Abnormalities of the Distal Common Bile Duct and Ampulla: Diagnostic Approach and Differential Diagnosis Using Multiplanar Reformations and 3D Imaging

OBJECTIVE. The distal common bile duct (CBD) and ampulla are extremely difficult sites to evaluate on CT. This article seeks to provide the reader with a framework and algorithmic approach to the evaluation of abnormalities involving the distal CBD and ampulla, including an emphasis on the use of multiplanar reformations and 3D imaging, the morphologic features on CT that suggest the presence of malignancy, and a differential diagnosis for abnormalities in this location. CONCLUSION. In our experience, both the distal CBD and ampulla are common sites of missed diagnoses for radiologists. Avoiding mistakes in interpreting imaging findings in this location requires a systematic approach especially in the setting of unexplained biliary ductal dilatation. Rather than simply suggesting that MRCP or ERCP be performed for the ultimate diagnosis, radiologists can perform a careful CT evaluation using multiplanar reformations and 3D imaging to determine the correct diagnosis prospectively. A timely and correct diagnosis is imperative because lesions in the ampulla and CBD can be very aggressive despite their small size.