The Coexistence of Low-Grade Mucinous Neoplasms of the Appendix and Appendiceal Diverticula: A Possible Role in the Pathogenesis of Pseudomyxoma Peritonei

Abstract

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 diverticula in the pathogenesis of pseudomyxoma peritonei. Invasive adenocarcinomas and retention cysts were excluded (six cases). Cases were classified as adenomas or mucinous tumors of unknown malignant potential, with or without diverticula. Medical records were reviewed for multiple parameters, including presenting symptoms, presence of pseudomyxoma peritonei, and presence of associated malignancies. Binomial statistics were used to calculate the probability that the observed prevalence of low-grade mucinous neoplasms and diverticula together was significantly different from the expected prevalence of diverticula or low-grade mucinous neoplasms alone, using historical controls 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 malignant potential) and a diverticulum. Thus, 8 of 19 low-grade mucinous neoplasms (42%) were associated with diverticula. Of the appendices with both low-grade mucinous neoplasms and diverticula, three contained dissecting acellular mucin within the appendiceal wall, four showed diverticular perforation, and one had pseudomyxoma peritonei associated with the ruptured diverticulum.A significant percentage (P < .001) of cases contained low-grade mucinous neoplasms and diverticula together. The case of coexistent low-grade mucinous neoplasm, diverticulum, and pseudomyxoma peritonei suggests that diverticula could play a role in the pathogenesis of pseudomyxoma peritonei. This could occur either by involvement of preexisting diverticula by the neoplasm or by distention of the appendiceal lumen by mucin, leading to increased intraluminal pressure and subsequent diverticulum formation at a weak area in the wall. Either mechanism might allow low-grade mucinous neoplasms to penetrate the appendiceal wall more easily. KEY WORDS

The relationship between diverticula and low-grade mucinous neoplasm of the appendix. Does the diverticulum play a role in the development of periappendicular mucin deposition or pseudomyxoma peritonei?

“…However, the number of cases that were followed-up are few and the follow-up periods are short. In the study by Lamps et al, rupture of the diverticulum was correlated with pseudomyxoma peritonei in only one case [20]. No comment was made about the relationship between rupture of the diverticulum and periappendicular mucin without epithelium in other studies.…”

“…They suggested that diverticula may give a clue about underlying neoplasms [16]. In the study by Lamps et al diverticula were determined in 8 of 19 LGMNs (42%) [20]. We detected accompanying diverticula in 23 of 38 LGMN cases (60.5%).…”

“…However, no accumulation of mucin was seen on serosal surface or mesoappendix [20]. Mucin accumulation was determined on appendix, gallbladder, omentum, and serosal surface of bowels with ruptured diverticulum during appendectomy in only one out of eight cases [20]. In our 13 cases, which had mucin accumulation on mesoappendix, and were followed-up between eight months and seven years, pseudomyxoma peritonei did not develop.…”

“…In the study of Lamps et al acellular mucin accumulation was detected around inflamed, perforated diverticulum in the wall of the appendix in three out of eight LGMN cases. However, no accumulation of mucin was seen on serosal surface or mesoappendix [20]. Mucin accumulation was determined on appendix, gallbladder, omentum, and serosal surface of bowels with ruptured diverticulum during appendectomy in only one out of eight cases [20].…”

“…3, 4, 5, 6). Twelve of 20 LGMN cases (60%), which were specifically sampled cases between 2011 and 2015, were accompanied by diverticulum. Ninety-six diverticula were determined in 1902 cases without LGMN, and the prevalence was 5.04%.…”