## Histopathological Progression of Acute Appendicitis **Key Point:** Acute appendicitis progresses through a predictable sequence of histological changes, beginning with neutrophilic infiltration and culminating in potential perforation. ### Sequential Changes 1. **Neutrophilic infiltration** (earliest change) - Begins in the lamina propria and submucosa - Triggered by bacterial invasion or obstruction - Occurs within the first 6–12 hours 2. **Mucosal ulceration** - Follows neutrophilic infiltration - Results from loss of epithelial integrity - Allows deeper bacterial invasion 3. **Transmural inflammation** - Extends through all layers of the appendiceal wall - Involves the serosa and peritoneum - Leads to peritoneal irritation and systemic inflammation 4. **Perforation** - Occurs at the antimesenteric border (weakest point) - Results from full-thickness necrosis - Typically happens after 48–72 hours if untreated **High-Yield:** This sequence is a classic teaching point and frequently tested in NEET PG. Understanding the timeline helps explain clinical presentation and urgency of intervention. **Mnemonic:** **NITP** — **N**eutrophilic infiltration → **I**nflammation (transmural) → **T**ransmural changes → **P**erforation (Note: ulceration occurs early, between N and I) ### Clinical Correlation - **Early appendicitis (0–24 hrs):** Neutrophilic infiltration only; minimal symptoms - **Acute appendicitis (24–48 hrs):** Transmural involvement; classic pain migration and localization - **Perforated appendicitis (>48 hrs):** Full-thickness necrosis; peritonitis develops 
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