A 62-year-old man presents with progressive painless jaundice, weight loss, and pruritus. Contrast-enhanced CT of the abdomen shows a hypoattenuating mass in the pancreatic head with a dilated common bile duct and the structure marked **C** (dilated main pancreatic duct). The radiologist reports a "double-duct sign." Which of the following best explains the pathophysiology of the dilated main pancreatic duct marked **C** in this clinical context?
A. Chronic inflammation of the pancreatic parenchyma leading to fibrosis and secondary duct stricture formation
B. Genetic mutation in the CFTR gene causing abnormal mucus secretion and duct plugging
C. Autoimmune destruction of pancreatic acinar cells resulting in loss of ductal compliance
D. Obstruction of the pancreatic duct by a mass at the pancreatic head causing upstream duct dilatation and parenchymal atrophy
Explanation
Why option 1 is correct
The double-duct sign—simultaneous dilatation of the common bile duct (B) and the main pancreatic duct (C)—is highly specific for an obstructing lesion at the pancreatic head or periampullary region. In this case, the hypoattenuating mass in the pancreatic head obstructs the main pancreatic duct (duct of Wirsung), causing upstream dilatation and downstream parenchymal atrophy. This is the classic pathophysiology of pancreatic ductal adenocarcinoma presenting with the double-duct sign. The patient's painless progressive jaundice, weight loss, and palpable gallbladder (Courvoisier sign) are consistent with head malignancy. (Sabiston Textbook of Surgery, 21st ed; Bailey & Love, 28th ed)
Why each distractor is wrong
Option 2 (Chronic inflammation): While chronic pancreatitis can rarely cause the double-duct sign, it typically presents with pain, calcification, and a different clinical picture. The acute presentation of painless jaundice with a discrete hypoattenuating mass is characteristic of malignancy, not chronic inflammation.
Option 3 (Autoimmune acinar destruction): Autoimmune pancreatitis does not cause the double-duct sign in the classic sense. It presents with diffuse pancreatic enlargement and elevated IgG4, not focal head mass with duct obstruction.
Option 4 (CFTR mutation): Cystic fibrosis causes diffuse pancreatic changes and duct plugging, not a focal obstructing lesion at the head with the double-duct sign. It typically presents in childhood with malabsorption and respiratory symptoms.
High-YieldNEET PG
Double-duct sign = simultaneous CBD + main pancreatic duct dilatation = obstructing lesion at pancreatic head or periampulla; most common cause is pancreatic ductal adenocarcinoma, which is hypoattenuating on contrast-enhanced CT due to dense desmoplasia and hypovascularization.
Sabiston Textbook of Surgery, 21st ed; Bailey & Love, 28th ed
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