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Differential Diagnosis

In parts of the world where bowel malignancy is rare and diverticulitis is uncommon, these two diseases seldom enter into the differential diagnosis. Helminthoma in its chronic stage, however, may closely simulate ameboma or a colonic carcinoma clinically and radiologically. It may be firm, irregular and non-tender to palpation and produce a mass partially encircling the bowel on barium enema examination, CT, or ultrasound. The intactness of the mucosa, with no evidence of ulceration or destruction, and the intramural location of the mass should help to distinguish helminthoma from carcinoma. Further, there may not be melena clinically, and there is often a history of a prior subacute inflammatory process in the area. Unfortunately, this combination of clinical and imaging findings, does not exclude ameboma, carcinoma or even tuberculosis.

Since helminthomas occur most commonly in the cecum and ascending colon, they are most frequently misdiagnosed in their acute phase as appendicitis or amebiasis, with abscess formation. The more gradual onset of symptoms, absence of periumbilical pain, and an elevated eosinophil count may help exclude appendicitis. When a normal appendix is seen radiologically, or by CT or ultrasound, and there is an intramural cecal mass, especially in patients with a lengthy clinical history, the possibility of helminthoma needs to be considered.

Amebiasis or ameboma may be recognized because there are usually other areas of amebic colitis, as well as the local contraction which usually occurs around the full width of the bowel.

Schistosomiasis can occasionally present as a solitary polypoid mass, which is characteristically intraluminal, usually in the rectum or sigmoid colon; careful search will nearly always demonstrate other areas of involved bowel, with mucosal edema, polyps, and thickening of the wall. Scanning may show calcified schistosome ova around the bowel, but these may be coincidental because patients with schistosomiasis can develop a helminthoma also.

As with many other tropical diseases, the radiologist needs to know the pattern of local diseases and have a high index of suspicion to suggest the right diagnosis. An element of good luck also helps.

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