False-positive CT diagnosis of gallstones due to thickening of the gallbladder wall.

An erroneous CT diagnosis of cholelithiasis was made at our institution during the past year in seven patients who had thickening of the gallbladder wall. In all cases the mucosa, which had a high attenuation value, was misinterpreted as a calcified stone, and the low-attenuation thickened submucosa was misinterpreted as intraluminal bile surrounding the stone. Depending on the attenuation of the actual intraluminal bile, the pseudostone appeared peripherally calcified (five patients) or uniformly calcified (two patients). Careful analysis of the position and configuration of a suspected stone and of the outer margin of the gallbladder can help avoid an incorrect CT diagnosis of gallstones when high-attenuation thickened mucosa simulates a gallstone and low-attenuation submucosa looks like surrounding bile.