Bile duct adenoma: a case report and literature review

As the imaging features of BDA are lacking in specificity, it is very hard to distinguish BDA from primary liver cancer. In this case, a plain CT scan showed that there was a nodular hypodense shadow of 1.5 cm with a hazy border close to the liver capsule in the juncture of segment 4 and 8 (Figure 6). The heterogeneity of the enhanced arterial phase was more intense; an abnormally enhanced ring-like peripheral shadow was also observed. A slightly or moderately enhanced flake-like change was identified in the hepatic tissue around the lesion, which, through maximum intensity projection and volume reconstruction, was shown to get blood supplied by the branch of the right hepatic artery (Figure 7 and Figure 8) and the lesions of both the portal and delayed phases showed a change of low density (Figure 9). The BDA lesions in the 6 cases reported by scholars such as Tajima were detected in the peripheral portion of the liver [2], and 5 of these took the form of hypervascular tumor, which are in accordance with the case we are studying. The CT enhancement method used in our case, however, is different from those in the cases mentioned above. This case being studied was initially misdiagnosed as hepatocellular carcinoma through a preoperative CT scan, the reason for which is that the CT scan demonstrated a typical “quick wash-in and wash-out” sign with an obvious nodular enhancement in the arterial phase of the lesion and low density change in the portal and delayed phases, all of which made it difficult for accurate diagnosis. In a report on BDA by Semelka et al., BDA appeared hypointense on T1-weighted images and hyperintense on T2-weighted images through MRI [3]. However, in the report by Maeda et al., T₂WI was considered as hypointense; it was proposed that the difference is caused by the number of the fibrous tissues in the tumor and whether there is calcification in the center of the tumor [4].

Traditionally speaking, BDA is a type of proliferative lesion originating from the damaged intrahepatic bile duct epithelium [5]. The main features of the pathology of BDA are as follows: i) The lesion is comparatively small, with a diameter between 1 to 20 mm. ii) The lesion is always detected under the hepatic capsule, usually taking the form of solitary nodule, occasionally of multiple nodules, with clear borders but without capsule. iii) The majority of the proliferated bile ducts are observed in the lesion, accompanied by plenty of chronic inflammatory cell infiltration; the epithelial cells of the proliferated bile ducts are well differentiated without obvious atypia. iv) As the disease progresses, the number of proliferated bile ducts and the infiltrated inflammatory cells gradually decreases, while that of fibrous tissues increases. In the late stage, the hyaline-degenerated collagen fibers occupy the region, with only a small amount of bile component and occasionally accompanied with calcification [6]. v) Immunohistochemical stains for CK7, CK19, and CD56 are positive, whereas for Ki67 and p53, stains are negative. In the present case, a large quantity of proliferated bile ducts can be observed, which are lined with single cuboidal epithelial cells with considerable inflammatory cell infiltration and hepatic steatosis (Figure 10), in accordance with the above pathological characteristics. In this case, the weakly positive immunohistochemical AFP and normal serum AFP show no significance in differentiating malignant tumors. Some scholars suggest that the lesion originates from a hamartoma of the glandular components around the bile ducts, and this lacking in atypical and gland mutation both contribute significantly to diagnosis. Further, the variation of the hyaline cell formation is very similar to renal-cell carcinoma. However, scholars, such as Saavedra [7], believe that the positive CK7, EMA, and CEA stains and negative Ki67 and CK20 stains can be helpful for differentiation.