What causes appendicitis?

Causes of Appendicitis

Appendicitis is primarily caused by obstruction of the appendiceal lumen, most commonly due to fecaliths, lymphoid hyperplasia, or parasites, which leads to increased intraluminal pressure, venous congestion, and subsequent mucosal ischemia. 1

Pathophysiological Process

• The natural progression of appendicitis follows three stages: normal appendix, uncomplicated acute appendicitis, and complicated appendicitis (gangrenous or perforated) 1
• Obstruction of the appendiceal lumen leads to increased intraluminal pressure, which compromises venous return and causes mucosal ischemia 1, 2
• As inflammation progresses, bacterial overgrowth occurs, leading to transmural inflammation, ischemia, and potential perforation 1
• Pain typically begins periumbilically and migrates to the right lower quadrant as the parietal peritoneum becomes inflamed 1

Common Causes of Obstruction

• Fecaliths (hardened fecal matter) are a primary cause of appendiceal lumen obstruction 1, 3, 4
• Lymphoid hyperplasia, often triggered by viral infections, can cause obstruction of the appendiceal lumen 3, 4
• The presence of an appendicolith (calcified fecal material) is strongly associated with progression to complicated disease 1
• Parasitic infections can obstruct the appendiceal lumen and trigger appendicitis 1, 3

Less Common Causes

• Tumors, including colonic adenocarcinoma, can cause obstruction of the appendiceal orifice, particularly in older patients 5, 3
• External compression from adhesive bands can create outflow obstruction leading to appendicitis 2
• Structural changes in elderly patients, including vascular sclerosis and muscular layers infiltrated with fat, create weakness and tendency toward early perforation 1

Risk Factors for Complicated Appendicitis

• Advanced age significantly increases risk of perforation, with elderly patients (>65 years) having perforation rates of 18-70% compared to 3-29% in younger patients 1
• Delayed presentation and diagnosis significantly increase perforation risk, with the median duration from symptom onset to definitive care in complicated cases being approximately 4 days 1
• Mortality increases dramatically with disease progression: less than 0.1% for non-gangrenous appendicitis, 0.6% for gangrenous appendicitis, and approximately 5% for perforated appendicitis 1

Epidemiological Considerations

• Appendicitis is the most common cause of intra-abdominal sepsis worldwide, accounting for 34.2% of cases 1
• The incidence in developed countries ranges from 5.7-50 patients per 100,000 inhabitants per year, with peak incidence between ages 10-30 years 1
• Lifetime risk varies geographically: 9% in the USA, 8% in Europe, and 2% in Africa 1
• After adolescence, the incidence decreases with increasing age, but elderly patients have significantly higher rates of complications 1