A 63-year-old woman was admitted with a history of recurrent episodes of right upper extremity pain for more than 8 years. Eight years prior, the patient had developed abdominal pain for no apparent reason. The pain spontaneously resolved after 20 min without any treatment. She experienced abdominal pain one to two times a year, which had increased in frequency and duration over the last 2 years. Abdominal pain was accompanied by nausea and vomiting; however, fever, chills, abdominal distension, and diarrhea were absent. The patient has no history of surgery, major trauma, or any chronic diseases such as hypertension or diabetes mellitus. She denied a history of any infectious diseases, such as hepatitis and tuberculosis, food and drug allergies, smoking, or alcohol consumption. Systemic skin, mucosa, and scleral icterus were absent. Her abdomen was supple and non-tender with no rebound tenderness. Abdominal varices were absent. The liver and spleen were not palpable below the costal margins. Percussion pain in the liver region, gastric, and intestinal shapes, and peristaltic waves were not observed. Murphy's sign was negative. Routine blood investigations, coagulation profiles, and tumor marker (carbohydrate antigen 19-9 and alpha-fetoprotein) levels were all normal. Computed tomography (CT) revealed intra- and extrahepatic biliary duct dilation; the maximum diameter of the common bile duct was 2.1 cm ( Figure 1 ). A 4-cm diameter cystic lesion was visualized in the caudate lobe of the liver ( Figure 1 ). Magnetic resonance (MR) images revealed a tumor-like tortuous dilation of the right hepatic duct at the hilum ( Figure 2 ); T1WI images showed a hypointense signal, and T2WI images showed a hyperintense signal. Tubular dilation of the common bile duct and left hepatic duct in the hilum was observed ( Figure 2 ). The terminal wall of the common bile duct was slightly thickened with a stenosed lumen and blockage. Enhancement of the bile duct wall was uniform and delayed. Sudden blockade of the terminal common bile duct ( Figure 3 ) and nodules on the magnetic resonance cholangiopancreatography (MRCP) ductal walls were observed. The clinical diagnosis was an intrahepatic bile duct cyst.
The patient underwent laparoscopic hepatectomy and choledochal exploration on January 6, 2021, with no contraindications for surgery. The gallbladder was enlarged during surgery, the common bile duct was wider (2 cm), and a cystic mass was located in the caudate lobe of the tail of the liver protruding toward the hepatogastric space. Intraoperatively, the diagnosis was changed to hepatobiliary cystadenoma. The hepatobiliary cystadenoma was resected, and the common bile duct was explored. The common bile duct was dissected, and a 1.5-cm longitudinal incision was made along it. A jellylike liquid was aspirated from the bile duct. Choledochoscopy revealed that the lower end of the common bile duct was patent without a tumor, left hepatic duct contained a cloudy exudate, and opening of the bile duct tumor was located in the left caudate lobe. A 0.6-cm-wide bile duct converged with the left bile duct at the tumor site. The duct was resected and ligated, and tumor was completely resected and sent for histopathological examination. Rapid pathological examination revealed a mucoepithelial cyst in the caudate lobe with mild-to-moderate atypia, suggesting a mucinous cystic neoplasm.
The surgery was successful, and the patient recovered well. She was discharged 3 days after surgery. Pathological examination of the paraffin sections ( Figures 4 ,  5 ) revealed an IPNB, a low-grade cystic lesion measuring 4.5 cm x 3.5 cm in volume with cells rich in mucus, which met the definition of BT-IPMN. Immunohistochemistry revealed estrogen receptor (-) and Ki-67 expression (40%). The patient visited the outpatient clinic irregularly after surgery until November 2021 to observe tumor recurrence. To date, no tumor recurrence has been observed.