There are four main pathological types of acute appendicitis. The first is acute simple appendicitis, where symptoms are relatively mild, characterized only by small ulcers and bleeding spots on the mucosal surface. The second is acute suppurative appendicitis, with more severe symptoms including serosal congestion and purulent exudation. The third is gangrenous and perforating appendicitis, which progresses from suppurative appendicitis causing necrosis and perforation of the appendix wall, potentially leading to acute peritonitis. The fourth type is periappendiceal abscess, which results from the suppurative and gangrenous progression of acute appendicitis, with the greater omentum encapsulating the appendix, forming a severe mass or a periappendiceal abscess.