Pyogeinic liver abscess is caused by the local inflammatory reaction caused by bacteria in hepatic parenchyma leading to the development of intrahepatic pus collection.^[1][2]They account for 80% of liver abscesses in developed world.^[3]

Hippocrates described pyogenic liver abscess based on the type of fluid recovered from abscess. In 1938, Ocshner and colleagues reported that the major causal factors leading to hepatic abscess were appendicitis and amoebiasis.^[4]

Pyogenic liver abscess may be classified according to international classification of diseases-10 (ICD-10) into K75.0.^[5].

Development of pyogenic liver abscess is the result of infection through the following routes like portal vein (also from pylephlebitis of portal vein), hepatic arteries as metastatic abscesses, direct spread from nearby infection, trauma and retroperitoneal extension from appendix.^[6][4][7][8]Ascending biliary infection is the most common source of pyogenic liver abscess.

Common causes of pyogenic liver abscess include hepatobiliary, portal, arterial, traumatic and cryptogenic causes.

Pyogenic liver abscess must be differentiated from other diseases with similar presentation such as amoebic liver abscess, fungal liver abscess, echinococcal (hydatid) cyst and malignancy (hepatocelluar carcinoma or metastasis).^{[9][10][11][12]}

Common risk factors in the development of pyogenic liver abscess are immunodeficiency, diabetes mellitus, pancreatic or hepatobiliary disease and liver transplant.^{[4][13][14][15]}

According to the U.S. Preventive Service Task Force (USPSTF), there is insufficient evidence to recommend routine screening for pyogenic liver abscess.

If left untreated, pyogenic liver abscess may progress to peritonitis or pleuritis secondary to rupture of the abscess into peritoneal or pleural cavities and sepsis.^[16][17][18]Complications of pyogenic liver abscess include septicemia, intraabdominal abscess, hepatic failure, renal failure, recurrent liver abscess and free peritonitis.^[19]The prognosis of liver abscess depends on underlying risk factors such as advanced age, malignancy, jaundice, multiple abscesses, heamoglobin <10g/dl and elevated blood urea nitrogen.^[4]

Symptoms of pyogenic liver abscess include abdominal pain, right lower chest pain, fever, chills, night sweats, nausea, vomiting, loss of appetite, right shoulder pain, weight loss, diarrhea, dyspnea and yellowish discoloration of skin (jaundice).^[5][20]

Common physical examination findings associated with pyogenic liver abscess include high grade fever, yellowish discoloration of skin (jaundice), icteric sclera, reduced breath sounds or crepitations at the base of lung, hepatomegaly with point tenderness, and abdominal guarding or rebound tenderness on palpation, dullness on percussion, and absent bowel sounds.^[21]

Laboratory tests consistent with diagnosis of pyogenic liver abscess include complete blood picture, ESR, C-reactive protein, liver function tests, pus culture, and blood culture.^[7]

There are no ECG findings associated with pyogenic liver abscess.

Chest X ray findings include atelectasis, pulmonary infiltrates, pleural effusion, elevated right hemidiaphragm, and gas within the abscess or biliary tree or beneath the diaphragm.^[5]

CT scan findings of pyogenic liver abscess include peripherally enhancing and centrally hypo attenuating lesions, solid or gas in the lesions (gas in the form of bubbles or air fluid levels), segmental, wedge-shaped or circumferential perfusion abnormalities, early enhancement may be seen on contrast enhanced CT scans, the double target sign and cluster sign.^{[22][23][24][25]}

MRI findings of pyogenic liver abscess include hypointense and heterogenous centrally on T1, hyperintense signal on T2, enhancement of the capsule and multiple septations on T1+C, high signal within the abscess cavity on DWI, and low signal within the abscess on ACD.^[26][5][27]

The ultrasound findings include round or oval shape, hypoechoic appearance with fine and homogeneous echoes, gas bubbles within the abscess, and absence of central perfusion on color doppler.^[28][29][30]

Other diagnostic studies include radionucleide scans which use technetium, indium, or gallium. They detect lesions <2 cm in size. These scans cannot distinguish between the cyst, tumor, or abscess and need confirmation with other diagnostic tests.^[31]

Treatment of pyogenic liver abscess include non-surgical treatment and open surgical drainage. Non-surgical treatment treatment includes conservative management with antibiotics alone and percutaneous drainage.^[19]

The maninstay of treatment of pyogenic liver abscess is percutaneous darinage of abscess. Other methods used are open surgical drainage and endoscopic retrograde cholangiopancreatography(ERCP).^{[32][33][2][34][8]}

The risk of developing pyogenic liver abscess can be reduced by prompt treatment of abdominal and other infections.^[5]

Secondary prevention strategies following pyogenic liver abscess include long term monitoring which helps in preventing the complications and recurrence , monitoring the abscess cavity weekly for adequate drainage using CT or USG, persistent fever more than 2 weeks of therapy is an indication for more aggressive drainage, prolonged antibiotic therapy after discharge of patient is recommended and presence of underlying liver disease is the predisposing factor for the recurrence of pyogenic liver disease.^[35]

Hippocrates described pyogenic liver abscess based on the type of fluid recovered from abscess. In 1938, Ocshner and colleagues reported that the major causal factors leading to hepatic abscess were appendicitis and amoebiasis.^[1]

• Hippocrates described pyogenic liver abscess based on the type of fluid recovered from abscess.
• In 1938, Ocshner and colleagues reported that the major causal factors leading to hepatic abscess were appendicitis and amoebiasis.^[1]
• Historically, the recommended treatment for liver abscess is open surgical drainage.
• In 1953, McFadzean and associates in Hong Kong suggested closed aspiration and antibiotic drugs for treatment of solitary pyogenic liver abscess.^[2]

Pyogenic liver abscess may be classified according to international classification of diseases-10 (ICD-10) into K75.0.^[1].

• Pyogenic liver abscess may be classified according to international classification of diseases-10 (ICD-10) into:^[1]

• K75.0

• Classification based on source of infection:^[2]

Development of pyogenic liver abscess is the result of infection through the following routes like portal vein (also from pylephlebitis of portal vein), hepatic arteries as metastatic abscesses, direct spread from nearby infection, trauma and retroperitoneal extension from appendix.^[1][2][3][4]Ascending biliary infection is the most common source of pyogenic liver abscess.

• Development of pyogenic liver abscess is the result of extension of infection through the following:^[1][2][3][4]

• Portal vein (also from pylephlebitis of portal vein)
• Hepatic arteries as metastatic abscesses
• Direct spread from nearby infection
• Trauma
• Retroperitoneal extension from appendix (suppurative appendicitis most frequent source of infection)

• Ascending biliary infection is the most common source of pyogenic liver abscess.
• Right lobe of liver is most commonly involved due to its greater blood supply than caudate and left lobes.
• Bacteria involved in pyogenic liver abscess include:

• In healthy patients the reticuloendothelial cells (kupffer cells) of liver control the transient portal bacteremia but in elderly and immunocompromised the bacteria can overwhelm the kupffer cells and lead to an abscess.^[5]

• Single or multiple cavities, filled with fowl smelling, creamy yellow necrotic material, usually in right lobe of liver.
• The abscess may have fibrous capsule which is a centimeter or more thick and gradually merges into the liver parenchyma.

• Multiple neutrophilic abscesses with areas of necrosis are seen in the liver parencyma.^[6][7]
• Suppuration, liquefaction with presence of fibrino-purulent debris, and fibrosis are seen depending on stage.
• The edges of the cavities are composed of a chronic inflammatory infiltrate consisting of lymphocytes, epithelioid macrophages, eosinophils, and neutrophils.
• Adjacent hepatocytes appear reactive.

• Common causes of pyogenic liver abscess include hepatobiliary, portal, arterial, traumatic and cryptogenic causes.^[1]

• The causative organisms of pyogenic liver abscess include:

Pyogenic liver abscess must be differentiated from other diseases with similar presentation such as amoebic liver abscess, fungal liver abscess, echinococcal (hydatid) cyst and malignancy (Hepatocellular carcinoma or metastasis).^[1][2][3][4]

Pyogenic liver abscess must be differentiated from:^{[1][2][3][4][5][6][7][8][9][10]}

Pyogenic liver abscess accounts for 48% of all visceral abscesses and 13% of intra-abdominal abscesses.^[1]

• Pyogenic liver abscess accounts for 48% of all visceral abscesses and 13% of intra-abdominal abscesses.^[1]
• The annual incidence is 2.3 cases per 100,000.^[2]
• The incidence of pyogenic liver abscess in developed countries is 0.5% – 0.8% and frequency of admissions to hospital is 20 per 100,000.^[3]

Pyogenic liver abscess most commonly occurs in middle aged adults between 40’s and 50’s.

Pyogenic liver abscess is more common among men compared to women (3.3 vs. 1.3 per 100,000).^[3][4]

80% of all liver abscesses in developed countries are pyogenic liver abscess.

Common risk factors in the development of pyogenic liver abscess are immunodeficiency, diabetes mellitus, pancreatic or hepatobiliary disease and liver transplant.^[1][2][3][4]

Common risk factors in the development of pyogenic liver abscess are:^[1][2][3][4]

• Immunodeficiency
• Diabetes mellitus
• Pancreatic or hepatobiliary disease
• Liver transplant

According to the U.S. Preventive Service Task Force (USPSTF), there is insufficient evidence to recommend routine screening for pyogenic liver abscess.

According to the U.S. Preventive Service Task Force (USPSTF), there is insufficient evidence to recommend routine screening for pyogenic liver abscess.

If left untreated, pyogenic liver abscess may progress to peritonitis or pleuritis secondary to rupture of the abscess into peritoneal or pleural cavities and sepsis.^[1][2][3]Complications of pyogenic liver abscess include septicemia, intra-abdominal abscess, hepatic failure, renal failure, recurrent liver abscess and free peritonitis.^[4]The prognosis of liver abscess depends on underlying risk factors such as advanced age, malignancy, jaundice, multiple abscesses, hemoglobin <10g/dl and elevated blood urea nitrogen.^[5]

If left untreated, pyogenic liver abscess may progress to peritonitis or pleuritis secondary to rupture of the abscess into peritoneal or pleural cavities and sepsis leading to death.^[1][2][3]

Complications of pyogenic liver abscess include:^[4]

• Septicemia
• Intra abdominal abscess
• Hepatic failure
• Renal failure
• Recurrent liver abscess
• Massive upper gastrointestinal bleed
• Prolonged biliary drainage
• Free peritonitis

• The prognosis has improved markedly with early diagnosis, drainage and long term antibiotic therapy.^[6]
• If left untreated abscess ruptures leading to death.
• The prognosis of pyogenic liver abscess depends on underlying risk factors such as^[5][7][1]

• Advanced age
• Malignancy
• Shock
• Jaundice
• Multiple abscesses
• Hemoglobin <10 g/dL
• Elevated blood urea nitrogen