Intracholecystic papillary neoplasm mimicking a submucosal tumor

Intracholecystic papillary neoplasms (ICPN) are a rare type of gallbladder papillary neoplasms. They demonstrate more complex morphological and immunohistochemical features than intraductal papillary mucinous neoplasms or intraductal papillary neoplasms of the bile duct. Moreover, gallbladder tumors sometimes show an irregular appearance owing to Rokitansky-Aschoff sinus (RAS) involvement. Herein, we report a case of ICPN that mimicked a submucosal tumor. An 81-year-old man presented to the emergency department of our hospital with right hypochondralgia. Abdominal ultrasonography revealed a 15 mm × 11 mm × 9 mm-sized intramural mass at the gallbladder fundus, which was similarly detected on T2-weighted magnetic resonance imaging as a multinodular lesion within the thickened wall. The patient underwent laparoscopic cholecystectomy two months after the first symptom onset. Macroscopically, the cholecystectomy specimen showed a thickened wall at the fundus with smooth mucosa. The cut surface revealed multilobulated cysts containing a whitish friable lesion measuring 11 mm × 9 mm accompanied by mucus and hemorrhage. Microscopically, papillary configurations composed of proliferative glandular epithelia with high-grade dysplasia without invasion presented within a dilated RAS. Immunohistochemistry revealed strong positive staining for MUC5AC and Hep Par-1 and focal positive staining for MUC2, CK7, and CD117. The lesion was diagnosed as an ICPN with high-grade intraepithelial neoplasia and an oncocytic phenotype.