Incidental Detection of Asymptomatic Colonic Anisakiasis During Surveillance Colonoscopy: A Case Report and Literature Review.

Anisakiasis is a parasitic infection caused by ingestion of raw or undercooked seafood containing Anisakis larvae. Although gastric involvement is common, colonic anisakiasis is rare and may be asymptomatic, making diagnosis difficult without endoscopic evaluation. We report a case of asymptomatic colonic anisakiasis incidentally detected during surveillance colonoscopy in a 53-year-old man 2 years after endoscopic submucosal dissection (ESD) for a sessile serrated lesion. The patient had consumed raw squid the evening before colonoscopy but had no abdominal symptoms. Bowel preparation was performed using an oral polyethylene glycol plus ascorbate solution. Colonoscopy revealed a worm-like parasite embedded in the ESD scar in the cecum. The larva was successfully removed using biopsy forceps without complications. Histopathological examination confirmed anisakiasis, showing chronic inflammatory changes with focal neutrophilic infiltration. A review of previously reported cases suggests that colonic anisakiasis occurs predominantly in the right colon and is more frequently asymptomatic than generally recognized. Symptomatic cases typically present with abdominal pain and may occasionally lead to complications such as intussusception, whereas asymptomatic cases are often detected incidentally during endoscopy. This case highlights that colonic anisakiasis can be completely asymptomatic and incidentally identified, even after standard bowel preparation. Awareness of this condition and careful dietary history-taking are important, particularly given the increasing global consumption of raw seafood, and endoscopic examination remains essential for accurate diagnosis and management.