Common bile duct stones: reassessment of criteria for CT diagnosis

To evaluate the specificity of previously suggested computed tomographic (CT) criteria for diagnosing common bile duct (CBD) stones, CT scans of 38 patients with CBD stones were compared with scans of 32 patients with carcinoma obstructing the CBD and 28 nonobstructed patients. The CBD stone was directly visualized as a target sign or densely calcified structure in 29 of 38 patients with stones (76%); one with carcinoma showed a similar target sign. A rim of increased density in the distal CBD was found without accompanying target sign in six patients with stones (16%), compared with 12 with carcinoma (38%) and 15 nonobstructed patients (54%). Irregular intraluminal densities without a detectable target sign were noted in four patients with stones (11%), compared with eight with carcinoma (25%) and nine nonobstructed patients (32%). Abrupt termination of the CBD without a mass was more common as an isolated finding in patients with carcinoma (31%) than in patients with stones (13%). CT is accurate in detecting CBD stones in certain patient populations, but direct visualization of the stone is required.