Ameboma, the forgotten granuloma?

Consider a cyst that occupies space and feeds off red blood cells ... giving rise to purulent matter resulting in dessemination and abscess formation. You are encouraged to think critically about what you find here. Do your own research if you still have questions.

Amebiasis is a disease caused by a one-celled parasite called Entamoeba histolytica (ent-a-ME-ba his-to-LI-ti-ka). There are a number of variants.

In the Canada and the United States, amebiasis is most often found in immigrants from developing countries. It also is found in people who have traveled to (or who have come into contact with) developing countries, such as Mexico.

The symptoms often are quite mild and can include loose stools, stomach pain, and stomach cramping. Amebic infection is a severe form of amebiasis associated with stomach pain, bloody stools, and fever. Rarely, E. histolytica invades the liver and forms an abscess. Even less commonly, it spreads to other parts of the body, such as the lungs or brain, and cause abscesses. It may produce symptoms that mimic a number of intestinal disease processes, including cancer.

The infection may mimic space-occupying lesions in CNS, and the infected patient may present with hemiparesis, aphasia or seizures. In such instances, head CT and MRI may reveal ring-enhancing lesion (abscesses) suggestive of brain tumors. Parasitic cysts of any origin may mimic primary or metastatic brain tumor(s).

Clinical Features:
A wide spectrum, from asymptomatic infection ("luminal amebiasis"), to invasive intestinal amebiasis (dysentery, colitis, appendicitis, toxic megacolon, amebomas), to invasive extraintestinal amebiasis (liver abscess, peritonitis, pleuropulmonary abscess, cutaneous and genital amebic lesions). An ameboma may mimic carcinoma of the colon.


Pleuropulmonary amebiasis is the common and pericardial amebiasis the rare form of thoracic amebiasis. Pleuropulmonary amebiasis is easily confused with other illnesses and is treated as pulmonary TB, bacterial lung abscesses, and carcinoma of the lung, which may exacerbate the condition.

Amebiasis is caused by the protozoan parasite. Protozoan infections include amebiasis, toxoplasmosis, and trypanosomiasis (sleeping sickness). Protozoa can produce malaria, amebiasis, leishmaniasis and trypanosomiasis.

Typically, N fowleri produces primary amebic meningoencephalitis (PAM), which is clinically indistinguishable from acute bacterial meningitis.

The cyst fills with bacteria and pus, and becomes an abscess (chocolate-brown abscess fluid is thought to be highly characteristic of amebic abscess); the earliest amoebic lesions appear as small, yellow mucoid (yellowish exudate) elevations containing necrotic material where the parasite can be found. The center of an amebic abscess, consisting of lysed hepatocytes, erythrocytes, bile and fat, may liquify and this necrotic material (sometimes incorrectely called pus) will range in color from yellowish to reddish brown. If the abscess bursts inside the body, there is a risk of blood poisoning (septicaemia). Septicemia, is a form of sepsis.

The most common signs of amebic infection are alternating diarrhea and constipation(possibly accompanied by blood and excessive mucus) and irregular appetite. Other clinical signs include vomiting, listlessness,weakness, low weightand signs of dehydration (e.g.sunken eyes, thick oral mucus). If the lungs are infected (a condition generally associated with more chronic infections), labored breathing, mouth/nasal discharge and wheezing may also be noted.

In the Canada and the United States, amebiasis is most often found in immigrants from developing countries, such as Mexico. It also is found in people who have traveled to (or who have come into contact with) developing countries and in people who live in institutions that have poor sanitary conditions which pose health issues for travelers.

Ameba only multiplies rapidly if a person is very run down by an immune deficiency, illness or infection. Only virulent amoeba can lyse polymorphonuclear leukocytes (PMNs).

Ameba can spread hematogeneously from a cutaneous, ocular, or pulmonary lesion to the CNS, where vasculitis may also dominate the clinical picture.

An ameboma may simulate an "adenocarcinoma" or another granulomatous process. Parasitic cysts of any origin may mimic primary or metastatic brain tumor(s).