Description, Causes and Risk Factors:
A nodular, tumor-like focus of proliferative inflammation sometimes developing in chronic amebiasis, especially in the wall of the colon.
Ameboma occurs most commonly in the cecum. It cannot be distinguished Radiologically from cancer, giving rise to an important problem, as attested by a number of postoperative deaths in the presence of unsuspected Ameboma. The intestinal protozoan parasite Entamoeba histolytica (a species of ameba that is the only distinct pathogen of the genus, the so-called “large race” of Entamoeba histolytica, causing tropical or amebic dysentery in humans and also in dogs. In humans, the organism may penetrate the epithelial tissues of the colon, causing ulceration; in a small proportion of these cases, the organism may reach the liver by the portal bloodstream and produce abscesses (hepatic amebiasis); in a fraction of these cases it may then spread to other organs, such as the lungs, brain, kidney, or skin) is the causative organism responsible for human ameboma in most cases.
The prevalence of infestation with ameboma is greater in the tropics than in temperate or arctic zones but the incidence of infestation by endoameba histolytica is by no means analogous to the incidence of the disease known as amebiasis. Ameboma in the USA usually is a chronic, low-grade, dormant disease, often without diarrhea. For the latter reason many cases are attributed to functional disturbance.
An experimental study was carried out in 48 guinea pigs arranged into four groups, to assess the role of hypersensitivity in formation of ameboma. Repeated intracecal inoculations of saline in Group I and mixed amebic and bacterial suspension in other groups were made. Animals in Group 111 were sensitized by amebic antigen and in Group IV by bacterial antigen before inoculations. Lesions produced in the amebic hypersensitive group of animals were notably different from those in other groups. A higher frequency of cecal ulceration and a significantly severe grade of cecal damage was seen in these animals. Extensive pericecal adhesions and marked thickening of the wall produced nodular lesions. Granulomas were formed with dense chronic inflammatory cell infiltration including fibroblasts.
The disease may manifest itself in three ways, a mass in the region of the cecum which may mimic an appendix abscess, an ulcer in the rectum which mimics carcinoma and a stenosing mass in the course of the colon which precipitates intestinal obstruction.
The standard method for diagnosis of amebomais examination of stools by microscopy.However, the reported sensitivity of this method foridentifying amebic organisms ranges from 25% to 60%.False-positive results may also occur because E. histolyticais morphologically identical to non-pathological species,namely, Entamoeba dispar and Entameba moshkovskii.Currently, more sensitive and specific methods, includingantigen detection in stools and serum, and polymerasechain reaction (PCR) techniques are now utilized.
Researchers found 21 suspicious cases in a review of 300 barium enema examinations. In 12 of the 21 cases, E. histolytica was found in the stools. It was the opinion of these investigators that roentgenologic study of the' colon is the most valuable method of finding amebic disease of the colon. The significant roentgenologic changes in the cecum as described by these observers consisted of spasm, dilatation, relaxation, and abnormal patency of the ileocecal valve; inflammatory induration with "coning" and inflammatory tumefactive defects.
The primary treatment for ameboma is oral anti-amebic therapy. Longer intervals of therapy may be warranted in cases more severe cases of ameboma formation. Surgical intervention is rarely indicated except for rare instances of acute necrotizing colitis with bowel perforation, or if the patient fails to respond to medical therapy.
NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.
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