## Most Common Site of GI Metaplasia **Key Point:** Barrett's esophagus (columnar metaplasia of the distal esophagus) is the most common and clinically significant metaplasia in the gastrointestinal tract. ### Pathophysiology of Barrett's Esophagus 1. **Chronic GERD** → repeated acid injury to distal esophageal mucosa 2. **Loss of stratified squamous epithelium** (normal esophageal lining) 3. **Replacement by columnar epithelium** with intestinal-type mucosa (metaplasia) 4. **Increased cancer risk** → 0.2–0.5% annual progression to adenocarcinoma ### Comparison of GI Metaplasias | Site | Trigger | Metaplastic Change | Clinical Significance | |------|---------|-------------------|----------------------| | **Distal esophagus** | Chronic GERD | Squamous → Columnar (intestinal) | **Most common; premalignant** | | Gastric cardia | Chronic atrophic gastritis | Gastric → Intestinal | Less common; associated with H. pylori | | Duodenum | Gastric metaplasia (rare) | Duodenal → Gastric | Rare; seen in peptic ulcer disease | | Rectosigmoid | Chronic irritation/schistosomiasis | Columnar → Squamous | Rare in developed countries | **High-Yield:** Barrett's esophagus affects 5–15% of GERD patients and is the only metaplasia in the GI tract with established premalignant potential requiring surveillance endoscopy. **Clinical Pearl:** The diagnosis requires endoscopic visualization of columnar epithelium above the gastroesophageal junction PLUS histologic confirmation of intestinal metaplasia (presence of goblet cells). **Mnemonic:** **GERD → METAPLASIA** — Gastroesophageal Reflux Disease → columnar Metaplasia (Barrett's) is the prototypical example taught in pathology.
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