[Deciduosis of the appendix. Differential diagnosis of acute appendicitis].

Deciduosis of the appendix is a rare cause of acute appendicitis in pregnancy. Ectopic decidual cells localized in the submesothelial stroma may represent a physiologic reaction of the pluripotent stromal cells to progestational hormonal stimulation. Less frequently, deciduosis is based on a preexisting extragenital endometriosis, visible in a localization other than strictly submesothelial, in residuals of cyclic proliferation and bleeding, and in endometrial glandular formations embedded in the decidual cells.