A mathematical approach to the common bile duct.

Changes in the shape of the common bile duct (CBD) can be expressed mathematically by measuring the C.B.D.-diameter at five points and expressing these measurements as a percentage of the mean diameter. Variations in magnification are compensated for by relating the mean diameter to the length of the C.B.D. By comparing the shape of the C.B.D. in patients with various diseases with the shape of the normal common bile duct it was possible to define pathognomonic signs of various diseases of the extrahepatic biliary system. Indirect signs of pathology of the extrahepatic bile ducts are discussed.