Posterior superior pancreaticoduodenal vein: mimic of distal common bile duct at sonography.

OBJECTIVE

Previous investigators have noted that the common bile duct may appear to merge with the portal vein on sagittal sonograms, mimicking a venous structure. The posterior superior pancreaticoduodenal vein courses adjacent to the distal part of the common bile duct within the pancreatic head. A prospective study was performed to assess the sonographic appearance of the posterior superior pancreaticoduodenal vein.

SUBJECTS AND METHODS

The study included 50 consecutive subjects in whom the pancreatic head was well seen. Anatomic characteristics of the posterior superior pancreaticoduodenal vein were noted with gray-scale, duplex Doppler, and color Doppler sonography. The site of insertion of the posterior superior pancreaticoduodenal vein into the portal vein was noted.

RESULTS

The posterior superior pancreaticoduodenal vein was visualized in all 50 cases. Although it usually (82% of cases) inserted into the posterior aspect of the portal vein, the posterior superior pancreaticoduodenal vein inserted into the anterior aspect of the portal vein in nine cases (18%), resulting in an appearance mimicking the common bile duct on sagittal sonograms. Doppler examination showed flow toward the portal vein in all obliquely oriented posterior superior pancreaticoduodenal veins, and in 40% overall. The common bile duct could always be followed into the porta hepatis and was anterior to the posterior superior pancreaticoduodenal vein in 49 cases (98%).

CONCLUSION

The posterior superior pancreaticoduodenal vein can be seen routinely on sonograms when the pancreatic head is unobscured, and it can mimic the common bile duct in a significant number of cases. These structures can be distinguished by noting continuation of the common bile duct into the porta hepatis, the generally anterior position of the common bile duct, and flow in the posterior superior pancreaticoduodenal vein on Doppler examination. Awareness of the existence and anatomy of the posterior superior pancreaticoduodenal vein minimizes its confusion with the common bile duct at sonographic examination.