Answer: Adenomyomatous hyperplasia (diffuse adenomyosis)

Histology: In this particular case, the gross description of diffuse gall bladder involvement is more important than the microscopic findings. According to the extent of involvement, adenomyomatous hyperplasia is divided into local, segmental and diffuse forms. The localized form is more commonly known as adenomyoma, and is usually found at the tip of the fundus as a well circumscribed nodule bulging into the lumen or projecting towards the serosal surface. In segmental and diffuse forms, there is a thickening of part, or all, of the gall bladder wall, with predominance of intramural small, cystic spaces.

Discussion: The differential diagnosis is rather straight forward. Rokitansky-Aschoff sinuses are epithelial invaginations that penetrate the muscle layer, and reach the perimuscular connective tissue, and are analogous to diverticula that develop in other hollow organs. In contrast, in adenomyomatous hyperplasia the muscle layer is hyperplastic in contrast to the usual finding in Rokitansky-Aschoff sinuses. Although the smooth muscle hyperplasia and intramural glands seen in a diffuse adenomyomatous hyperplasia of the gallbladder seem somewhat analogous to the smooth muscle hyperplasia seen in uterine adenomyosis, there is no evidence to suggest that diffuse adenomyomatous hyperplasia is a form of endometriosis. Endometrial stroma is not present in the gall bladder in cases of adenomyoma or diffuse adenomyomatous hyperplasia. The histologic features of the glands and the cells themselves should not suggest a diagnosis of carcinoma. Rarely, cases of carcinoma have arisen in the setting of diffuse adenomyomatous hyperplasia, but there does not seem to be any specific relationship between those two disorders. In the literature, adenomyomatous hyperplasia of the gall bladder sometimes appears under the rather interesting name of “hyperplastic cholecytosis.”