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 Table of Contents  
Year : 2021  |  Volume : 41  |  Issue : 1  |  Page : 45-48

Unusual case of huge rectal ameboma mimicking a rectal carcinoma in a taiwanese traveler

1 Department of Surgery, National Defense Medical Center, Tri-Service General Hospital, Taipei City, Taiwan
2 Department of Pathology, National Defense Medical Center, Tri-Service General Hospital, Taipei City, Taiwan
3 Department of Surgery, Division of Colorectal Surgery, National Defense Medical Center, Tri-Service General Hospital, Taipei City, Taiwan
4 Department of Surgery, Division of Colorectal Surgery, National Defense Medical Center, Tri-Service General Hospital; Department of Surgery, Division of Colon and Rectal Surgery, National Defense Medical Center, Tri-Service General Hospital, Songshan Branch, Taipei City, Taiwan
5 Department of Surgery, Division of Colorectal Surgery, National Defense Medical Center, Tri-Service General Hospital; National Defense Medical Center, Graduate Institute of Medical Sciences; National Defense Medical Center, School of Medicine, Taipei City, Taiwan

Date of Submission26-Apr-2020
Date of Decision25-May-2020
Date of Acceptance28-May-2020
Date of Web Publication25-Jul-2020

Correspondence Address:
Dr. Je-Ming Hu
Department of Surgery, Division of Colorectal Surgery, National Defense Medical Center, Tri-Service General Hospital, No. 325, Section 2, Cheng-Kung Road, Neihu District, Taipei City 11490
Dr. Shu-Wen Jao
Department of Surgery, Division of General Surgery, Tri-Service General Hospital, NO. 325, Section 2, Cheng-Kung Road, Taipei 114
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jmedsci.jmedsci_111_20

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Invasive protozoan infection with ameboma formation is relatively rare in advanced-modern countries and can be mistakenly diagnosed as a neoplasm, which constitutes the majority of conditions in medical centers. The treatment between rectal ameboma and carcinoma is different, in which the former can be treated by effective medication, and the latter may sustain invasively inconvertible surgical intervention. Herein, we present a case of a 66-year-old man with a travel history to Japan who presented with anal pain and diarrhea secondary to ulcerative rectal mass detected by colonoscopy, which resembled colorectal carcinoma. The mass lesion was later determined histopathologically to be amebic infection caused by invasive Entamoeba histolytica, which had remarkable regression after metronidazole therapy. This case highlights the necessity of complete recognition of ulcerative rectal mass before definitive treatment and inadvertent clues from travel history to achieve a good outcome.

Keywords: Rectal ameboma, Entamoeba histolytica, rectal neoplasm, medical therapy, Taiwanese traveler

How to cite this article:
Lin GH, Lin YC, Yu CW, Lin TC, Pu TW, Jao SW, Hu JM. Unusual case of huge rectal ameboma mimicking a rectal carcinoma in a taiwanese traveler. J Med Sci 2021;41:45-8

How to cite this URL:
Lin GH, Lin YC, Yu CW, Lin TC, Pu TW, Jao SW, Hu JM. Unusual case of huge rectal ameboma mimicking a rectal carcinoma in a taiwanese traveler. J Med Sci [serial online] 2021 [cited 2021 Feb 28];41:45-8. Available from: https://www.jmedscindmc.com/text.asp?2021/41/1/45/290725

  Introduction Top

Amebiasis is an infectious disease caused by the protozoan Entamoeba histolytica, which may potentially evolve into invasive colitis and ameboma, mimicking colorectal carcinoma. Colorectal amebiasis clinically ranges from asymptomatic carrier to severe necrotizing colitis with bleeding or perforation, which had similar features with carcinoma, or even rarely presents with focal ileocolonic intussusceptions, in which ameboma played a vital role.[1],[2] Determining the high index of clinical suspicion of this disease entity, distinguishing it from other more common causes of rectal masses, and instituting appropriate therapy play important roles in the precise treatment of the disease. We currently review the literature on the pathogenesis of invasive E. histolytica infection and ameboma formation and management of this disease in the neoteric generation.

  Case Report Top

A 66-year-old man without any previous systemic disease presented with rectal tenesmus, severe anal pain, bloody stool, and diarrhea for 3 months with gradual deterioration. He had a travel history to Japan and consumed sashimi 3 months ago. On digital rectal examination, a palpable annular tumor was noted at the lower rectum localized 2–4 cm above the anal verge. Abdominal computed tomography was also performed, which revealed full-thickness rectal wall [Figure 1]. The colonoscopic view [Figure 2] showed an annular ulcerative tumor with lumen narrowing 2–4 cm above the dentate line, which highly suggested of carcinoma. Moreover, random biopsy was performed, which did not provide consistent results of malignant cells. Due to high suspicion of malignancy, repeated biopsy was performed, which histopathologically revealed granulation tissue characterized by vascular proliferation, chronic inflammation, and fibrosis with ulcer, indicating amebiasis of the rectal tissue [Figure 3]. Finally, rectal ameboma was confirmed. He had an uneventful recovery with metronidazole therapy prescribed after the diagnosis, and the symptoms subsided 10 days after the treatment 2 months later. Follow-up colonoscopy demonstrated remarkable regression of the rectal lesion [Figure 4]. This case highlights the importance of complete recognition of ulcerative rectal mass before further treatment.
Figure 1: Computed tomography of the abdomen revealed focal thickening of the rectal wall

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Figure 2: Colonoscopic view revealed an ulcerative annular tumor at the lower rectum approximately 2 cm above the dentate line, negative to the sigmoid colon

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Figure 3: Histopathological examination on rectal biopsy revealed numerous Entamoeba histolytica trophozoites, H and E, stained. Arrows indicate examples of trophozoites with visible nuclei; typical small, central karyosomes; and fine peripheral chromatin

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Figure 4: Follow-up colonoscopy after metronidazole therapy demonstrated remarkable regression of the previous ulcerative rectal lesion

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  Discussion Top

E. histolytica is well recognized as a pathogenic ameba associated with intestinal and extraintestinal infections, which is among the related protozoan species that, on the contrary, are asymptomatically silent. E. histolytica may cause locally invasive diseases, such as luminal amebiasis and amebic colitis, with penetration of the organism into the intestinal mucosa, and the most common symptom is severe dysentery. Regarding severe chronic infections, it may lead to further complications such as peritonitis, perforations, and even formation of amebic granulomas, such as ulcerative intestinal sections with inflammatory response, so-called ameboma.[3] As for extraintestinal amebiasis, amebic liver abscesses are the most common manifestations by metastasis through the portal vein, and more rarely, penetration of a liver abscess into pleura, lungs, and pericardium and necrotic lesions on the perianal skin and genitalia are also noted.[4] Statistically, the majority of amebiasis occurs in developing countries; in contrast, risk factors include recent travel history, anoreceptive intercourse, and immunocompromised and institutionalized populations in industrialized countries. However, several studies disclosed that sporadic cases occurred in developed countries.[2] Ingestion of contaminated food and water is the most common mode of transmission, and venereal transmission through the fecal-oral route is also observed. The standard method for diagnosis of intestinal amebiasis is stool examination by microscopy, in which morphologic differentiation is potentially complicated based on characteristics of the cysts and trophozoites, leading to the need of consecutive stool samples due to its low sensitivity. Detection of specific antibody (immunoglobulin G) in serologic tests can be extremely valuable in confirming invasive amebic disease of the colon or extraintestinal amebiasis.[4]

Patients with long-term infection may develop ulcerative, exophytic, and inflammatory amebomas that are indistinguishable from carcinomas due to its pseudotumor-like presentation.[5],[6] The annular colonic granulation tissue forms at single or multiple sites and usually within the cecum or ascending colon. On the contrary, it is rarely detected when it presents at the rectum. The clinical symptoms of amebomas have low specificity and clinically range in severity from mild diarrhea, constipation, cramping abdominal pain, tenesmus, or associated systemic symptoms, including weight loss and fever, to life-threatening fulminating necrotic colitis with perforation and development of amebic peritonitis, which are the main causes of death in invasive intestinal amebiasis.

However, the palpable ulcerative mass and bloody diarrhea may be more likely considered as features of colorectal malignancy or inflammatory bowel disease, and neither of them have treatment identical to that of invasive amebiasis. Misdiagnosis and corticosteroid treatment can be fatal in invasive amebiasis, and surgical intervention is believed to inadequate and irrelevant.

Metronidazole and related 5-nitroimidazole compounds are the drugs of choice in the treatment of invasive amebiasis due to their efficient absorption in the small intestine and high concentrations in the tissues.[4] Hamilton et al. reported a series of 71 cases of ameboma, in which 42 were totally cured medically and a 17% mortality in the remaining cases (29) of the surgical group,[7] illustrating the importance of treatment choice. As a result, colonic evaluation of suspected amebiasis is of diagnostic value when accompanied by biopsy and microscopic identification of Entamoeba species.[3]

Although human rectal ameboma is rare in Taiwanese individuals, the increasing activities for worldwide ecotourism of Taiwanese travelers enhance the risk of acquiring infection caused by the parasite E. histolytica. This report presents an unusual case of rectal ameboma in Taiwan. Awareness of rare gastrointestinal symptoms should be considered in a patient who has a rectal lesion and recently returned from abroad. Most important part, an experienced colorectal surgeon should be alerted for second confirmation once the lesion revealed malignancy-liked appearance by naked-eye detection initially but reported completely inconsistent microscopically ultimately. This rare presentation highlights the great necessity of a thorough recognition before the treatment of an ulcerative rectal mass to achieve an accurate and exceptional outcome.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient has given his consent for his images and other clinical information to be reported in the journal. The patient understands that his name and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.


We would like to thank the patient for allowing us to share her details.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Steer S, Clarke DL, Buccimazza I, Thomson SR. An unusual complication of intestinal amoebiasis. S Afr Med J 2005;95:845.  Back to cited text no. 1
Ooi BS, Seow-Choen F. Endoscopic view of rectal amebiasis mimicking a carcinoma. Tech Coloproctol 2003;7:51-3.  Back to cited text no. 2
Lee KC, Lu CC, Hu WH, Lin SE, Chen HH. Colonoscopic diagnosis of amebiasis: A case series and systematic review. Int J Colorectal Dis 2015;30:31-41.  Back to cited text no. 3
Warhurst DC. Amebic infections. In: Cohen J, Opal SM, Powderly WG, editors. Infectious Diseases. 3rd ed.., Ch. 110. London: Content Repository Only!; 2010. p. 1148-53.  Back to cited text no. 4
Simşek H, Elsürer R, Sökmensüer C, Balaban HY, Tatar G. Ameboma mimicking carcinoma of the cecum: Case report. Gastrointest Endosc 2004;59:453-4.  Back to cited text no. 5
Hardin RE, Ferzli GS, Zenilman ME, Gadangi PK, Bowne WB. Invasive amebiasis and ameboma formation presenting as a rectal mass: An uncommon case of malignant masquerade at a western medical center. World J Gastroenterol 2007;13:5659-61.  Back to cited text no. 6
Hamilton HE. Treatment of amebiasis. Arch Internal Med 1954;94:612-7.  Back to cited text no. 7


  [Figure 1], [Figure 2], [Figure 3], [Figure 4]


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