Between 6 and 20 percent of the population develop acute appendicitis during their lifetime. By definition, the pathologic finding in acute appendicitis is mucosal disruption with invasive infection and inflammation. The invasive organisms, consistent with normal stool flora, include E. Coli, Klebsiella, and Enterobacter. However, not all luminal obstructions cause acute appendicitis and certainly not all acute appendicitis is caused by obstruction. Following obstruction the appendix continues to secrete into a closed lumen causing increased luminal pressures with eventual venous congestion and infarction along the watershed region.
Eventual perforation is preceded by mucosal ulceration and transmural necrosis.
Abscess formation or peritonitis may ensue. Children less than 5 years of age and adults over the age of 50 will typically present later in the disease process and frequently with vague signs and symptoms. This pain is regulated by autonomic visceral pain fibers. Nearly 95 percent of patients will experience a pain similar to this described. Anorexia is present in 90 percent of patient's at this stage.