Tumors of the appendix: I. Neoplastic and nonneoplastic mucoceles.

We reviewed the clinical data and pathologic material on 46 patients with lesions originally interpreted as appendiceal mucocele or mucinous adenocarcinoma from two medical centers. The mucoceles, characterized by accumulation of mucus in a dilated lumen, could be divided into three distinct entities: nonneoplastic retention mucoceles (eight cases), cystadenomas (26 cases), and cystadenocarcinomas (eight cases). There were four mucinous adenocarcinomas. Retention mucoceles are associated with little morbidity and are cured by appendectomy. Cystadenomas and cystadenocarcinomas mimic the behavior of ovarian neoplasms of borderline malignant potential. Some of these lesions were associated with pseudomyxoma peritonei, but did not have systemic metastases. Mucinous adenocarcinomas without mucocele mimic the behavior of ordinary large bowel carcinoma.