Differentiation of Adenomyoma from Localized Adenocarcinoma of the Ampulla of Vater Using Multidetector CT

PURPOSE: To determine the multidetector CT (MDCT) findings that differentiate adenomyoma of the ampulla of Vater (AOV) from localized adenocarcinoma of the AOV. MATERIALS AND METHODS: Sixteen and 30 patients with adenomyoma and localized adenocarcinoma of the AOV, respectively, were evaluated using MDCT. We analyzed the size and attenuation value and presence of uniform enhancement of the lesions, diameters of the extrahepatic bile duct (EHD) and main pancreatic duct, presence of regional lymph node enlargement, and laboratory findings. We determined the independent findings for differentiating adenomyoma from localized adenocarcinoma of the AOV using multivariate analysis. RESULTS: The size of the lesion and diameter of the EHD were significantly smaller for adenomyoma than those for localized adenocarcinoma of the AOV (all p < 0.001). In multivariate analyses, a lesion size of ≤ 1.3 cm, an EHD diameter of ≤ 1.3 cm, and an alanine transaminase level of ≤ 31 IU/L significantly differentiated adenomyoma from localized adenocarcinoma of the AOV. When all of these three findings were met, the specificity for adenomyoma of the AOV was 93.3%. CONCLUSION: MDCT imaging may facilitate the differential diagnosis of adenomyoma and localized adenocarcinoma of the AOV based on the size of the lesion and diameter of the EHD.