Higher magnification of the previous image showing mucinous epithelium lining the villi. Note the striking resemblance to the villous adenomas of the colon. Mucinous cystadenomas of the appendix may be associated with similar lesions of the ovary as well as benign and malignant lesions of the colon. The ovarian and appendiceal tumors are usually synchronous. The ovarian tumors are usually right-sided; a small percentage of cases may have bilateral ovarian tumors. Pseudomyxoma peritonei is often present in such cases. The ovarian tumors are thought to be metastasis/implants from the appendiceal primary.