Benign Multicystic Peritoneal Mesothelioma Presenting as a Colonic Mass.

Benign multicystic peritoneal mesothelioma (BMPM) is a rare neoplasm of the abdominal mesothelium (i.e., peritoneum, mesentery, and omentum). We present the case of a 74-year-old male who presented with a right paracolic gutter fluid collection and cystic mass. The patient underwent diagnostic laparoscopy with resection of the mass. The final pathology revealed BMPM. The pathogenesis may have been related to longstanding diverticular disease, which could prove to be an underrecognized risk factor for the development of BMPM. Therefore, this case suggests a broadened differential diagnosis to include BMPM in specific cases of pre-operatively diagnosed colonic masses. The patient is disease-free 11 months post-operatively.