Gangrenous appendicitis. Light micrograph through a section of an appendix showing gangrenous appendicitis. In appendicitis, the epithelial lining of the appendix becomes ulcerated and secretes an inflammatory exudate (thick fluid). As the disease progresses, the inflammation spreads until until the exudate is present on the external surface (peritoneum) of the appendix. This causes peritonitis (inflammation of the peritoneum) and increases susceptibility to opportunistic infections. Here, necrosis (tissue death) has arisen as a result of infection (gangrene, white spots at bottom and lower left). Pus from the infection is also seen (top right).