A 45-year-old man with a 10-year history of alcohol use disorder presents to the emergency department with acute onset epigastric pain radiating to the back, associated with vomiting. On examination, he is febrile and tachycardic. A supine abdominal radiograph is obtained as part of the initial imaging workup. The structure marked **A** in the diagram shows a focal, gas-filled dilated loop of small bowel in the left upper quadrant adjacent to the pancreas. Which of the following best describes the pathophysiological mechanism underlying this radiological finding?
A. Generalized adynamic ileus secondary to systemic inflammatory response
B. Localized peritonitis-induced paralysis of the jejunum adjacent to the inflamed pancreas
C. Mechanical obstruction of the duodenum by pancreatic edema
D. Volvulus of the small bowel loop due to pancreatic traction
Explanation
Why "Localized peritonitis-induced paralysis of the jejunum adjacent to the inflamed pancreas" is right
The sentinel loop sign (marked A) is a classic plain-film radiological finding in acute pancreatitis, representing a focal, gas-filled small bowel loop (typically jejunum) in the left upper quadrant that appears dilated and paralyzed. This occurs due to localized peritonitis caused by inflammatory exudate from the acutely inflamed pancreas, which induces segmental ileus in the adjacent bowel loop. According to the Revised Atlanta Classification 2012 and AGA guidelines, this is one of the characteristic imaging findings that can support the diagnosis of acute pancreatitis when combined with clinical presentation and biochemical markers (serum lipase or amylase >3× upper limit normal). The sentinel loop is a sign of localized, not generalized, bowel dysfunction.
Why each distractor is wrong
Mechanical obstruction of the duodenum by pancreatic edema: While pancreatic edema can occur in acute pancreatitis, the sentinel loop is not a mechanical obstruction but rather a paralyzed segment due to localized inflammation. Mechanical obstruction would present differently on imaging (transition point, proximal dilation with distal collapse).
Generalized adynamic ileus secondary to systemic inflammatory response: Although generalized ileus can occur in severe pancreatitis, the sentinel loop is specifically a focal, localized finding adjacent to the pancreas, not a diffuse pattern. The distinction between localized peritonitis-induced paralysis and generalized ileus is critical.
Volvulus of the small bowel loop due to pancreatic traction: Volvulus is a mechanical twisting of bowel and would show a different radiological pattern (whirl sign on CT, transition point). The sentinel loop is purely functional paralysis, not mechanical torsion.
High-YieldNEET PG
Sentinel loop = focal jejunal paralysis from localized peritonitis adjacent to inflamed pancreas; colon cut-off sign = splenic flexure gas termination from phrenicocolic ligament inflammation.
Revised Atlanta Classification 2012; AGA Acute Pancreatitis Guidelines 2018
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