Introduction: Although both appendiceal tumor and intestinal endometriosis have been reported as rare causes of abdominal pain, the coexistence of appendiceal mucinous neoplasm and ileal endometriosis has not previously been reported.
Case presentation: A 41-year-old Japanese woman presented with a positive fecal occult blood test and a 3-year history of menstruation-related lower abdominal pain. A colonoscopy demonstrated extrinsic compression of the cecum, suggesting a mass arising from the appendix or adjacent structures. Abdominal imaging showed a 6-cm cystic mass with intraluminal thick fluids originating from the appendix. At ileocecal resection for an appendiceal tumor, a 2-cm mass in the terminal ileum was incidentally found, which was included in the surgical specimen. Microscopic examination confirmed a diagnosis of a mucinous neoplasm of the appendix with endometriosis of the terminal ileum.
Conclusions: To avoid urgent surgery for subsequent serious events associated with disease progression, appendiceal tumor and intestinal endometriosis should be ruled out in patients with chronic abdominal pain.