Answer: Lymphoma

Histology: The gallbladder shows the typical features of chronic cholecystitis, in that there is thickening of the muscular wall and Rokitansky-Aschoff sinuses. There is a chronic inflammatory infiltrate, which is usually mild in stone associated cholecystitis. However, on closer inspection of the inflammatory infiltrate, the lymphocytes are monotonous and are frequently unassociated with the epithelium of the gallbladder. This suggests that the lymphocytes are not reacting to a mucosal stimulus and instead may be neoplastic.

This patient proved to mantle cell lymphoma and these lymphocytes were diffusely reactive for cyclin D1 in a nuclear fashion, confirming involvement of the gallbladder by mantle cell lymphoma.

Discussion: As mentioned above, stone associated chronic cholecystitis usually does not demonstrate a prominent lymphoid infiltrate. The lymphocytes, when present, are polymorphous. Follicular cholecystitis would require the presence of reactive lymphoid follicles centered on the mucosa of the gallbladder. The cholecystitis associated with primary sclerosing cholangitis is non-specific, but is characteristically a superficial diffuse lymphoplasmacytic cholecystitis.