In the sixth week of the embryo, a cone-shaped blind sac appears on the edge of the mesenteric margin of the distal branch of the midgut, which is the primordium of the cecum and appendix. The tip of the blind sac gradually grows into the appendix. In the tenth week, the midgut in the umbilical cord returns to the abdominal cavity and begins to rotate counterclockwise. By birth, it has rotated a total of 270°, and the cecum and appendix originally in the lower left side rotate to the right iliac region. If the midgut does not rotate or rotates incompletely, the cecum and appendix are located in the original position or somewhere along the way of the translocation in the left lower abdomen, forming an ectopic appendix. Another reason for an ectopic appendix is that the midgut is not completely fixed, causing the cecum and appendix to be in a free state. There are several types of ectopic appendix: ① Non-inversion deformity: the small intestine is located on the right, the colon is located on the left, and the cecum and appendix are ectopically located in the left lower abdomen; ② Incomplete rotation: the cecum and appendix are ectopically located somewhere along the way, such as the left upper abdomen or under the liver, the latter is also called a high appendix; ③ Incomplete fixation of the ascending colon: incomplete fixation of the cecum and ascending colon causes variable appendix position; ④ Reverse inversion: extremely rare. The midgut rotates in a clockwise direction, so that the small intestine is entirely on the left, the ascending colon is on the right, and in a few cases, the cecum and appendix are in the middle. Another situation that can be seen in ectopic appendix is that the appendix is located outside the peritoneum behind the cecum. This is because the appendix turns to the peritoneum behind the cecum during the elongation and descent of the cecum.