Sonographic parallel channel sign: a reappraisal.

Tubular structures proximal to the right and left hepatic ducts, when seen with ultrasonography, are generally considered to be abnormally dilated ducts. However, newer, electronically focused transducers reveal peripheral tubular structures paralleling portal venous branches. The diameters of all visible tubular structures that would have been thought to be bile ducts were measured in 50 persons with no evidence of hepatobiliary disease. "Ducts" were seen with the following frequencies: right hepatic, 100%; right anterior, 100%; right posterior, 88%; left hepatic, 98%; left medial, 62%; left lateral, 96%; left lateral superior, 54%; and left lateral inferior, 54%. All ducts proximal to the right and left hepatic ducts were 2 mm or less in diameter. Those proximal to the common hepatic ducts averaged approximately 20% of the diameters of their accompanying portal veins. Except for 4% of the left lateral inferior ducts, no ducts proximal to the common hepatic ducts were more than 40% the diameter of their respective portal vein branches. Mere observation of parallel channels proximal to the right and left hepatic ducts is therefore not evidence of biliary dilatation.