On CT imaging, which finding is the most sensitive indicator of acute bowel perforation?

Explanation

## Extraluminal Contrast Extravasation — Highest Sensitivity **Key Point:** On contrast-enhanced CT, **extraluminal contrast extravasation** (leakage of oral or IV contrast outside the bowel lumen into the peritoneal cavity or retroperitoneum) is the most sensitive and direct sign of bowel perforation. ### Why Extraluminal Contrast Extravasation Is Most Sensitive 1. **Direct visualization of breach** — the contrast physically leaks through the perforation site 2. **Sensitivity: 75–90%** — detected in the majority of acute perforations on contrast-enhanced CT 3. **Specificity: 95–100%** — virtually diagnostic when present 4. **Works even with small perforations** — even tiny defects allow contrast to escape ### Comparison of CT Signs of Perforation | Sign | Sensitivity | Specificity | Notes | |------|-------------|-------------|-------| | Extraluminal contrast | 75–90% | 95–100% | **Most sensitive** — direct evidence | | Pneumoperitoneum | 50–85% | 70–80% | Absent in 15–50% of perforations | | Focal bowel wall discontinuity | 40–60% | 85–90% | Requires high-resolution imaging | | Peritoneal fat stranding | 60–80% | 50–60% | Non-specific — seen in peritonitis from any cause | | Portal venous gas | 10–20% | 95%+ | Rare but highly specific | **High-Yield:** **Pneumoperitoneum alone is absent in up to 50% of perforations**, especially early or in small perforations. Contrast extravasation is therefore a more reliable sign. **Clinical Pearl:** In patients with **contraindications to oral contrast** (suspected perforation, ileus), **IV contrast alone** can still demonstrate extravasation at the perforation site, making this the most practical sensitive sign. **Mnemonic: ESCAPE** — **E**xtraluminal **S**eepage of **C**ontrast = **A**cute **P**erforation **E**vidence.