What causes appendicitis in people of all ages?

What Causes Appendicitis

Appendicitis results from obstruction of the appendiceal lumen, most commonly by fecaliths (hardened stool) or parasites, which leads to increased intraluminal pressure, mucosal ischemia, bacterial overgrowth, and subsequent inflammation. 1

Primary Pathophysiological Mechanism

The fundamental cause of appendicitis is luminal obstruction that triggers a cascade of pathological events 1:

• Fecaliths and parasites are the most common obstructing agents that block the narrow appendiceal opening 1
• Once obstructed, intraluminal pressure rises as mucus secretion continues 1
• Elevated pressure compromises blood flow, causing mucosal ischemia 1
• Ischemic tissue becomes vulnerable to bacterial invasion from normal intestinal flora 1
• This progression leads to inflammation, edema, and potentially perforation if untreated 1

Age-Related Anatomical Factors

In elderly patients (>65 years), specific anatomical changes increase vulnerability 2, 1:

• Vascular sclerosis develops in the appendix with aging, reducing blood supply 2, 1
• Narrowing of the lumen by fibrosis makes obstruction more likely 2
• Muscular layers become infiltrated with fat, creating structural weakness 2, 1
• These changes create a tendency toward early perforation (18-70% perforation rate vs. 3-29% in younger patients) 2, 1

Natural Disease Progression

The disease follows a predictable three-stage evolution 1:

1. Normal appendix → initial obstruction
2. Uncomplicated acute appendicitis → inflammation without perforation (represents approximately two-thirds of cases) 1
3. Complicated appendicitis → gangrenous changes, perforation, abscess formation, or diffuse peritonitis 1

Perforation rates vary from 16-40% overall, with higher frequencies in the very young (40-57%) and those older than 50 years (55-70%) 1

Clinical Presentation Pattern

The typical pain migration reflects the underlying pathophysiology 1:

• Pain begins periumbilically when visceral peritoneum is irritated by the distended appendix 1
• Pain migrates to the right lower quadrant as the parietal peritoneum becomes inflamed 1
• This classic pattern occurs because parietal peritoneum has somatic innervation providing precise localization 1

Critical Risk Factor: Appendicolith

The presence of an appendicolith (visible calcified fecalith on imaging) is the single most important predictor of disease progression 1, 3:

• Strongly associated with progression to complicated disease 1
• Significantly increases perforation risk 3
• Predicts treatment failure with antibiotic therapy 3

Common Pitfalls

The underlying cause remains poorly understood beyond the obstruction mechanism 4, 5. Despite decades of research, we lack complete understanding of why some patients develop self-limiting disease while others rapidly progress to perforation before reaching medical care 4. This suggests at least two distinct disease phenotypes—non-perforating (uncomplicated) and perforating (complicated) appendicitis—though the exact triggers differentiating these pathways remain unclear 5.

Delayed diagnosis significantly increases perforation risk, with median duration from symptom onset to definitive care in complicated cases being approximately 4 days 1. In elderly patients, diagnostic delays are particularly problematic due to atypical presentations and concurrent comorbidities 2.