Low-grade appendiceal mucinous neoplasm and endometriosis of the appendix.

Background: A distended, mucous-filled appendix is known as an appendiceal mucocele. They are a rare form of an appendiceal mass and develop from both benign and malignant processes. Mucoceles can develop secondarily to an obstruction, such as from a fecalith, scarring or, rarely, endometriosis. Only 12 cases of non-neoplastic appendiceal mucoceles caused by endometriosis have been previously described. The association between neoplastic appendiceal mucoceles in the presence of endometriosis is described for the first time in this report.

Case Presentation: A 57-year-old woman presented with a chief complaint of worsening abdominal pain over the past 3 months. Imaging studies revealed an appendiceal mass. Laparoscopic evaluation confirmed an appendiceal mucocele, and the patient underwent complete appendectomy. No evidence of mucinous or endometrial deposits were present within the abdominal cavity. Pathological diagnosis revealed low-grade appendiceal mucinous neoplasm (LAMN) with evidence of endometriosis within the muscularis propria of the appendix. The patient recovered without complications and her abdominal pain completely resolved.

Conclusions: Endometriosis of the appendix is a rare manifestation and is most often identified as an incidental finding. Endometriosis leading to an obstructive mucocele of the appendix is an exceedingly rare finding, having only been described 12 times in the medical literature. LAMN in the presence of endometriosis of the appendix is described for the first time in this report. The association between appendiceal neoplasms in the presence of endometriosis requires further research in order to optimize operative treatment.