Endoscopic submucosal dissection of a squamous cell carcinoma in situ in the anal canal diagnosed by magnifying endoscopy with narrow-band imaging.

A 60-year-old female underwent screening colonoscopy. Narrow-band imaging (NBI) without magnification showed a 20-mm, well-demarcated brownish area located close to the dentate line of the anal canal. Conventional white-light imaging revealed an ill-defined, flat lesion with scattered reddish spots at the same site. Magnifying endoscopy with NBI (M-NBI) revealed abnormal microvessels with dilatation, tortuosity, caliber change and various shapes that were similar to the intrapapillary capillary loop patterns seen in esophageal squamous cell carcinoma in situ. Endoscopic submucosal dissection (ESD) was performed, and on histological examination, the resected specimen showed squamous cell carcinoma (SCC) in situ and clear surgical margins. Thus, NBI is an efficient method for detecting superficial SCC in the anal canal and M-NBI may be useful for determining the extent of the lesion. During screening colonoscopy, the anal region should be carefully observed using NBI, as early detection offers a greater opportunity for ESD which is a less invasive procedure.