Optimization of Patient Positioning for the Sonographic Evaluation of Gallstone Impaction: Analysis of Gallbladder Orientation Based on Computed Tomography.

An important sonographic sign of cholecystitis is stone impaction in the gallbladder neck. Demonstration of stone mobility excludes impaction. The purpose of this study is to analyze the orientation of the gallbladder on computed tomography and determine the patient position most likely to facilitate stone mobility. ImageJ processing software was used to determine the x (transverse), y (anterior-posterior), and z (craniocaudal) coordinates for the gallbladder neck and fundus in 544 consecutive computed tomography examinations. The differences in the fundal and neck coordinates were used to determine the likelihood of moving a stone from the neck to the fundus for the left and right lateral decubitus positions ( x coordinates), the prone position ( y coordinates), and the upright position ( z coordinates). The coordinate with the largest difference was considered to predict the position most likely to facilitate stone motion. The difference in position of the fundus and neck was greatest in the y -, z -, and x -axis in 232 (42.6%), 194 (35.7%), and 118 (21.7%) of patients, respectively. For body mass index (BMI) less than 25 kg/m 2 , the difference was greatest in the z -axis (59.8%). For BMI greater than 25 kg/m 2 , the difference was greatest in the y -axis (47.1%). Based on their relative location, the optimal position to facilitate gallstone mobility from the gallbladder neck to fundus was most often prone (especially in high BMI patients), followed by upright (especially in low BMI patients), followed by right lateral decubitus. The left lateral decubitus position was never optimal.