Teaching Case

A 49-year-old male patient presented with history of per rectal bleeding and vague abdominal pain since one month. The abdominal examination revealed moderate left lower-quadrant tenderness. The per rectal examination revealed a hard mass which necessitated radiological examinations. Later endoscopy was performed, followed by a biopsy, which confirmed the diagnosis.

A triphasic CT scan of abdomen and pelvis was performed after positive oral and rectal contrast administration on 258 slice multidetector dual CT scanner machine, followed by a plain MRI of pelvis on 3T scanner. Contrast CT images showed asymmetrical, inhomogenously enhancing rectal wall thickening and a non-enhancing polypoidal soft-tissue density lesion along right lateral aspect of rectum projecting intraluminally. T2-weighted fat suppressed images showed abnormal hyperintense wall-thickening of upper and mid rectum of about 10-12 mm and an intraluminal hypointense polypoidal lesion of about 20x15 mm in axial plane. Mild fat stranding was seen in mesorectal fascia. A small perirectal node was also present. Mild presacral fluid was seen. There were no signs of intestinal obstruction. Mild thickening of sigmoid and ascending colon was seen. The other abdominal organs were normal. The diffusion-weighted images did not reveal any abnormal restricted diffusion within the lesion and the lymph node.

The initial colonoscopy images showed ulcerated lesions with sloughing in mid and lower rectum. The biopsy from the rectal lesion showed changes of amoebic proctitis with ulceration (Section revealed rectal mucosa with ulceration and a few trophozoites of E. histolytica - PAS Positive).

Post-treatment follow-up colonoscopy showed significant regression in the rectal lesion.

Follow-up CT and MRI were not performed.

The term amoebiasis is used clinically to denote all conditions which are produced in the human host by infection with entamoeba histolytica. Ameboma of the large bowel is a rare condition, which is difficult to differentiate from colorectal carcinoma. Rectal ameboma is an uncommon complication of intestinal amoebiasis, occurring in 1.5 percent of all cases [1]. E. histolytica is a major cause of dysentery in developing countries. An estimated 20% of world population harbor E. histolytica, but only a small number of patients develop invasive amoebiasis [2]. The symptoms include recurrent diarrhoea, lower gastrointestinal bleeding, lower abdominal pain, weight loss, low-grade fever, abdominal mass and even intestinal obstruction [3].

Our patient was from a developing country where the prevalence of amoebiasis is common.
Radiological imaging was needed in our patient to know the morphology and extent of the disease, adenopathy, presence of ascites and involvement of other organs.

Both MRI and CT show marked circumferential mural rectal wall thickening and mildly inhomogeneous contrast wall enhancement. Inflammatory stranding of the mesorectal fat and enlarged perirectal lymph nodes can be seen. Often, with invasive amoebiasis both endoscopic and cross-sectional imaging findings suggest proctitis, ulcers or masses, and differentiation from neoplastic processes is not always possible [4,5]. The radiological findings of our case mimicked carcinoma which necessitated endoscopy and biopsy [6,7]. Diagnosis of amoebiasis is rapidly made by testing for circulating antibodies to E. histolytica, although serologic markers may be elevated for years after infection. Stool analysis can be negative even in active infection, stool antigen assay is more specific.  

TREATMENT:
Our patient was placed on three weeks of oral metronidazol. A repeat colonoscopy after three weeks showed significant regression.

TEACHING POINTS:
Consideration of this diagnosis is warranted in any patient with a rectal mass, symptoms of intestinal amoebiasis and travel history to an endemic area.
Good team work allows for proper diagnosis and treatment avoiding unnecessary surgical interventions.

Written informed patient consent for publication has been obtained.