A 45-year-old woman with a history of previous abdominal surgery presents with acute abdominal pain and CT imaging shows multiple dilated small bowel loops with a transition point. Regarding the imaging features used to differentiate causes of mechanical small bowel obstruction, all of the following are correct EXCEPT:

Explanation

## Differentiation of Mechanical SBO Causes on Imaging ### Overview of Common Causes **Key Point:** CT imaging with multiplanar reconstruction is the gold standard for identifying both the presence and etiology of mechanical SBO. ### Evaluation of Each Statement | Cause | Imaging Features | True/False | |-------|------------------|------------| | Adhesions | Single transition zone, string sign, no mass/thickening | TRUE | | Crohn's disease | Skip lesions, segmental thickening, mesenteric fat stranding | TRUE | | Intussusception | Target sign (axial), sausage sign (coronal) | TRUE | | Hernias | Focal wall defect, internal > external herniation | FALSE | ### Why Hernias Are the Wrong Answer **High-Yield:** The epidemiology of hernias causing SBO is counterintuitive: - **External hernias** (inguinal, femoral, umbilical, incisional) account for **60–70%** of hernia-related obstructions - **Internal hernias** (through mesenteric defects, foramen of Winslow, paracolic gutters) account for only **5–10%** of hernia-related obstructions The statement incorrectly claims internal herniation is more common than external. ### Imaging Features of Each Cause #### Adhesions - Single transition zone (most common cause of SBO) - "String sign" — thin linear narrowing - No focal mass, no wall thickening - Normal bowel caliber distal to obstruction #### Crohn's Disease - **Skip lesions** — areas of normal bowel between diseased segments - Segmental wall thickening (>3 mm) - Mesenteric fat stranding ("comb sign") - Fibrofatty proliferation #### Intussusception - **Target sign** (axial CT) — concentric rings of alternating density - **Sausage sign** (coronal/sagittal) — elongated mass-like appearance - More common in pediatric population but can occur in adults with pathologic lead point #### Hernias - **External hernias:** Inguinal (most common), femoral, umbilical, incisional - **Internal hernias:** Rarer; through mesenteric defects, post-bariatric surgery - Imaging shows bowel loops exiting through focal defect **Clinical Pearl:** In post-surgical patients, adhesions remain the most common cause of SBO. Internal hernias are a consideration in post-bariatric surgery patients but are less common overall than external hernias. ### Mnemonic for SBO Causes **CHASM** — Crohn's, Hernias, Adhesions, Strictures, Masses (and Malrotation in pediatrics)