The evaluation of 73 appendiceal lesions fulfilling the criteria of so‐called “mucocele” showed that they comprise 3. distinctive clinicopathologic entities: 1) Focal or diffuse mucosal hyperplasia, with no epithelial atypia and mild distention of the lumen (18 cases). The microscopic pattern is highly reminiscent of the colonic hyperplastic polyp. This is a benign lesion, almost always a pathologic finding in appendices removed incidentally. Of the 18 cases classified as such, 5 were associated with adenocarcinoma of the large bowel, and 1 with ovarian mucinous cystoma; 2) Mutinous cystadenoma, exhibiting some degree of epithelial atypia and marked distention of the lumen (46 cases). Four of these were associated with ovarian mucinous cystoma and 9 with adenocarcinoma of the large bowel. In 10 cases, variable amounts of acellular mucus were present in the periappendiceal region and occasionally free in the peritoneal cavity. In 3 of these cases the mucus most probably originated from a coexistent ovarian tumor. Of the followed patients, none died as a consequence of the appendiceal cystadenoma. Simple excision of the lesion was curative in every case; and 3) Mucinous cystadenocarcinoma (9 cases). This group was distinguished from the previous one by the presence of stromal invasion by glands and/or epithelial cells in the peritoneal implants. Six were associated with peritoneal involvement (so‐called pseudomyxoma peritonei); in 2 others, the lesion was limited to the appendix, and in the remainder there was direct extension into the urinary bladder. Of the 6 patients with peritoneal extension, 4 died as a result of the disease 2‐11 years after the original surgery, 1 was lost to followup, and the sixth case is a recent observation. The 2 patients with localized tumor were alive and well 2 and 19 years after treatment, respectively. The patient with direct extension into the urinary bladder was alive and well 7 years after an anterior pelvic exenteration. On the basis of these findings we suggest that most instances of so‐called “mucocele” should be regarded as mucinous neoplasms, analogous in many aspects to the epithelial tumors of the colon, with peculiarities probably due to the anatomical characteristics of the organ in which they arise.
