Which radiological sign on plain abdominal X-ray is pathognomonic for small bowel obstruction and represents air within the bowel wall?

Explanation

## Pneumatosis Intestinalis in Small Bowel Obstruction **Key Point:** Pneumatosis intestinalis is air within the submucosa or muscularis of the bowel wall, appearing as linear or cystic lucencies parallel to the bowel lumen on plain radiographs. **High-Yield:** While pneumatosis can occur in various conditions (necrotizing enterocolitis, inflammatory bowel disease, post-surgical states), in the context of mechanical small bowel obstruction it indicates **ischemia and is a sign of bowel necrosis**. ### Rigler's Triad vs. Pneumatosis | Finding | Composition | Significance | |---------|-------------|-------------| | **Rigler's Triad** | (1) Small bowel air, (2) Colonic air, (3) Air in biliary tree | Indicates gallstone ileus; classic triad | | **Pneumatosis Intestinalis** | Air in bowel wall itself | Ischemia, necrosis, surgical emergency | **Clinical Pearl:** Pneumatosis + portal venous gas = **surgical emergency**; indicates transmural necrosis and perforation risk. **Mnemonic:** **PNEUM** = **P**athognomonic for **N**ecrosis in **E**mergent **U**nstable **M**echanical obstruction. ### Why This Matters - Pneumatosis is a **red flag** for bowel viability compromise - Requires urgent surgical evaluation - Often associated with free air (perforation) or portal venous gas [cite:Robbins & Cotran 10e Ch 17]