Answer: Adenomyosis

Histology: The surface gallbladder demonstrated papillary hyperplasia, but lacks cytologic atypism. The worrisome feature of this case is the extension of glands through fibrous tissue adherent to the liver. While these glands have a somewhat infiltrative pattern, their cytology is completely benign, and they have an overall lobular distribution. Additionally, plugs of bile are evident in several of these glands. These features support a benign diagnosis, which is best classified as adenomyosis.

Discussion: Adenocarcinoma of the gallbladder is the key differential diagnosis here. The absence of cytologic atypia and lobular architecture of the deeply penetrating glands supports a benign interpretation. Mucinous cystic neoplasms of the gallbladder have the same ovarian-type stroma as is typical of their pancreatic counterparts. Biliary papillomatosis is a diffuse process affecting the gallbladder, extra- and intrahepatic biliary system. This process does not typically form a mass growing through the wall of the gallbladder.

Rare cases of adenomyosis of the gallbladder may demonstrate perineural invasion, another feature which raises the possibility of carcinoma. While the classic appearance is that of a nodule in the fundus of the gallbladder, occasional lesions grossly manifest themselves as strictures in the gallbladder, or diffuse thickening of the gallbladder wall. The latter two scenarios further raise the concern for malignancy.