A 40-year-old alcoholic man presents with severe epigastric pain radiating to the back. Plain abdominal radiograph shows a focally distended loop of jejunum in the left upper quadrant with an air-fluid level, while the rest of the bowel appears normal. Which mechanism best explains this finding?

• A Mechanical obstruction at the duodenojejunal flexure
• B Localized paralytic ileus adjacent to the inflamed pancreas ✓
• C Jejunal diverticulosis with bacterial overgrowth
• D Superior mesenteric artery syndrome

Explanation

This is a sentinel loop, a solitary distended jejunal loop reflecting localized reflex paralysis of bowel contiguous with an inflamed organ, classically acute pancreatitis. Inflammatory exudate irritates the adjacent serosa, producing a localized adynamic segment while the remaining bowel retains normal calibre. Mechanical obstruction would produce dilatation of multiple loops with a step-ladder pattern, and SMA syndrome produces duodenal rather than jejunal dilatation. A related sign, the colon cut-off, shows abrupt gas arrest at the splenic flexure.

Reference: Grainger and Allison's Diagnostic Radiology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.