Intracholecystic papillary neoplasm misdiagnosed as adenomyomatosis on imaging: a case report.

Intracholecystic papillary neoplasm (ICPN) is a rare preinvasive neoplasm of the gallbladder. The lesion typically appears as a polypoid lesion or gallbladder wall thickening. We report a case involving a 40-year-old man with an ICPN that lacked typical polypoid lesions and was difficult to differentiate from adenomyomatosis because of the presence of intramural cysts. Initial contrast-enhanced computed tomography and magnetic resonance imaging showed edematous gallbladder wall thickening. The lumen was constricted and surrounded by a cluster of small cysts that were suspected to be Rokitansky-Aschoff sinuses (RAS). There were also large cysts within the gallbladder wall. No mucosal irregularities or polypoid lesions were observed, and the mucosal continuity was preserved. After antimicrobial therapy, follow-up computed tomography revealed improvement in the thickening of the gallbladder wall; however, the cysts persisted and some had enlarged. The patient underwent laparoscopic cholecystectomy. Pathologically, a tubulopapillary lesion with atypical epithelial cells was observed in the lumen of the gallbladder, extending continuously into the RAS and cysts within the gallbladder wall. High-grade dysplasia was occasionally found, and microscopic foci of invasion were present. ICPN with associated invasive carcinoma was diagnosed. In conclusion, ICPN may not exhibit polypoid lesions or significant wall thickening on imaging. ICPN may present with secondary RAS dilatation, and the presence of large intramural cysts may be helpful in the diagnosis.