Perforation. The major complication of amebiasis in the alimentary tract is penetration of one or more ulcers through the serosa, causing a thoracic, subphrenic or pericolic abscess, or peritonitis with or without internal or external fistula (Figs. 1.43, 1.44, 1.45, 1.46). The radiologist must remember that a pericolic abscess may manifest itself only as rigidity and distortion of the bowel wall; it should be suspected when there is a palpable mass clinically but none can be demonstrated radiologically. The appendix may be involved, and an appendiceal abscess may occasionally be amebic in origin. Ischiorectal or perineal amebic abscesses are not unusual and often have associated perianal and perineal cutaneous ulceration.

Appendicitis - Amebic Typhloappendicitis. In the overwhelming majority of the cases, the coexistent involvement of other segments of the colon by amebic colitiis allows the observer to suspect the parasitic etiology.

Colonic Stenosis Following Amebiasis. Following amebicidal medical treatment, the colonic morphology undergoes "restitutio ad integrum" even in the most extensive and severe cases: some investigators say only .1% of these patients present with a sequel of stenosis. However, Martinez et al found a persistent focal stenosis in 29% of metronidazole-treated patients who were examined several months following successful therapy. Retrospectively, a deep necrotic ulcerated area was the most common finding during the acute phase of the disease. Prado et al reported stenosis in 2 out of eight patients. It is therefore recommended that a barium enema be performed after completion of treatment to assess for possible sequelae.

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Fig. 1.43 Peritonitis secondary to perforation of amebic ulcers through the serosa of the bowel in a Mexican adult. (A) AP supine view of the abdomen reveals multiple dilated loops of small and large bowel primarily in the midabdomen. Note the separation of the bowel loops caused by thickening of the intestinal wall and mesentery and irregular thumbprinted contour of several loops from mucosal edema. Note also the slightly elevated right hemidiaphragm and large liver in this patient with hepatic amebic abscess as well as amebic colitis. (B) Upright view of the abdomen showing numerous air-fluid levels within both small and large bowel from severe paralytic ileus. There is also moderate ascites. (C) Lateral decubitus view showing marked distention of the colon and small bowel beneath the peritoneal surface. Fluid levels are seen in the more dependent loops. (A, B and C courtesy of Dr. Jorge Ceballos-Labat, Mexico City.) (D) Gross specimen of a severely ulcerated, fragile colon with numerous large perforations (white areas in center) in another patient with fulminating amebic colitis and fatal peritonitis.

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Fig. 1.44 Amebic peritonitis in a child from San Salvador. Perforation of amebic ulcers through the colonic serosa led to fatal peritonitis manifest by generalized dilatation of small and large intestine and bowel wall thickening in several areas on AP supine (A) and erect (B) radiographs of the abdomen. Multiple fluid levels are present, primarily in the small bowel, on the erect view. The child also had ascariasis, with suggestion of at least one Ascaris (black arrow) seen in a dilated small bowel loop on the supine view (A). (C) In an African patient, marked leakage of barium from perforated amebic ulcers in the colon has led to huge collections of barium in both subphrenic spaces, especially on the right. This explains how subphrenic abscesses can develop following colonic perforation in patients with fulminant ulcerative amebic colitis. Multiple deep ulcers and areas of thumbprinting are seen in the partially filled descending colon on this ill-advised barium enema study.