Lymphoid tissue hyperplasia (60% of cases): most common cause in children and young adults
The lamina propria and submucosa of the appendix have an abundance of lymphoid follicles. Hyperplasia of these follicles may be physiological (e.g., during childhood and adolescence, when lymphoid tissue is developing and maturing) or pathological (e.g., secondary to an infectious or inflammatory process within the bowel).
Appendiceal fecalith (concretion of feces that develops in the appendix that can obstruct the appendiceal lumen) and fecal stasis (35% of cases): most common cause in adults
Obstruction leads to mucus buildup, increased intraluminal pressure, bacterial overgrowth, and inflammation, which can progress to ischemia, necrosis, and perforation.
Neoplasm (uncommon): more likely in patients > 50 years of age
