Amebic Liver/Hepatic Abscess

Amebic liver abscess results from Entamoeba histolytica trophozoites reaching the liver via the portal circulation following intestinal invasion, causing a characteristic single, large abscess (typically right lobe) filled with "anchovy paste"-like necrotic material, distinct from bacterial (pyogenic) liver abscess in both typical presentation and management.

It is the most common extraintestinal manifestation of amebiasis.

• Fever, right upper quadrant pain (often with tenderness and, sometimes, referred right shoulder pain from diaphragmatic irritation), hepatomegaly, and weight loss, typically over days to a couple of weeks.

• A history of concurrent diarrhea is present in only a minority, since the intestinal infection may have resolved or been asymptomatic before hepatic spread.

Rupture (into the pleural space, pericardium, or peritoneum) is a serious complication.

• Ultrasound or CT shows a well-defined, typically single, hypoechoic/hypodense lesion, most commonly in the right lobe.

• Serology (amebic antibody testing) is positive in the large majority of cases and is highly useful diagnostically, though it can remain positive for years after past infection in endemic populations, requiring clinical correlation.

• Stool microscopy for E. histolytica trophozoites or cysts is positive in only a minority given the frequent absence of concurrent active intestinal disease.

• Aspiration is not routinely required for diagnosis but may be performed for large abscesses, diagnostic uncertainty, or failure to respond to medical therapy, typically yielding characteristic reddish-brown, odorless "anchovy paste" fluid.

• Metronidazole 750 mg PO/IV tds for 7 to 10 days is first line, highly effective, with clinical improvement typically within 3 to 5 days
• Followed by a luminal agent (paromomycin 25 to 35 mg/kg/day PO in 3 divided doses for 7 days, or diloxanide furoate where available) to eradicate any residual intraluminal cysts and prevent relapse or continued transmission, since metronidazole alone does not reliably clear luminal infection
• Aspiration or drainage is reserved for large abscesses (over 5 to 10 cm, given higher rupture risk), left lobe abscesses (higher risk of pericardial rupture), failure to improve clinically within 3 to 5 days of antibiotics, or diagnostic uncertainty where pyogenic abscess cannot be excluded
• Most abscesses resolve on imaging over weeks to months even after clinical resolution; routine repeat imaging to confirm complete radiological resolution before stopping follow-up is not required if the patient is clinically well

Referral: infectious disease/gastroenterology; interventional radiology for drainage where indicated.