Later, there is loss of haustration, chiefly in the descending and sigmoid colon (Figs. 2.31-2.34). Although any part of the bowel may be affected, in schistosomiasis mansoni the changes will be most marked in the distribution of the inferior mesenteric artery.

Where there has been a heavier infection and chronic exposure, there may be multiple granulomatous polyps, usually 1-2 cm in diameter, especially in the rectum, sigmoid and descending colon (Figs. 2.31, 2.32). The polyps begin as submucosal granulomas which lift the overlying mucosa and acquire a short stalk. They are very friable and vascular and bleed easily. They can become quite extensive and coalesce into a large hemorrhagic granuloma from which all the normal mucosa has been lost (Figs. 2.33, 2.34). These masses may become so large that there is obstruction or intussusception. Rectal prolapse can occur. Such lesions simulate carcinoma.

Polyp formation varies in different countries; they are not uncommon in Egypt, Arabia and other parts of Africa where S. mansoni infections predominate and are particularly common where there are combined S. mansoni and S. haematobium infections,but less frequent in S. mansoni infections alone. In the Western Hemisphere, colonic polyps are uncommon; in fact, radiologically detectable schistosomal colonic disease is rather uncommon except in severely infected individuals, in whom the most common finding is a stenosing granulomatous process with extensive pericolonic infiltration resembling granulomatous colitis.

Strictures may develop (Figs. 2.33, 2.34) and can be mistaken for carcinoma or Crohn's disease. Calcification in the eggs may be seen in the bowel and surrounding tissues (Figs. 2.35). It is best demonstrated by CT, but often can be seen on plain radiography, usually in the left side of the abdomen. As described in S. haematobium, it will have a very variable appearance,depending on the distention of the bowel. It can be spotty, laminar, corrugated, or amorphous. Near the rectum, the inflamed hypertrophic rectal mucosa may show a converging pattern of calcification towards the anus. Although many patients with colonic schistosomiasis will have diarrhea and bleeding, there is no close correlation between the number of calcified eggs, and the number and size of the polyps or the extent of colitis. Unlike adenomatous polyps, those from schistosomiasis are inflammatory and the majority will resolve after proper treatment. Unfortunately, the pericolonic fibrosis does not improve significantly with any therapy.

There are some parts of the world where schistosomal colonic polyps are very uncommon, e.g. in South America, although the egg count does not differ significantly from those countries in which colonic polyps are found more frequently. The reason for this is not fully understood.

Pericolonic schistosomal abscesses or pelvic granulomas may be large enough to compress the pelvic colon and displace it laterally and anteriorly. Large, solitary bilharziomas (schistosomal granulomatous masses) may occur, either in the bowel wall or mesentery, and can be mistaken for carcinoma.

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Fig. 2.31 A-H. Schistosomal polyposis in the colon and rectum. A Multiple polyps throughout the rectosigmoid colon, which was displaced out of the pelvis by a large pericolic bilharzial (schistosomal) abscess. There is mural spiculation, loss of haustration and spasm in the descending colon, with scattered strictures. There were S. mansoni eggs, blood, and pus in the stools. The patient was a 20-year-old Egyptian male complaining of bloody diarrhea, fatigue, and abdominal swellings. He had hepatosplenomegaly and anemia. (Courtesy of Dr. Hafez Hassan, Cairo) B Schistosomal polyposis (arrows) extending from the rectum to the transverse colon in a 42-year-old Egyptian (air-barium enema). C A 22-year-old Egyptian patient with marked schistosomal polyposis (arrows) in the rectum and sigmoid (air-barium contrast enema). (C, D Courtesy of Dr. N.A. El Masry, Cairo) D Extensive granulomas and polyposis of the sigmoid colon and rectum in a Brazilian patient with schistosomiasis mansoni. (Courtesy of Dr. J. Phillips et al. and Radiology, 1975) E, F A barium enema on a 16-year-old Puerto Rican girl who had a 6-year history of recurrent diarrhea and abdominal pain. There is a polypoid mass arising from the left lateral rectal wall in the frontal view (E), more clearly seen in the post evacuation film (F). (Courtesy of Dr. J. Medina et al. and Radiology, 1965) G Multiple areas of irregular narrowing, mucosal ulceration, spiculation, and granulomatous polyps, with a length of intense spasm in the mid-descending colon. The proximal colon is more normal. (Courtesy of Dr. John Ebersole, Lancaster) H Tubular narrowing of the entire rectum, sigmoid, and descending colon with numerous large (2 cm) polyps, with some areas of spasm, due to schistosomiasis mansoni in an Egyptian patient. (Courtesy of Prof. Kassem, Cairo).

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Fig. 2.32 A-E. Colonic and rectal polyps are ususally multiple and associated with a marked inflammatory reaction. A The hemicolectomy from an Egyptian patient with combined S. haematobium and S. mansoni infections. A large bilharzioma is surrounding the rectosigmoid colon and displacing it arterioirly and upwards. There are several polyps. There were about 23,000 S. mansoni eggs and 1500 S. haematobium eggs per gram of tissue, with numerous S. mansoni adult schistosomes in the irregular fibrous masses in the colonic serosa and in the bilharzioma. There were similar but less severe serosal changes throughout the remainder of the colon and small intestine. Clinically the mass was thought to be malignant. AFIP 76-2329. B Multiple polyps in the colon of 20-year-old Egyptian male with schistosomiasis mansoni. (Surgically resected: courtesy of Dr. Jerome H. Smith, Tucson) C A large inflammatory polyp on a short stalk in the sigmoid colon of a 10-year-old Egyptian boy. The polyp contained numerous S. haematobium eggs and a few S. mansoni eggs. There is a much smaller sessile polyp (lower right). There is a geographic variation in the frequency of polyps: they are not uncommon in Egypt and elsewhere in Africa, particularly in combined infections. They are not so frequent in Brazilians with S. mansoni infection. Polyps are also found in schistosomiasis japonica. D Transverse sections of the colon of an 18-year-old Egyptian male with combined S. mansoni and S. haematobium infections. There are multiple polyps almost filling the lumen and the colonic wall is very fibrotic and thickened. (Courtesy of A.W. Cheever) E Schistosomiasis mansoni causing thickening of the colonic wall, with narrowing and rigidity of the pelvic colon; the normal haustral pattern has been lost and there are multiple polypoid lesions in the rectum and sigmoid colon. There was also a large pericolic mass of fibrofatty granulation tissue displacing the bowel. AFIP 68-1095.

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Fig. 2.33 A-E. Schistosomiasis mansoni can cause marked granulomatous thickening of the bowel wall and, eventually, strictures. A Transverse sections of a stenosed segment of bowel from an 18-year-old Egyptian male. Elsewhere in the colon there were multiple polyps. This tissue contained 111,000 S. mansoni and 1500 S. haematobium eggs per gram, and was almost entirely inactive when removed. B Peritoneography combined with a double barium-air contrast study of the colon shows marked thickening of the wall of the distal colon (arrows) in a patient with S. mansoni. (Courtesy of Dr. Morton Meyers, New York) C Histological section through the colon of a different patient with chronic schistosomiasis mansoni showing an inflammatory reaction in the mucosa and many calcified schistosome eggs in the submucosa: there is marked collagen and fibrous tissue formation, which results in narrowing of the bowel lumen and eventually stricture or stenosis. AFIP 68-4761. D This barium enema shows stenosis of the rectum and a stricture in the midsigmoid colon. Throughout the rectosigmoid there is loss of haustral markings and the bowel has become tubular and rigid. Proctoscopy confirmed the rectal stricture, which was thought to be malignant until the biopsy showed edema, granulomas, and multiple schistosome eggs. AFIP 68-9019-15. E CT scanning can show calcification in the wall of the colon. This is the nonenhanced CT scan of an 86-year-old Japanese man showing calcification in the wall of the colon (arrows). S. japonica were found in his stool.