Sonographic versus endoscopic retrograde cholangiographic measurements of the bile duct revisited: importance of the transverse diameter.

Abstract

The purpose of this study was to investigate how frequently the cross section of the bile duct is oval versus round on sonography and whether the transverse diameter of the bile duct (DTRV) on sonography corresponds better than the conventional anteroposterior diameter (DAP) to measurements on endoscopic retrograde cholangiography (ERC). In 44 consecutive patients with a DAP greater than or equal to 8 mm, DTRV was measured on short-axis sonograms. Diameter of the bile duct measured on ERC (DERC) was compared with DAP and DTRV in patients who underwent ERC shortly after sonography. The cross section of the bile duct was oval in 31 patients (70%). In 20 patients who underwent ERC after sonography, mean DERC was statistically indistinguishable from mean DTRV but statistically different from mean DAP. Comparing both DAP and DTRV with DERC in each patient, we found no statistically significant difference between DERC and DTRV, but we did find a statistically significant difference between DERC and DAP. An oval cross section is common in bile ducts with a DAP greater than or equal to 8 mm. The discrepancy between measurements of the bile duct made sonographically and those made on ERC is largely attributable to different cross-sectional diameters. Because DTRV correlates better than conventional DAP with DERC, measurement of DTRV can be helpful in confirming or excluding true biliary dilatation in patients with a DAP larger than normal.