Deciduosis of the appendix: diagnostic dilemma continues despite MRI evidence

Deciduosis (ectopic or extrauterine decidua) is a phenomenon seen in the ovary and cervix and on serosal surfaces of abdominal and pelvic organs. It is thought to be the result of progesterone effects on extrauterine mesenchymal cells during pregnancy. Although deposits are typically asymptomatic and incidentally found in surgically removed tissues on microscopy, deciduosis has also been known to cause pain and intraperitoneal haemorrhage. We sourced all cases of appendiceal deciduosis that have occurred in Sir Charles Gairdner Hospital and Bunbury Hospital between the years 2006 and 2014. Clinical information was obtained from patients' medical records. Four cases of ectopic decidua of the appendix, all of which were incidentally found in pregnant patients presenting with features highly suggestive of appendicitis, were reviewed. These patients underwent appendicectomy and subsequent histopathology findings showed deciduosis with no evidence of appendicitis. Deciduosis of the appendix can mimic acute appendicitis in pregnancy. At present, it is difficult to confidently differentiate one from the other either by way of clinical presentation or with current imaging modalities.