The coexistence of low-grade mucinous neoplasms of the appendix and appendiceal diverticula: A possible role in the pathogenesis of pseudomyxoma peritonei

We examined 38 appendectomies with diagnoses of mucocele, diverticulum, or adenoma to study the coincidence of appendiceal diverticula and appendiceal low-grade mucinous neoplasms and to examine the possible role of diverticu la in the pathogenesis of pseudomyxoma peritonei, Invasive adenocarcinomas and retention cysts were excluded (six cases). Cases were classified as ade nomas or mucinous tumors of unknown malignant potential, with or without di verticula, Medical records were reviewed for multiple parameters, including presenting symptoms, presence of pseudomyxoma peritonei, and presence of a ssociated malignancies, Binomial statistics were used to calculate the prob ability that the observed prevalence of low-grade mucinous neoplasms and di verticula together was significantly different from the expected prevalence of diverticula or low-grade mucinous neoplasms alone, using historical con trols from the literature. Twenty-five percent of the total cases (8 of 32) contained both a low-grade mucinous neoplasm (7 cystadenomas and 1 mucinous tumor of unknown malignan t potential) and a diverticulum, Thus, 8 of 19 low-grade mucinous neoplasms (42%) were associated with diverticula, Of the appendices with both lo rv- grade mucinous neoplasms and diverticula, three contained dissecting acellu lar mucin within the appendiceal wall, four showed diverticular perforation , and one had pseudomyxoma peritonei associated with the ruptured diverticu lum, A significant percentage (P < .001) of cases contained low-grade mucinous n eoplasms and diverticula together. The case of coexistent low-grade mucinou s neoplasm, diverticulum, and pseudomyxoma peritonei suggests that divertic ula could play a role in the pathogenesis of pseudomyxoma peritonei, This c ould occur either by involvement of preexisting diverticula by the neoplasm or by distention of the appendiceal lumen by mucin, leading to increased i ntraluminal pressure and subsequent diverticulum formation at a weak area i n the wall. Either mechanism might allow low-grade mucinous neoplasms to pe netrate the appendiceal wall more easily.