Year : 2009 | Volume
: 52 | Issue : 2 | Page : 228--230
Ameboma of the colon with amebic liver abscess mimicking metastatic colon cancer
Hilda Fernandes1, Clement R.S D'Souza2, GK Swethadri1, CN Ramesh Naik1,
1 Department of Pathology, Fr Muller Medical College, Mangalore, Karnataka, India
2 Department of Surgery, Fr Muller Medical College, Mangalore, Karnataka, India
Department of Pathology, Fr Muller Medical College, Mangalore - 575 002
Amebic colitis is common in developing countries, with its variable and non-specific symptoms. Amebomas occur rarely, resulting from the formation of annular granulation tissue, usually in the cecum and in the ascending colon. This report describes the case of a 59-year-old male who presented with abdominal pain. Radiological examination depicted concentric thickening of the cecal wall with mass formation and a cystic lesion in the liver. The endoscopy performed showed a growth in the ascending colon. Biopsy revealed extensive necrosis and inflammatory cells. The patient was referred to this hospital for surgical treatment with a provisional diagnosis of carcinoma of the colon. Peroperatively, a cecal mass was identified. However, suspected secondaries were not seen on the surface of the liver. Histological examination of the right hemicolectomy specimen revealed cecal and ascending colon amebomas. Trophozoites of Entamoeba histolytica were better recognized after periodic acid-Schiff staining. Treatment with Metronidazole for 2 weeks followed by diloxanide furoate for an additional 2 weeks was administered. The liver lesion resolved completely after 8 weeks.
Colonic ameboma accompanied by amebic liver abscess may be misdiagnosed as metastatic colon cancer. A high index of suspicion is essential for diagnosis when dealing with colonic masses and liver lesions, especially in the tropics.
|How to cite this article:|
Fernandes H, D'Souza CR, Swethadri G K, Ramesh Naik C N. Ameboma of the colon with amebic liver abscess mimicking metastatic colon cancer.Indian J Pathol Microbiol 2009;52:228-230
|How to cite this URL:|
Fernandes H, D'Souza CR, Swethadri G K, Ramesh Naik C N. Ameboma of the colon with amebic liver abscess mimicking metastatic colon cancer. Indian J Pathol Microbiol [serial online] 2009 [cited 2019 Oct 20 ];52:228-230
Available from: http://www.ijpmonline.org/text.asp?2009/52/2/228/48927
Amebiasis caused by Entamoeba histolytica is the most significant gastrointestinal parasitic infection in developing countries like India. Presentation ranges from diarrhea to dysentery and liver abscess. Years after the last attack of dysentery, a localized infection of the colon may form a segmental mass called ameboma. However, colonic ameboma has become rare even in endemic areas because of the availability of effective therapy. When it is found in association with amebic liver abscess, it can mimic metastatic colon cancer. We report a case with two lesions in the colon and an abscess in the liver.
A 59-year-old man was admitted to a peripheral hospital with a complaint of abdominal pain of 3 weeks duration. He was on treatment for diabetes mellitus. Abdominal examination revealed mild tenderness in the right ileac fossa. The liver was palpable 1 inch below the right costal margin. Laboratory results showed hemoglobin 11.2gm%, total leukocyte count 17,000/cumm and an erythrocyte sedimentation rate of 155mm at the end of the first hour. Liver function tests were normal except for alkaline phosphatase 205IU/mL (normal up to 170IU/mL). A peripheral smear study revealed anemia with eosinophilia. Abdominal ultrasound demonstrated thickening of the large bowel measuring 7cm in the region of ascending colon and hepatic flexure. Colonoscopy revealed an ulcerative growth from the cecal pole to the hepatic flexure. Serum carcinoembryonic antigen was 5.45ng/mL (normal 0-3.4ng/mL). A computed tomography (CT) scan of the abdomen demonstrated concentric wall thickening involving the ascending colon with pericolic fat stranding and pericolonic lymph nodes [Figure 1]. A cystic lesion measuring 4cm was seen in the right lobe of the liver. Biopsy from the colonic growth revealed inflammatory cells and necrosis.
He was referred to this hospital for surgical treatment with a provisional diagnosis of carcinoma of the colon. Peroperatively, cecal mass was identified. However, suspected secondaries were not seen on the surface of the liver. A right radical hemicolectomy with end-to-end anastomosis between the ileum and the transverse colon was performed. Recovery was uneventful. On cutting open the specimen, a large ulcerative growth in the caecum measuring about 8cm in diameter [Figure 2] was seen. The ulcer had overhanging edges, necrotic floor and indurated base. The cut surface of the ulcer showed necrotic exudate extending into the serosa and into the pericolic fat, with fibrosis of the adjacent bowel wall. Another ulcer measuring 4cm in diameter with similar features was seen in the ascending colon. Nine lymph nodes were identified in the pericolic fat.
Microscopic sections studied from both the ulcerative lesions revealed dirty necrosis, neutrophils, lymphocytes, eosinophils and granulation tissue [Figure 3]. In the dirty necrosis, scattered trophozoites of E. histolytica were seen [Figure 4]. Dense inflammatory infiltrate was seen in the submucosa, muscularis propria and serosa. The pericolic fat also showed inflammation and fibrosis. Periodic acid-Schiff (PAS) staining demonstrated bright pink trophozoites [Figure 5]. All the lymph nodes showed reactive changes.
Treatment was commenced on Metronidazole for 2 weeks followed by diloxamide furoate for an additional 2 weeks. The liver lesion was found to have resolved after 8 weeks on a subsequent abdominal ultrasound examination.
Amebiasis constitutes an important global problem, especially in the tropical and subtropical regions.  It primarily affects the colon but the liver is the most common extraintestinal organ involved. The presentation of intestinal amebiasis ranges from asymptomatic carrier state, colitis, through abscess formation to perforation. The parasite has been shown to be carried to the liver from the large bowel via the portal venous system.  Trophozoites of E. histolytica are responsible for the invasive disease. Intestinal invasion results in flask-shaped ulcers. Rarely, patients with long-standing or partially treated infection develop tumorous, exophytic, cicatricial and inflammatory masses known as "amebomas" or amebic granulomas.  It has been estimated that of all the cases with amebiasis, ameboma formation occurs in only about 1.5% of the patients.  The tissue necrosis in amebic colitis is replaced by extensive inflammatory reaction and psuedotumor formation, possibly because of secondary bacterial infection. Amebomas are usually solitary but can be multiple. Men between the ages of 20 and 60 years are usually affected. In decreasing order of frequency, lesions develop in the cecum, the appendix and the rectosigmoid region. Other sites include the hepatic flexure, the transverse colon and the splenic flexure.
Amebomas may cause obstructive symptoms. Alternating diarrhea and constipation, weight loss and low-grade fever may be seen. In endemic areas, cramping lower abdominal pain and a palpable mass suggest diagnosis. The differential diagnosis includes Crohn's disease and appendiceal abscesses in younger individuals and colon cancer and diverticulitis in the elderly.  Endoscopic evaluation yields a definitive diagnosis in about 60% of the cases. Biopsy specimens may be required to distinguish it from carcinoma or a large adenoma. Finding the trophozoites in the biopsy specimens may be difficult due to extensive cytolysis, especially in clinically unsuspected cases.  Trophozoites are better recognized after PAS staining. 
Because ameboma is a rare condition, it is usually discovered only at laparotomy.  Only a few cases of colonic amebomas have been reported where the diagnosis was made on colonoscopic biopsy and successfully treated with pharmacotherapy.  Metronidazole remains the mainstay of treatment for amebiasis.  Surgery is rarely required and is indicated only in cases of diagnostic uncertainty or if any complication occurs. 
Colonic ameboma accompanied by amebic liver abscess may be misdiagnosed as metastatic carcinoma of the colon.  Colonic involvement is common in patients with amebic liver abscess but most patients do not suffer from diarrhea, possibly because of the very limited extent of the pathology, which is confined to the right side of the colon.  More importantly, in regions where amoebic liver abscess is common, the reverse may happen and cancer of the colon or tuberculosis may be confused with ameboma, especially in patients with concurrent amebic liver abscess and its clinical signs and symptoms of high fever, local pain and tenderness.  Although imaging modalities like ultrasound and CT scan can differentiate secondaries from liver abscess, the clinical presentation in this patient allowed the disease to masquerade as carcinoma of the colon with secondaries in the liver. Amebic liver abscess responds well to pharmacotherapy and usually disappears within a few weeks after the treatment. , Treatment is with metronidazole or tinidazole and, to prevent continued intraluminal infection, diloxanide furoate or parvomycin.
On reviewing the case, we found that a primary diagnosis of amebiasis would have resulted in medical management with minimal morbidity. Therefore, especially in the topics, it is reiterated that keeping amebiasis in mind in colonic and liver lesions will definitely be useful.
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