1397 Intrahepatic Bile Duct Adenoma: A Diagnostic Dilemma

Abstract

INTRODUCTION: Intrahepatic bile duct adenoma (BDA) is a rare tumor arising from the epithelial cells of the bile ducts. BDA has been usually found incidentally by intra-abdominal surgery and autopsy. BDA is clinically significant because of its benign prognosis but also its difficulty differentiating from malignant neoplasms of the liver by imaging studies. CASE DESCRIPTION/METHODS: A 52-year-old male presented with hematuria. A CT abdomen and pelvis showed an incidental, 1.5 cm lesion in the right hepatic lobe. Following fine needle aspiration biopsy of the lesion, the tissue demonstrated a slightly irregular hepatic duct proliferation, for which a differential diagnosis of bile duct adenoma and well-differentiated cholangiocarcinoma was considered. Alpha-fetoprotein, carbohydrate antigen 19-9, and carcinoembryonic antigen were normal. An MRI was obtained to better ascertain the lesion, which demonstrated a 1.1 × 1.1 cm lesion within the right hepatic lobe, segment 6. The decision was made to pursue a hepatic resection. On gross examination, the specimen revealed an ovoid, well-circumscribed, white-tan, firm lesion measuring 1.4 cm in greatest dimension, and located 0.5 cm from the hepatic capsule. Microscopically, there was a well-circumscribed lesion composed of small biliary-type glands in tubular and branching trabecular patterns with a mild nuclear enlargement and inconspicuous mitotic activity. The lesion was well-delineated and the interphase with hepatocytes was regular without infiltrative growth (Figure 2). Immunohistochemically, CD56 stain was focally positive in the tumor. DISCUSSION: The main characteristics of BDA are as follows: the lesion is small-sized, with a diameter ranges between 1 to 20 mm; the lesion is always detected under the hepatic capsule, with clear borders but without capsule; the majority of the proliferated bile ducts are observed in the lesion, accompanied by plenty of chronic inflammatory cell infiltration; immunohistochemical stain for CK7, CK19, and CD56 are positive, whereas Ki67 and p53 are negative. Gütgemann et al. suggested that CD56 expression can aid the differential diagnosis of cholangiocarcinoma and a benign lesion such as BDA. Since our case showed positive CD56 stain along with other aforementioned features, the appropriate diagnosis was BDA. Since there are no definite imaging characteristics or tumor markers that allow a preoperative diagnosis, surgical resection followed by microscopic and immunohistochemical findings is crucial for the diagnosis of BDA.