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Gastrointestinal: Rectal polyp associated with schistosomiasisA Japanese man, aged 64 years, was investigated by colonoscopy because of a positive fecal occult blood test. Colonoscopy revealed a sessile polyp, about 2 cm in diameter, in the rectum. The appearance of the polyp after spraying the region with indigo carmine is shown in Fig. 1. As the polyp was thought to be an adenoma, the polyp was removed by endoscopic mucosal resection. Histological evaluation revealed a hyperplastic polyp and calcified Schistosoma eggs in the submucosa (Fig. 2).Schistosomes are tropical parasites that are thought to infect at least 200 million people worldwide. The major human parasites are Schistosoma hematobium , S. mansoni and S. japonicum . S. hematobium is endemic in several countries in Africa while S. mansoni is endemic in Africa and Central and South America. S. japonicum is largely restricted to East Asia but is now rare in Japan. The location of adult worms in the human host is partly determined by parasite species. For example, the preferred site for S. hematobium is vesical veins while the preferred sites for S. mansoni and S. japonica are the superior and inferior mesenteric veins. Adult worms of S. japonicum survive for approximately 5 years and produce up to 3000 eggs per day. At least half of these eggs pass through the intestinal wall and are discharged in feces. The remainder lodge in the intestinal wall or go back to the liver via the portal vein. These eggs elicit a chronic inflammatory response that includes granulomas and large numbers of eosinophils. Common clinical manifestations include hepatomegaly and various manifestations of portal hypertension. It is unclear whether intestinal schistosomiasis predisposes to colorectal polyps but S. japonica eggs were found in the base of the polyp in the above case.

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