Pyogenic liver abscess is an uncommon but important disease, which is usually fatal unless prompt diagnosis allows early treatment. Despite advances in diagnostic techniques and in antibiotic therapy, the mortality rate associated with pyogenic liver abscess is still high. Diagnosis may not be made until after death, because of the non-specific nature of the disease. The physician therefore needs to be alert to the possibility of pyogenic liver abscess when evaluating patients with fever of unknown origin. In countries where Entamoeba histolytica is endemic, a liver abscess is much more likely to be amoebic than pyogenic.

It is difficult to determine the true incidence of pyogenic liver abscess. The frequency determined from autopsy reports varies between 0.29 and 1.47 per cent, while the incidence in the hospital population ranges from 0.008 to 0.016 per cent. In 1938 the average patient age was in the fourth decade; today pyogenic liver abscess predominantly affects those in the fifth and sixth decades.

Fever and abdominal pain are the most common symptoms of pyogenic liver abscess. About 90 per cent of patients experience a spiking fever, which may be followed by chills. Abdominal pain is usually located in the right upper quadrant, and may radiate to the right shoulder or right flank. Epigastralgia or upper abdominal pain may also occur. A ruptured abscess will cause acute diffuse abdominal pain. Non-specific symptoms such as nausea, vomiting, anorexia, and malaise occur with varying frequency.

Hepatomegaly with tenderness in the right subcostal region is the most common physical sign, although its incidence has decreased from 80 per cent to about 50 per cent. Clinically obvious jaundice occurs in one-third of patients and usually indicates biliary tract disease with cholangitis and possible multiple liver abscess; it is considered a grave sign. The symptoms and signs are similar to those of biliary tract diseases such as cholangitis, choledocholithiasis, or even acute cholecystitis. Meticulous differential diagnosis is necessary to facilitate early treatment.

Ultrasonography has a reported sensitivity for detecting liver abscess in the range of 85 to 95 per cent. It may be the initial test undertaken to exclude a suspected liver abscess. This technique is non-invasive, avoids radiation exposure, differentiates solid from fluid-filled masses, and is relatively inexpensive. CT also has a 95 to 100 per cent sensitivity for liver abscesses: solitary or multiple abscesses as small as 0.5 cm may be detected by this technique. CT scanning (Fig. 2) 2670 will define a liver abscess when ultrasound findings are equivocal. Liver scans have been replaced by ultrasonography: although ultrasonography cannot differentiate solid from cystic masses, it has an accuracy of 80 to 95 per cent. Angiography is recommended only when a febrile type of hepatoma needs to be distinguished from a liver abscess. Most abscesses (60 per cent) are located in the right hepatic lobe. Multiple abscesses and solitary abscesses are equally common.

Pyogenic liver abscess is easily diagnosed by echographic imaging, which reveals a cystic lesion of irregular contour. Confirmation is obtained when purulent fluid is obtained on ultrasound-guided percutaneous aspiration. The diagnosis can also be made directly at surgery. Pus and the wall of the abscess must be negative for Entamoeba histolytica, and levels of antibody to this organism, measured by the indirect haemagglutination test, should be less than 128.

Microabscess, a special entity of pyogenic liver abscess, is secondary to suppurative cholangitis, and its clinical features are similar to those of pyogenic liver abscess. Cholangiography shows an abscess with fig-like club-leaves communicating with the biliary tree. It is usually cured by percutaneous transhepatic biliary drainage and antibiotics.

Laboratory investigation does not contribute to the diagnosis. Leucocytosis is present in over 80 per cent of patients, and anaemia is usually present. Varying degrees of abnormality are seen in liver function tests, but these are non-specific. The serum level of alkaline phosphatase is elevated in about 90 per cent of patients. Hyperbilirubinaemia is found in 30 to 50 per cent of patients, and hypoalbuminaemia is present in one-third. This may be an indication of a serious underlying intrahepatic lesion or chronic infection.

Chest radiographs are abnormal in 28 to 70 per cent of patients, showing a elevation of the diaphragm, effusion, infiltration, or atelectasis. Pleural effusion, occurring in 20 to 40 per cent of patients, may indicate a subphrenic inflammatory process. When fever and pleural effusion are present, meticulous abdominal sonography or a CT scan is required to rule out the progression of liver abscess.

Pyogenic liver abscess may originate from biliary tract disease, portal vein, liver trauma, malignancy, direct invasion, hepatic artery, or cryptogenic origins (Table 1) 633. Biliary tract disease is the most common cause, accounting for 33 to 55 per cent of patients in a recent series. Abscesses that develop from the portal vein (16 to 30 per cent) are generally related to diverticulitis, appendicitis, or pancreatic abscess. Malignancy, perhaps hepatoma itself, causes 8 to 22 per cent of pyogenic liver abscesses; these have a higher mortality rate. Sepsis may cause liver abscess by haematogenous spread through the hepatic artery: four cases of liver abscess secondary to dental abscess, transmitted by this means, have been reported. Pyogenic liver abscess follows liver trauma in 1 to 12 per cent of patients. It is usually caused by superimposed bacterial infection of traumatically devitalized liver tissue in a poorly drained lesion. The incidence of cryptogenic liver abscess has fallen because of advances in diagnostic techniques.

The most commonly isolated organism is E. coli. Recently however, some authors have reported that Klebsiella is becoming more common.

Gram-positive aerobes such as staphylococcus and streptococcus are usually isolated from pus. Polymicrobial infection is present in about 22 per cent of patients, and such patients usually have a higher mortality rate.

The number of anaerobic organisms cultured has steadily increased due to improved microbiological techniques: 19 to 45 per cent of patients are infected by anaerobic bacteria. Successful treatment requires appropriate drug therapy. Mortality rates as low as 5 per cent can be obtained after successful isolation of anaerobic organisms.

Complications of pyogenic liver abscess are not unusual, and increase the mortality rate. Rubin et al. reported fatal complications in 10 of 14 patients (71.4 per cent) with pyogenic liver abscess. Patients with respiratory complications have statistically significant higher mortality rates.

Complications include spontaneous rupture of the abscess. Rupture of the abscess into the abdominal cavity may cause generalized peritonitis, necessitating prompt surgical intervention; this occurs in 6 to 10 per cent of patients. An abscess rupturing into the lungs may cause pyothorax or hepatobronchial fistula: Pitt and Zuidema reported pleuropulmonary changes in 15 per cent of their patients. Subphrenic abscess or subhepatic abscess has been reported in 8 to 10 per cent of patients. Septicaemia occurs in 45 per cent of patients, and is usually fatal. Rare complications include renal failure, meningitis, and rupture into the pericardium, retroperitoneum, or small intestine.

Although antibiotics alone have been reported to cure pyogenic liver abscess, drainage either by surgery or by the percutaneous route is usually considered necessary.

Percutaneous catheter drainage has been used for about 10 years, and is now the first line of treatment. Percutaneous drainage performed under ultrasonographic guidance also allows a definitive diagnosis to be made by the demonstration of purulent fluid in the aspirate. The abscess cavity should then be drained by an indwelling catheter. Clinical features such as fever, abdominal pain, and leucocytosis are promptly relieved as the pus is drained and pressure in the abscess cavity is reduced. Percutaneous drainage has several advantages: it is simple and safe, and can usually be performed at the bedside and completed in few minutes; the procedure is performed under local anesthesia, avoiding surgical or anaesthetic risks in elderly or high-risk patients; multiple catheters can be installed for multiple abscesses; and reduction of pressure within the abscess cavity by continuous drainage improves blood flow to the adjacent compressed hepatic parenchyma, and enhances the efficacy of antibiotic therapy. The possibility of echinococcal cysts should be excluded before percutaneous drainage is planned, especially when patients are in or from an endemic area.

Surgical drainage should be performed only when percutaneous abscess drainage fails. Such failure may be due to the small calibre of the drainage tube or the high viscosity of the pus. In order to ensure a smooth drainage, a tube of larger bore must replace the previously inserted tube. Surgical intervention is also required if a pyogenic liver abscess ruptures. This usually causes acute abdominal pain. Emergency laparotomy to clean the abdominal cavity and drain the abscess is mandatory. Laparotomy also allows perforation of a hollow organ to be excluded. Surgery is also necessary when the abscess has spread from an abdominal organ. Biliary surgery should be performed in the presence of biliary stones or stricture. Diseases of the gastrointestinal tract must be treated in addition to the management of the abscess.

Transperitoneal drainage is now used frequently, since it permits assessment and correction of aetiological factors. The abscess is completely evacuated and the roof is usually partially excised. Drains are left in the cavity and others are left in the subhepatic space or adjacent to the abscess cavity. Specimens from the abscess cavity or abscess wall must be examined by a pathologist to exclude the possibility of hepatoma or amoebiasis. A febrile type of hepatoma mimics pyogenic liver abscess, and usually causes a failed percutaneous drainage.

A posterior superiorly located solitary abscess can be drained by a posterior extraperitoneal approach, which had the advantage of being simple and safe, especially in critically ill patients. It also prevents purulent fluid from draining into the abdominal cavity.

Either surgical or percutaneous drainage should be complemented by antibiotic therapy. Broad-spectrum antibiotics combined with aminoglycoside are given initially, and changed according to the results of bacterial cultures and sensitivity tests.

An untreated liver abscess is associated with a mortality rate of up to 79 per cent. However, there has been a significant decrease in mortality in recent years as a result of advances in diagnostic technique and improvements in antibiotic treatment and early drainage. In the past decade, the reported mortality rate has ranged from 11.5 to 40 per cent, with a mean of about 20 per cent. Factors that have been recognized as causing a higher mortality rate include the presence of multiple abscesses, hypoalbuminaemia (less than 2.5 g/dl), impaired liver function, leucocytosis greater than 20 000 mm3;, and pleural effusion.

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