A 50-year-old, asymptomatic man underwent scheduled screening colonoscopy. Because of his first-degree family history for colorectal cancer, he had previously undergone a colonoscopy 5 years before, but no mucosal alterations were found. A total colonoscopy was performed without difficulty under conscious sedation with midazolam 5 mg i.v., although mild pain occurred when the colonoscope passed through the sigmoid tract. Withdrawal of the endoscope also elicited pain in the sigmoid, where some mucosal folds appeared to be moderately enlarged. When the tract was more closely observed, a mobile nematode was discovered among the folds, showing extremely strong adherence to the mucosa (Fig. 1A). The worm was grasped and successfully removed with a forceps. In the adjacent mucosa, we observed some slight elevated nodules with apical depression (Fig. 1B). Histological examination of these lesions showed a marked infiltration of eosinophils in the colonic mucosa (Fig. 1C). The removed nematode was characterized as 18-mm long Anisakis simplex (Fig. 1D). The patient disclosed that he had eaten uncooked anchovies 5 days before. No symptoms occurred at 3-month follow up.
Figure 1 (A) A mobile nematode detected on the sigmoid mucosa. (B) Erosive lesions on the adjacent mucosa. (C) Histological examination of erosions showing infiltration of eosinophils. (D) Microscopic observation showing Anisakis simplex
Endoscopic diagnosis of Anisakis in the stomach and in the colon has been reported in symptomatic patients [1-3]. However, to our knowledge, only 4 cases of anisakiasis detection in the colon in asymptomatic subjects have previously been described [3]. We would suggest that the adjacent nodular mucosal alterations may represent the result of unsuccessful attempts of the same worm—or other similar ones, probably eliminated during bowel preparation—to fix on the mucosa.