What Causes Appendicitis
Appendicitis develops primarily from obstruction of the appendiceal lumen by fecaliths (hardened stool) or parasites, leading to increased intraluminal pressure, mucosal ischemia, and subsequent bacterial invasion. 1
Primary Pathophysiological Mechanism
The fundamental cause follows a well-established sequence:
- Luminal obstruction is the initiating event, most commonly caused by fecaliths (hardened fecal matter) or parasites that block the narrow appendiceal opening 1
- This obstruction creates a closed-loop system where continued mucus secretion increases intraluminal pressure 1
- Rising pressure compromises venous and lymphatic drainage, causing mucosal ischemia and edema 1
- Ischemic mucosa becomes vulnerable to bacterial invasion from normal intestinal flora, leading to inflammation and potential perforation 1
Contributing Factors and Disease Progression
The natural history follows three distinct stages:
- Stage 1: Normal appendix 1
- Stage 2: Uncomplicated acute appendicitis (approximately two-thirds of cases) 1
- Stage 3: Complicated appendicitis with gangrene or perforation (perforation rates 16-40%) 1
Structural and Age-Related Factors
- Appendicoliths (calcified fecal concretions) are strongly associated with progression to complicated disease and perforation 1
- Elderly patients develop vascular sclerosis of the appendix with muscular layers infiltrated by fat, creating structural weakness and tendency toward early perforation 1
- Lymphoid hyperplasia may contribute to obstruction, particularly in younger patients, though this represents only a small percentage of cases that progress to complete occlusion 2
Clinical Presentation Pattern
The characteristic pain migration reflects the underlying pathophysiology:
- Pain typically begins periumbilically due to visceral innervation of the inflamed appendix 1
- Pain then migrates to the right lower quadrant as the parietal peritoneum becomes inflamed 1
- Additional findings that increase likelihood include fever, positive psoas sign, and migratory pain to the right lower quadrant 3
Risk Factors for Complicated Disease
Several factors significantly increase perforation risk:
- Advanced age (>65 years) dramatically increases perforation rates to 18-70% compared to 3-29% in younger patients 1
- Delayed presentation with median duration of approximately 4 days from symptom onset to care in complicated cases 1
- Mortality risk increases threefold with each decade of age beyond 65 years 1
Geographic and Epidemiologic Considerations
- Appendicitis accounts for 34.2% of all intra-abdominal infections worldwide, making it the most common cause of intra-abdominal sepsis 1
- In resource-limited settings, parasitic infections (Entamoeba, Ascaris, Trichuris trichiura, Enterobius vermicularis, Salmonella Typhi) can mimic or cause appendicitis 3
- Lifetime risk varies geographically: 9% in USA, 8% in Europe, 2% in Africa 1
Common Pitfalls
- Atypical presentations are common, particularly in elderly patients and children, often resulting in delayed diagnosis 3
- The presence of vomiting before pain onset makes appendicitis unlikely 3
- Not all appendicitis progresses to perforation; some cases of simple appendicitis may be self-limiting, though this remains controversial 4