A 22-year-old male presents with acute right lower quadrant pain, fever, and anorexia. On examination, tenderness is maximal at McBurney's point. What is the most common cause of acute appendicitis?

Explanation

## Etiology of Acute Appendicitis **Key Point:** Lymphoid hyperplasia is the most common identifiable cause of acute appendicitis, accounting for approximately 50–60% of cases with a demonstrable pathological cause. ### Pathophysiology of Lymphoid Hyperplasia Lymphoid tissue in the appendix undergoes reactive hyperplasia in response to: - Viral infections (adenovirus, rotavirus, measles) - Bacterial infections (Yersinia, Salmonella) - Immune stimulation from gastrointestinal pathogens This hyperplasia narrows the appendiceal lumen, leading to: 1. Increased intraluminal pressure 2. Mucosal ischemia 3. Bacterial invasion and inflammation 4. Progression to suppuration and perforation if untreated ### Comparison of Causes of Acute Appendicitis | Cause | Frequency | Age Group | Notes | |-------|-----------|-----------|-------| | **Lymphoid hyperplasia** | 50–60% | Children & young adults | Most common; often viral prodrome | | Fecal impaction | 20–30% | Older adults | More common in constipation | | Carcinoid tumor | <1% | Middle-aged | Rare; found incidentally | | Crohn's disease | <1% | Young adults | Associated with terminal ileitis | | Foreign body | Rare | Variable | Accidental ingestion | | Stricture | Rare | Variable | Post-inflammatory | **High-Yield:** Lymphoid hyperplasia is the leading cause in children and young adults (< 30 years), which is the typical demographic for acute appendicitis. In older patients (> 50 years), fecal impaction and neoplasia become relatively more common. **Clinical Pearl:** Most cases of acute appendicitis (40–50%) have no identifiable structural cause on histology — these are presumed to be due to functional obstruction or mucosal inflammation from viral agents that are not always detected. ### Why Lymphoid Hyperplasia Is the Answer Lymphoid hyperplasia is: - The most frequently demonstrated pathological cause - Strongly associated with recent viral illness - Reversible if appendicitis is treated early - More common in the pediatric and young adult population where appendicitis is most prevalent [cite:Sabiston Textbook of Surgery 21e Ch 51]