Discussion:

Amebic liver abscesses is one of the most common extraintestinal manifestations of E. histolytica, a protozoa that can enter the portal system from the colon. Most infections are acquired through ingestion of cysts from fecally contaminated food or water. The cyst passes to the small intestine where it excysts. The trophozoite divides and moves into the large intestine. The majority encyst and are passed through feces, but some amoeba can attach to and invade mucosal tissue and disseminate through the body. In some of these cases, the invasion causes the mucosal tissue forming "flask-shaped" lesions.

On microscopy, the nuclei of E. histolytica will be small, discrete, and usually centrally located karyosome. The peripheral chromatin is evenly distributed and uniform in size. The trophozoite has a single nucleus and is usually 15-30 micrometers in diameter; size is an important differentiating point from E. hartmanni. Phagocytosis of erythrocytes is rare, but pathognomonic. The cyst form is spherical with a refractile wall. The cytoplasm has dark staining chromatoidal bodies and 1-4 nuclei.

Patients typically present with fever, RUQ pain, and travel to an endemic area. Diagnosis can be sufficiently made with proper examination of stool specimen. Serological testing and EIA antigen detection tests are also available. Metronidazole is the treatment of choice.