The main complications of acute appendicitis include: First, purulent peritonitis, due to the appendix becoming purulent and leading to perforation, pus flows into the abdominal cavity, causing diffuse peritonitis; Second, abdominal abscess, purulent appendicitis that is not treated surgically forms a capsule around the appendix, encapsulating it, and a lump can be felt on the abdominal surface; Third, internal-external fistula, if the abscess around the appendix is not drained in time, it can break through to the intestinal abdominal wall, forming a fistula.