A case of inverted serrated polyp that mimics a submucosal tumor

Abstract

A 68-year-old woman underwent colonoscopy because of abdominal discomfort and changing of bowel movements for half a year. A submucosal protruded lesion, 4 mm × 5 mm, with smooth and intact cover mucosa was found at the rectum 4 cm from the anal margin (A). EUS with a miniprobe revealed a heterogenously hyperechoic lesion with clear margins (B, yellow arrow). The lesion was mainly located between the mucosal and submucosal layers, with a maximum size 3.8 × 4.5 mm in diameter. A thin layer of submucosal structure existed beneath the lesion (B, yellow arrow). The physical examination, laboratory examinations, and abdominal and pelvic CT revealed no remarkable findings. Endoscopic submucosal dissection (ESD) was recommended, and the lesion was removed en bloc. Pathologic examination revealed serrated intestinal mucosa within the muscularis mucosal layer, which was consistent with inverted serrated polyps. The lesion also demonstrated the characteristics of low-grade intraepithelial neoplasia. Genetic testing indicated the existence of a BRAF gene mutation. Histopathologic analysis showed the serrated tubular features (C, black arrows) of this lesion and a small area of defective muscularis mucosae (D, yellow box) on top of the protrusion.