 3.6 cases for every 100,000 individuals in the United States and Britain [5]. This makes liver abscess a rare disease. Incidence is more elevated in many regions of Asia. Studies report that it may reach to up 15 cases for every 100,000 a year in Taiwan.

Amebic abscesses, on the other hand, occur most commonly in Asia, Africa, South and Central America. Amebiasis is rare in the developed world and is usually found among immigrants or travelers that were previously present in countries with high prevalence.

The incidence of liver abscess has been increasing, although associated fatalities are stable or even decreasing. The disease seems to increase with age and has a predilection for men over women [6]. Nonetheless, it is important to point out that increases in incidence can be attributed to improvements in diagnostic strategies as well.

The liver is very susceptible to infection, given its extensive blood supply through the portal and systemic circulation. The most common cause of liver abscess is nowadays biliary tract disease, although previously, appendicitis was the main culprit [7]. When the biliary tract is involved, many abscesses tend to be present, except for cases when the infection is related to surgical intervention or the insertion of biliary stents. Usually, the right lobe of the liver is much more affected than the left lobe. It is thought that the different systems of blood circulations underlie the higher predilection for the right lobe. In addition, the right lobe contains a more extensive biliary network and generally more hepatic tissue.

The development of liver abscesses can be prevented by prompt diagnosis and treatment of infections that can occur within the abdomen. Primary preventive measures may include treatment with antibiotics or ERCP (endoscopic retrograde cholangiography).

A liver abscess implies the presence of localized necrotic tissue within the liver, combined with inflammatory processes. It is usually caused by infection with a number of microorganisms, that can be bacteria, parasites or fungi [1]. Most commonly, the infection is polymicrobial, although sometimes a single microorganism can be involved. The most frequently involved agents are Escherichia coli and Klebsiella pneumoniae. Staphylococcus aureus may be detected in cases of widespread hematogenous spread of bacteria, such as in endocarditis. The incidence of liver abscess remains low in the developed world but is much more elevated in regions of Asia, Africa, South and Central America [2]. A liver abscess can also be caused by amebiasis, a parasitic disease resulting from infection with Entameba histolytica. A hepatic abscess is nowadays most commonly caused by complications of infections of the biliary tree while, previously, appendicitis used to be the most prominent underlying factor. Patients can present with a range of symptoms that include right upper quadrant pain and tenderness, nausea, fatigue, fever and jaundice. Treatment consists of surgical or percutaneous drainage in combination with the administration of antibiotics. Prognosis is variable and depends on the underlying cause.

A liver abscess occurs when there is a localized infection in the liver that manifests with a collection of dead tissue and inflammatory cells. Infection with several microorganisms can lead to the development of liver abscesses, such as bacteria, fungi or parasites. Nowadays, the condition most commonly develops due to complications of an infection of the bile draining tubes (biliary tree). Appendicitis used to be the most common cause that lead to the development of liver abscesses. Patients usually present with pain on the right upper side of the abdomen, fatigue, fever and sometimes jaundice. Diagnosis is established after the performance of several blood and imaging tests to visualize the abdomen. A liver abscess is treated with antibiotics in combination with the performance of procedures that directly drain the abscess and eliminate it. Outcomes vary greatly depending on the underlying cause and the microorganism involved.

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