How to describe pancreas divisum, including complete and partial divisum, in Endoscopic Ultrasound (EUS)?

Endoscopic Ultrasound Description of Pancreas Divisum

During linear-array EUS, pancreas divisum is diagnosed by the absence of a continuous main pancreatic duct from the major papilla into the pancreatic body and the absence of a visible ventral-dorsal duct transition, with complete divisum showing no communication between ductal systems and partial divisum showing filamentous communication between the ventral and dorsal ducts. 1, 2

Complete Pancreas Divisum

Primary EUS Findings

• Absent "stack sign": The classic parallel arrangement of the bile duct and pancreatic duct running together through the pancreatic head cannot be visualized in 67% of complete divisum cases, as the ventral duct is too short to create this appearance 3

• Discontinuous main pancreatic duct: The main pancreatic duct cannot be followed continuously from the major papilla into the pancreatic body, which is the most reliable sign for complete divisum 2

• Absent ventral-dorsal duct transition: No sonographic crossing point is visible where the ventral and dorsal pancreatic ducts would normally fuse, indicating complete failure of embryologic fusion 2

• Separate duct openings with no communication: The ventral and dorsal ductal systems drain independently through the major and minor papillae respectively, with no visible connection between them 1

Technical Approach

• Position the linear echo endoscope in the duodenal bulb with the transducer in long scope position, inflate the balloon, and advance snugly into the apex of the bulb to attempt visualization of the stack sign 3

• Follow the main pancreatic duct from the major papilla—in complete divisum, the duct will be short (representing only the ventral duct) and will not continue into the pancreatic body 2

• The dominant dorsal duct drains through the minor papilla and can be visualized separately in the pancreatic body and tail 1

Partial Pancreas Divisum

Distinguishing Features

• Filamentous communication: A thin, thread-like connection exists between the ventral and dorsal ductal systems, distinguishing partial from complete divisum 1

• "Crossed duct sign": The ventral and dorsal ducts may be seen crossing each other with minimal communication on linear EUS 1

• Short ventral duct with communication: Unlike complete divisum, there is some degree of fusion between the ductal systems, though the ventral duct remains abbreviated 1

Additional EUS Signs

• "Duct above duct" appearance: The dorsal and ventral ducts may be visualized in a stacked configuration with visible communication 1

• Ventral-dorsal duct transition: A crossing point may be visible, but the ventral duct contribution is minimal compared to the dominant dorsal system 1

Indirect EUS Findings

• Santorinecele: Bulging of the minor papilla may be visible, suggesting increased flow through the dorsal duct system 1

• Dominant dorsal duct: The duct draining through the minor papilla is larger in caliber than the ventral duct, indicating the dorsal system carries the majority of pancreatic drainage 1

• Dilated ventral duct: In rare cases where the stack sign is visible in divisum patients, the ventral duct may be markedly dilated (>6 mm), making it visible despite the anatomic variant 3

Diagnostic Performance

• Linear-array EUS has 95% sensitivity, 97% specificity, and 97% overall accuracy for identifying pancreas divisum when adequate duct visualization is achieved 2

• Adequate EUS evaluation of the pancreatic duct is possible in approximately 78% of patients 2

• The positive predictive value is 86% and negative predictive value is 99% for EUS diagnosis of pancreas divisum 2

Common Pitfalls

• False negative stack sign: The stack sign may occasionally be visible in divisum patients if the ventral duct is markedly dilated or if the ventral pancreas is unusually large, potentially leading to missed diagnosis 3

• Inadequate duct visualization: In 22% of cases, technical factors prevent adequate evaluation of the pancreatic ductal anatomy, limiting diagnostic accuracy 2

• Confusing partial with complete divisum: Careful attention must be paid to identifying any filamentous communication between ductal systems to distinguish partial from complete variants 1