1926. Utilizing CT to Identify Clinically Significant Biliary Dilatation in Post-Cholecystectomy Patients
Authors * Denotes Presenting Author
  1. Imo Uko *; Northwestern University
  2. Edward Nguyen; Northwestern University
  3. Annie Huang; Northwestern University
  4. Cecil Wood; Northwestern University
  5. Rajesh Keswani; Northwestern University
  6. Frank Miller; Northwestern University
  7. Linda Kelahan; Northwestern University
Post cholecystectomy biliary dilatation is an expected finding on imaging (1–4), however, there is no current consensus on what a normal common bile duct (CBD) threshold diameter is in these patients. Our study aims to determine a reliable threshold CBD diameter at CT, in combination with ancillary CT findings, at which the likelihood of pathology requiring further imaging or intervention is increased in symptomatic post-cholecystectomy patients.

Materials and Methods:
This retrospective study was IRB-approved. Two attending radiologists independently reviewed CT imaging for 50 post-cholecystectomy patients. Patients were grouped by whether they had findings requiring intervention on MRCP, ERCP or EUS or had normal follow-up imaging (no etiology for biliary ductal dilatation other than post cholecystectomy state). Pertinent baseline lab values and demographics were obtained. Measurements of the CBD were obtained at the porta-hepatis, distal duct, and point of maximal dilation on axial and coronal CT abdomen. The presence or absence of intrahepatic and pancreatic ductal dilatation on CT was assessed.

Preliminary evaluation of 50 of the 134 identified patients which included 21 patients with abnormal follow-up imaging and 29 with normal follow-up was performed. Mean axial and coronal CBD diameters were statistically significantly greater in the group with abnormal follow-up at all locations, with mean difference between the maximal CBD measurements in the coronal plane the most statistically significant. Mean CBD diameters at the point of maximal dilatation in the abnormal follow-up and normal follow-up groups were 15.7 ± 1.1 mm and 12.6 ± 0.5 mm in the coronal plane, and 15.1 ± 1.2 mm and 12.3 ± 0.6 mm in the axial plane. Mean difference between both groups at point of max CBD dilatation was 3.2mm (p=0.005), in the coronal plane and 2.8mm (p=0.03), in the axial plane. Inter-rater reliability analysis was excellent (> 0.75) between readers for all CBD measurements with the highest inter-rater correlation (0.86) noted for axial CBD max diameter measurements. In the group with abnormal follow-up imaging, there were significant increases in direct and total bilirubin (P < 0.05).

Differences in axial and coronal CT CBD diameter measurements in post-cholecystectomy patients with and without significant causes for biliary dilation were shown to be statistically significant, with mean difference between the maximal CBD measurements in the coronal plane the most statistically significant, and maximal CBD measurements in the axial plane the most reproducible between radiologists. Biliary ductal dilatation is a common incidental CT finding seen in symptomatic post-cholecystectomy patients initially imaged with CT. However, distinguishing actionable etiologies of biliary ductal dilatation in this patient population is challenging for radiologists. Establishing CT CBD measurements in this patient population can help reduce cost and unnecessary follow-up imaging.