A 52-year-old man with a history of peptic ulcer disease presents with acute severe epigastric pain and abdominal rigidity. CT imaging shows pneumoperitoneum with gas localized to the anterior pararenal space and lesser sac. Which imaging feature best distinguishes perforation of an anterior gastric ulcer from a posterior gastric ulcer?

Explanation

## Distinguishing Anterior vs Posterior Gastric Ulcer Perforation ### Anatomical Basis **Key Point:** Anterior gastric ulcer perforation leads to free pneumoperitoneum with gas tracking into the anterior pararenal space and lesser sac, while posterior gastric ulcer perforation may be contained or present with gas in the retroperitoneal space. Anterior gastric wall perforations communicate directly with the peritoneal cavity, allowing rapid dissemination of gas throughout the peritoneal space. Posterior gastric wall perforations, however, are bounded by the posterior peritoneal reflection and gastrocolic ligament, often resulting in: - Retroperitoneal gas (pneumoretroperitoneum) - Gas localized to the lesser sac and paracolic gutters - More contained presentation with potential for walling off ### Imaging Findings Comparison | Feature | Anterior Gastric Ulcer | Posterior Gastric Ulcer | |---------|------------------------|------------------------| | **Free gas distribution** | Diffuse peritoneal, anterior pararenal space, lesser sac | Retroperitoneal, lesser sac, may be loculated | | **Pneumoperitoneum extent** | Extensive, widespread | May be minimal or absent | | **Retroperitoneal gas** | Absent or minimal | Present and prominent | | **Clinical presentation** | Acute, fulminant peritonitis | May be more indolent | ### High-Yield Imaging Pearls **High-Yield:** The **anterior pararenal space and lesser sac localization** is the pathognomonic finding for anterior gastric ulcer perforation and is the single best discriminator on CT imaging. **Clinical Pearl:** Posterior gastric ulcer perforations may present with a more insidious clinical course because the perforation is contained by posterior peritoneal attachments, occasionally allowing for spontaneous sealing or formation of a localized abscess. **Tip:** On axial CT, look for gas tracking along the anterior surface of the stomach and within the lesser sac (anterior to the pancreas) — this is diagnostic of anterior perforation.