A 38-year-old woman with a history of peptic ulcer disease presents with acute peritonitis. CT abdomen shows free air in the peritoneal cavity. Regarding the imaging characteristics of different types of hollow viscus perforation, all of the following statements are correct EXCEPT:

Explanation

## Imaging Characteristics of Hollow Viscus Perforation by Site **Key Point:** The distribution and characteristics of free air vary significantly depending on the site of perforation, reflecting the anatomy and contents of each viscus. ### Comparison of Perforation Sites | Site | Volume of Air | Distribution | Associated Features | Clinical Course | |------|---------------|--------------|---------------------|----------------| | **Gastric** | Large | Diffuse pneumoperitoneum | Rapid onset, high acid content | Rapid deterioration | | **Duodenal** | Variable | Retroperitoneal (D2-D4) or intraperitoneal (D1) | Retroperitoneal tracking | May be delayed presentation | | **Small bowel** | Moderate to large | Loculated collections, diffuse | Feculent peritonitis if delayed | Depends on delay | | **Colonic** | Small to moderate | Pelvis, along fascial planes | Feculent peritonitis, tracking | Often delayed diagnosis | ### Analysis of Each Option **Option A — Gastric Perforation (TRUE)** - Large volume pneumoperitoneum due to gastric air content - Rapid clinical deterioration from gastric acid and bacterial contamination - Often presents with dramatic findings on imaging **Option B — Small Bowel Perforation (TRUE)** - Loculated free air collections due to bowel loops and adhesions - Feculent peritonitis if perforation is delayed (hours to days) - Small bowel contents are highly contaminated **Option C — Colonic Perforation (FALSE — THIS IS THE ANSWER)** **High-Yield:** Colonic perforation characteristically shows: - **Large volume of free air** (not minimal) due to high bacterial load and gas-producing organisms - **Diffuse pneumoperitoneum** (not localized to pelvis) - **Extensive fascial plane tracking** with air extending along retroperitoneal planes - **Feculent peritonitis** — the most contaminated type The statement claims "minimal free air in the pelvis," which is **incorrect**. Colonic perforation typically produces **abundant free air** that distributes widely throughout the peritoneal cavity and along fascial planes. **Option D — Duodenal Perforation (TRUE)** - D2, D3, D4 portions are retroperitoneal - Perforation may present with retroperitoneal free air first - Can have delayed presentation if contained by retroperitoneal structures **Clinical Pearl:** Colonic perforation is the most contaminated type of hollow viscus perforation and produces the most abundant free air. The retroperitoneal duodenum, by contrast, may initially contain air in the retroperitoneum, limiting early intraperitoneal spread.