Fig. 1.

 The conventional method was performed as follows. a An antegrade approach gives a vertical approach at the pyloric sphincter. To avoid the solid muscularis of the pyloric sphincter, the upward angle also leads to a vertical approach against the submucosal side of the dissected mucosa that may damage the resected specimen. After getting over the pyloric ring, a horizontal approach in the duodenal bulb is impossible because the dissected mucosa falls down to the duodenal side and the tip of the endoscope becomes unstable due to the high muscularis of the pyloric ring. b With a retroflexed approach, maneuverability is limited in the narrow space in the duodenal bulb. The vertical approach at the pyloric sphincter makes submucosal dissection difficult.