Pseudoinvasion appearing as a deeply invasive malignant colorectal polyp.

A 50-year-old man with alcoholic liver cirrhosis and a Model for End-Stage Liver Disease score of 15 underwent colonoscopy as part of his evaluation and screening for liver transplantation. A malignant-appearing 20-mm sessile polyp with an ulcerated surface, Paris IIa/III, was seen in a tight area of the sigmoid. Owing to notable contractions, the polyp prolapsed into the lumen. The polyp surface, assessed with high-definition near-focus white-light and narrow-band imaging (CF-HQ190, Olympus Corp, Center Valley, Pa), demonstrated a Sano IIIb and Kudo Vn pattern for the ulcer and Sano II for the sharply demarcated margins, suggestive of deep submucosal invasion (A). Because the patient was considered a poor candidate for colectomy, the lesion was lifted with 10 mL saline–methylene blue and removed en bloc with a 2.5-cm stiff snare (Snaremaster, Olympus Corp, Center Valley, Pa) to obtain histologic examination (B). Surprisingly, histologic examination revealed a low-grade dysplastic tubulovillous adenoma with pseudoinvasion, probably representing ulceration from polyp prolapse. Although the architecture was disrupted, the epithelium appeared entrapped in fibrous stroma without evidence of true invasion (C, D, hematoxylin and eosin stain, orig. mag. ×20). Desmoplasia was not identified. Endoscopic assessment may occasionally be incorrect when mechanically caused pseudoinvasion appears as an invasive surface pattern. En bloc resection for histologic evaluation should then be considered.