Ectopic Enterobius vermicularis

<i>Enterobius vermicularis</i> (the pinworm) commonly infests the lumen of the intestine but on rare occasions has been found in the wall or in the tissues outside the gastrointestinal tract. Three such patients have been encountered in whom <i>Enterobius vermicularis</i> was found in the wall of the colon, in the retrocaecal tissues, and on the peritoneum. The pathological lesions and their relationship to the clinical features are discussed. A brief review of the literature is given. It is concluded that <i>Enterobius vermicularis</i> can only penetrate the wall of the gastrointestinal tract if this is diseased. Once in the tissues the worms can cause an inflammatory reaction simulating carcinoma and Crohn9s disease, and, by perforation of the intestine, cause a generalized peritonitis.