Intracystic papillary neoplasm with an associated mucinous adenocarcinoma arising in Rokitansky-Aschoff sinus of the gallbladder.

Intraepithelial neoplasias are preinvasive neoplastic lesions found throughout in the digestive system, and when such lesions are discovered in the gallbladder, they are referred to as intracystic papillary neoplasm (ICPN). In the gallbladder, mucinous adenocarcinoma is a rare histologic phenotype, and adenocarcinomas involving Rokitansky–Aschoff (RA) sinuses are uncommon, which were indeed found in a case reported here. A 64-year-old male presenting with upper abdominal pain demonstrated a spherical mass protruding outward from the gallbladder fundus in imaging studies. Laparoscopic cholecystectomy was performed, and the resected specimen revealed a subserosal cystic mass with a small communication with the gallbladder lumen. The cystic mass contained a gelatinous material without solid component. Histologically, the mass was consisted of subserosal cysts lined by atypical columnar mucinous epithelium with micropapillary growth and nuclear stratification. The neoplastic transformation was more pronounced toward the serosal side of the lesion where disruption of the cyst wall, intrastromal mucin lakes, and invasion of the neoplastic cells into surrounding stroma were observed. The epithelium was of intestinal lineage, which was supported by the positive immunoreactivity against CDX2 and MUC2. The cystic spaces were communicated with surrounding RA sinuses, which indicated that the tumor arose in the sinus. The pathological diagnosis was ICPN, intestinal type, with an associated mucinous adenocarcinoma arising in RA sinus.