A condition characterized by poorly-circumscribed gelatinous masses filled with malignant mucin-secreting cells. Forty-five percent of pseudomyxomas arise from the ovary, usually in a mucinous cystadenocarcinoma (cystadenocarcinoma, mucinous), which has prognostic significance. pseudomyxoma peritonei must be differentiated from mucinous spillage into the peritoneum by a benign mucocele of the appendix. (Segen, dictionary of Modern medicine, 1992)