A 50-year-old woman presented with right lower-abdominal pain for more than 1 month. Colonoscopy revealed a 1.8-cm submucosal bulge near the appendiceal orifice (Figure A). Computed tomography, magnetic resonance imaging, and endoscopic ultrasound were suspicious for appendiceal mucocele. The patient declined laparoscopic or conventional surgical appendectomy, but agreed to endoscopic transcecal appendectomy (ETA) after multidisciplinary discussion. The procedure steps were as follows (Supplementary Video): the appendiceal lesion margin was marked using a woodpecker I-knife (multifunctional knife, Anrei); a full-thickness circumferential incision was made along the marks and the appendiceal orifice with the woodpecker knife (I- and O-knife); the root of the partially dissected appendix was retracted using a snare to adequately expose the incision line and continue dissection; the woodpecker knife (O-knife) was used to dissect the mesoappendix along the appendix, and mesentery vessels w

A 73-year-old woman with a history of appendectomy for acute appendicitis was diagnosed with a 20-mm laterally spreading tumor involving the appendiceal orifice site (Figure A). Although computed tomography scan revealed the whole image of the appendiceal stump, the tumor margin could not be confirmed endoscopically. Complete resection of the tumor using conventional endoscopic submucosal dissection procedure was difficult, and endoscopic excision, including full-thickness resection of the appendiceal stump, was performed.