Magnification of the endoscope during endoscopic retrograde cholangiography--a reliable standard for exact measurement of bileduct and bilestones.

In 57 patients undergoing endoscopic retrograde cholangiography (ERC) the magnification of the endoscope was determined by measurement of its diameter depicted on the X-rays. A magnification of 30.2 +/- 10.6% (mean +/- SD) ranging from 8 to 58% in individual patients was recorded. The clinical reliability of the method was confirmed by comparing the diameters of 13 bile duct stones assessed in-situ and after removal respectively. Although the magnification tended to be higher in obese patients, no correlation between body weight and the degree of the magnification could be established. Our data add further doubt to the reliability of the radiologic bile duct measurement if not referred to a reliable standard which can be easily provided by the endoscope. This is particularly important whenever therapeutic interventions are planned which critically depend on exact determination of diameters, like bile duct stone removal with or without endoscopic papillotomy, lithotripsy or introduction of transpapillary enthoprothesis.