S5407 An Unusual Tumor in an Uncommon Patient: Hepatic Mucinous Cystic Neoplasm Causing Biliary Obstruction

Introduction: Mucinous cystic neoplasms of the liver (MCN-L) are a rare subset of cystic hepatic tumors representing less than 5% of hepatic cysts. They occur exclusively in middle-aged womans and carry a malignant potential, having been historically termed biliary cystadenoma/cystadenocarcinoma. MCN-L usually arises within the liver parenchyma and, less frequently, involves the extrahepatic bile ducts. Here we discuss a rare presentation of MCN-L manifesting as obstructive jaundice. Case Description/Methods: A 22-year-old previously healthy woman with a 5-year history of intermittent abdominal pain, nausea, and vomiting was transferred to our tertiary-care hospital for acute worsening of symptoms along with clinical signs of obstructive jaundice. A cholestatic pattern of liver enzyme elevation was noted (T. Bilirubin - 2.9 mg/dL, alkaline phosphatase - 293 U/L). Initial abdominal computed tomography revealed a saccular cystic lesion in the caudate lobe of the liver, along with mild intrahepatic ductal dilation, secondary to a focal obstruction/stricture of the common hepatic duct as seen on magnetic resonance cholangiopancreatography. A presumptive diagnosis of a possible congenital anomaly was being considered. Endoscopic ultrasound/endoscopic retrograde cholangiopancreatography with cholangioscopy was performed, demonstrating a soft tissue mass in the common hepatic duct and prominent blood vessels, worrisome for a neoplastic process. Pathology taken from cholangioscopy confirmed a low-grade mucinous cystic neoplasm. Ultimately, the patient underwent a robotic extrahepatic biliary resection, liver resection, and a Roux-en-Y hepaticojejunostomy. Histopathology revealed a mucinous cyst lined by columnar epithelium overlying estrogen receptor-positive ovarian-type stroma, consistent with a low-grade mucinous cystic neoplasms (MCN); no invasive carcinoma was identified. Discussion: Due to insufficient recognition and the absence of distinct clinical and radiological features, MCN-Ls are often misdiagnosed, resulting in a delay in treatment. Evaluation of a multi-loculated hepatic cyst in a woman patient should begin with high-resolution imaging, supplemented with tumor markers, cholangioscopy for tissue acquisition, and definitive intraductal characterization. A review of 22 adult cases (2015–2025) found that all recurrences followed non-curative procedures, while patients undergoing primary margin-negative resection remained disease-free. These findings underscore that definitive treatment requires formal anatomic hepatectomy with concomitant bile duct resection when indicated, with long-term outcomes determined by surgical adequacy rather than tumor biology.