## Investigation of Choice for Perforation Localization **Key Point:** CT abdomen and pelvis with IV contrast is the gold standard for identifying the site, cause, and complications of hollow viscus perforation. ### Why CT is Superior | Feature | Erect CXR | CT with IV Contrast | Ultrasound | Barium | |---------|----------|-------------------|-----------|--------| | **Detects pneumoperitoneum** | Yes (>1 mL air) | Yes | Limited | No | | **Identifies perforation site** | No | Yes (95% sensitivity) | No | Contraindicated | | **Shows cause (ulcer, tumor, diverticulum)** | No | Yes | No | Contraindicated | | **Evaluates peritonitis severity** | No | Yes | Limited | Contraindicated | | **Assesses organ viability** | No | Yes (perfusion) | No | No | | **Time to diagnosis** | Immediate | 5–10 min | Operator-dependent | Prolonged | **High-Yield:** CT with IV contrast demonstrates: 1. **Pneumoperitoneum** — free air in peritoneal cavity 2. **Site of perforation** — focal defect in bowel wall with air leak 3. **Cause** — peptic ulcer, diverticulitis, malignancy, trauma, ischemia 4. **Complications** — abscess formation, peritonitis, sepsis 5. **Organ perfusion** — helps assess viability (ischemic vs. traumatic) ### Clinical Pearl While erect CXR is the **initial screening tool** (bedside, rapid, no contrast needed), it only confirms pneumoperitoneum but does NOT identify the site or cause. In a haemodynamically stable patient with confirmed perforation, CT is mandatory before surgery to guide operative planning. ### Mnemonic: **SITE** - **S** — Site of perforation (CT shows this) - **I** — Identify cause (ulcer? diverticulum? tumor?) - **T** — Track complications (abscess, fistula) - **E** — Evaluate organ viability (perfusion assessment) **Warning:** Barium studies and oral contrast are **absolutely contraindicated** in suspected perforation — risk of barium peritonitis and sepsis. 
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