Diffusion-Weighted MRI in Intrahepatic Bile Duct Adenoma Arising from the Cirrhotic Liver
A 64-year-old male patient with alcoholic liver cirrhosis, who was under surveillance for hepatocellular carcinoma (HCC), showed a mass-like lesion on a computed tomography (CT) scan. The CT scan performed 22 months earlier had revealed no abnormal lesion in the liver. Liver function tests on admission showed elevated serum aminotransferases, with a glutamic-oxaloacetic transaminase level of 121 IU/L (normal = 15-41 IU/L) and a glutamic-pyruvic transaminase level of 69 IU/L (normal = 17-59 IU/L). The serological workups for the hepatitis B virus antigen and hepatitis C virus antibody were negative, and the serum alpha-fetoprotein level was normal.\nDynamic CT scan was performed with a multi-detector row scanner (Somatom Definition Flash, Siemens Healthcare, Forchheim, Germany) before and after the intravenous injection of 2 mL/kg of non-ionic, iodinated contrast material (Xenetix 300, iobitridol; Guerbet, Sulzbach, Germany). Unenhanced images showed a newly developed 1.4-cm low-density subcapsular mass in the left lateral segment of the liver (). On dynamic contrast-enhanced images, the mass demonstrated homogeneous enhancement in the arterial phase (18 seconds after the injection of contrast material) and persistent enhancement in the portal venous phase (60 seconds) but appeared to be isoattenuated relative to the liver parenchyma in the delayed phase (180 seconds) (). The CT parameters were as follows: detector collimation, 0.63 mm; reconstruction interval, 3 mm; tube voltage, 120 kVp; and the product of the tube current and exposure time, 50-240 mAs in conjunction with dose modulation techniques.\nLiver dynamic MRI was performed one week later to rule out the possibility of small HCC with a 3-T whole-body MRI system (Intera Achieva 3.0T, Philips Medical System, Best, the Netherlands). On T2-weighted images, the mass showed high signal intensity. On T1-weighted images, it showed low signal intensity. On dynamic MRI using Gd-EOB-DTPA (Primovist, Bayer Schering Pharma, Berlin-Wedding, Germany; 0.025 mmol/kg), the mass showed strong enhancement in the arterial and portal venous phases (30 and 70 seconds after the injection of Gd-EOB-DTPA, respectively) but was isointense to the liver parenchyma in the late dynamic phase (180 seconds) (). In hepatobiliary phase images, which were obtained 20 minutes after the injection, the mass was distinctly hypointense (). Respiratory-triggered DWI sequences were performed with single-shot echo planar imaging with b values of 0, 50, 400, and 800 s/mm2. The apparent diffusion coefficient (ADC) was automatically calculated by the MR system and displayed as the corresponding ADC map. The mass showed high signal intensity on DWI even at high b-values and exhibited high signal intensity on the ADC map. The ADC value (2.21 × 10-3 mm2/s) of the tumor was more than twofold that of the surrounding liver parenchyma (1.01 × 10-3 mm2/s), which indicates that the hyperintensity seen on high b-value DWI was due to a very high signal intensity on T2-weighted images rather than diffusion restriction ().\nInitially, our first impression was that the patient had a benign enhancing nodule, such as focal nodular hyperplasia (FNH), FNH-like lesion, small hemangioma or dysplastic nodule. However, the possibility of HCC could not be ruled out. When all the possible diagnoses were explained to the patient, he chose to have the mass resected and underwent left lateral segmentectomy at our institution.\nA gross inspection of the specimen showed an ill-defined yellowish nodule located about 0.5 cm from the hepatic capsule, measuring about 1.2 × 1 cm. Microscopically, a proliferation of well-formed bile ductules on a background of fibrous stroma was noted without cellular atypia or mitotic activity (). The result from immunohistochemical stain was negative for carcino-embryonic antigen and p53, but positive for cytokeratin-19. The absence of p53 helps differentiate bile duct adenoma from metastatic adenocarcinoma. The presence of cytokeratin-19 shows that the nodule is of bile duct origin (). The histologic diagnosis was intrahepatic bile duct adenoma on a background of alcoholic liver cirrhosis.