## Most Common Site of Peptic Ulcer Perforation **Key Point:** The anterior wall of the first part (D1) of the duodenum is the most common site of peptic ulcer perforation, accounting for approximately 60–70% of all perforated peptic ulcers. ### Anatomical Basis The anterior duodenal wall is vulnerable because: - It lacks the protective retroperitoneal attachment that the posterior wall enjoys - The anterior surface is directly exposed to the peritoneal cavity - Ulcers here erode through the thin anterior wall into the free peritoneum, causing acute pneumoperitoneum ### Imaging Findings in Anterior Duodenal Perforation | Feature | Finding | |---------|----------| | **Free air location** | Anterior pararenal space, anterior to duodenum | | **Air distribution** | Pneumoperitoneum (often localized initially) | | **Associated findings** | Duodenal wall thickening, sentinel clot | | **CT sensitivity** | >95% for detecting free air | ### Posterior Duodenal Perforation — Why Different **Clinical Pearl:** Posterior duodenal ulcer perforation is less common (~25% of cases) because the posterior wall is protected by the retroperitoneum. When perforation occurs, air may track into the retroperitoneal space rather than causing acute peritonitis, leading to delayed or atypical presentation. **High-Yield:** Anterior perforation → acute peritonitis + obvious pneumoperitoneum. Posterior perforation → retroperitoneal abscess + subtle presentation. ### Why Stomach Perforations Are Less Common Gastric ulcer perforation accounts for only ~10–15% of perforated peptic ulcers. When gastric ulcers do perforate, they are more commonly located on the anterior wall of the antrum or along the lesser curvature, but these are far less frequent than duodenal perforation. **Mnemonic:** **DUO-ANTE** = DUodenal-ANTErior is the most common site.
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