Identification of Signet Ring Cell Change in Colonic Subserosa in the Setting of Clostridium difficile Colitis

Signet ring cell change of intestinal epithelial cells is a rare but well-known mimicker of signet ring cell carcinoma and is often associated with ischemic and/or pseudomembranous colitis. Instead, signet ring cell change involving nonepithelial cells in the subserosa of the intestine is an extremely rare finding with only a single case report in the literature to date. We report a new case of benign signet ring cell change localized in the subserosa of the large bowel incidentally identified in a resection specimen for Clostridium difficile colitis mimicking a metastatic signet ring cell carcinoma. Based on the morphologic features and immunohistochemical profile, we propose that these signet ring cells may possibly represent modified/degenerated fat cells. Furthermore, we discuss how to differentiate benign signet ring cells from a signet ring cell carcinoma.