The transverse common duct.

The sonographic appearance and incidence of transverse common ducts were studied. A review of 118 intraoperative cholangiograms showed a transverse segment longer than 35 mm in 18% of the dilated extrahepatic ducts and in 6% of the normal caliber ducts. The causes of obstruction varied. When dilated, the transverse segment may be confused with the portal and splenic veins on a sonogram. An awareness of this anatomic variation can be helpful in locating an obstructing lesion of the extrahepatic bile duct.