MUC5AC and adenoma: Most appendiceal mucoceles are caused by epithelial lesions associated with mucin production, such as hyperplastic polyps, adenomas, and carcinomas.[5] A minority of appendiceal mucoceles are caused by retention of mucin secondary to obstruction or stenosis of the appendix due to fecaliths, post-inflammatory scarring, and rarely are they caused by endometriosis (called obstructive, retention, and simple mucoceles).[5] Endometriosis is a common disease in women, defined as functioning endometrial tissue in a location outside of the uterus.