The formation of a hepatic abscess is not an uncommon finding. The types of abscesses found include pyogenic (bacterial infections), amebic (secondary to Entamoeba histolytica), and fungal etiologies. Ecchinococcal infections may result in the formation of hepatic cysts, and should be considered in persons from endemic areas who have contact with livestock and dogs. Abscess formation may result from hematogenous spread from distal sites or from infections and disease within the peritoneal cavity (appendicitis, diverticulitis, cholangitis, acute cholecystitis, or malignancies of the pancreas, ampulla, and common bile duct). Abscess formation may be single or multiple in number and most are found in the right lobe of the liver. Pyogenic hepatic abscess formation is also a postsurgical complication of liver transplantation
Symptoms of hepatic abscess include fever, chills, anorexia, weight loss, nausea, and vomiting. Approximately half of patients will have symptoms consistent with liver disease to include jaundice, hepatomegaly, or right upper quadrant tenderness. Because symptoms are so nonspecific, radiographic studies of the abdomen should be pursued in cases of fever of unknown origin. Right upper quadrant ultrasonography is frequently employed and is very sensitive. When ultrasound examination is inconclusive, CT scanning may prove helpful. It is of note that often times a right pleural effusion, right lower lobe atelectasis, or an elevated right hemidiaphragm may be noted on chest radiography thus prompting a workup and leading to the diagnosis.
Laboratory abnormalities are also minimal. An elevated alkaline phosphatase level is common with minimal elevations of serum transaminases occurring less frequently. Leukocytosis is often noted as is a normocytic anemia, hyperbilirubinemia, and hypoalbuminemia.
PYOGENIC INFECTION
Pyogenic hepatic abscess formation results from hematogenous seeding from distant sites, or infections located within the peritoneal cavity may travel to the liver via the portal venous blood flow. Multiple small abscesses involving multiple lobes of the liver implicate biliary disease as the source. Because portal blood flow is directed toward the right lobe, abscesses localized to the right lobe should be considered to have originated from disease within the peritoneal cavity (diverticulitis, Crohns disease, ulcerative colitis, or bowel perforation). Some infections are cryptogenic with no identifiable source. Infections are often polymicrobial resulting from infection by aerobic (gram-negative and gram-positive), anaerobic, and microaerophilic organisms. Klebsiella pneumoniae is the most common etiologic agent. Blood cultures and culture of purulent aspirates should be obtained. Persons with Klebsiella liver abscess may have associated meningitis, brain abscess, endophthalmitis, septic pulmonary emboli, or portal vein thrombosis. Therapy entails drainage (percutaneous or if necessary surgical) along with an aminoglycoside and either a second or third generation cephalosporin or an extended-spectrum beta lactam. Fluoroquinolones may also be used. Once sensitivities are obtained, therapy should be directed accordingly. A fungal cause should be considered in patients with systemic fungal infections especially in the immunocompromised patient.
AMEBIC INFECTION
Entamoeba histolytica but not E. dispar or E. moshkovskii is a pathologic protozoa which can cause disease in humans. Most infections are asymptomatic. Infection ranges from colitis which in extreme cases may be fatal (extensive fulminant necrotizing colitis) to abscess formation commonly of the right hepatic lobe. Amebic abscess should be considered in younger adult patients and patients with a history of travel to endemic areas. Amebic abscess can occur months to years after exposure; therefore, a historical time line can actually interfere with the diagnosis and the disease should be considered whenever symptoms dictate. Hepatic infection usually occurs in the absence of symptoms consistent with dysentery. When hepatic abscess is a consideration, radiographic confirmation should be pursued. Ultrasonography is a good initial test; however, if it is inconclusive, CT or MRI may be necessary. Complications of infection include pleuropulmonary disease (effusion, empyema, atelectasis, and hepatobronchial fistula), pericardial amebiasis, and intraperitoneal rupture of the abscess. Rare complications include brain abscess formation or genitourinary infection.
Amebic titers should be sent on all patients with hepatic abscesses. Positive titers are extremely sensitive for invasive amebic infection and are not seen in the asymptomatic carrier. Serologic tests may take up to 1 week after infection to become positive. Therefore, in patients with symptoms for less than 7 days, a repeat serology should be performed 5 days after the initial study if the diagnosis is still in doubt. Testing for concomitant intestinal disease should be performed. Stool samples may be sent for ova and parasite screens although light microscopy can not differentiate E. histolytica from non-pathologic strains. Futher testing of the stool specimen for E. histolytica antigen will establish whether intestinal disease exists.
Treatment for hepatic amebic abscess entails metronidazole (750 mg TID for 10 days). If stool cultures are positive for intestinal infection an agent active against intestinal infection (iodoquinol 650 mg TID for 20 days) should be administered concurrently. Hepatic amebic abscesses should not be subjected to aspiration unless bacterial infection is still suspected, appropriate therapy with metronidazole proves ineffective or the abscess is so large as to cause pain or impending rupture is anticipated. An anchovy paste appearing aspirate is commonly obtained upon aspiration.