Ectopic decidua of the appendix: a case report

BACKGROUND: Ectopic decidua is the presence of decidual tissue outside the uterus. Ectopic decidua of the appendix is a rare entity that can present with abdominal symptoms mimicking appendicitis. We report a case of a 39-year-old female patient at 27 weeks gestational age with a 2-day history of right lower quadrant abdominal pain. CASE PRESENTATION: The patient was referred to our hospital with suspicion of either acute appendicitis or threatened rupture of the uterus, the latter of which was considered unlikely following close examination. Therefore, she underwent emergency appendectomy via laparotomy. Microscopic examination revealed decidual tissue with myxoid degeneration in the subserosal layer of the tip side of the appendix, without endometriosis, which was compatible with ectopic decidua (deciduosis). CONCLUSIONS: Because it is extremely difficult to distinguish ectopic decidua of the appendix from acute appendicitis, even with various imaging modalities, we should be aware that ectopic decidua of the appendix is a differential diagnosis for acute appendicitis in pregnant women.