Diffuse deciduosis occurring within an ovarian cystadenoma – a clinical–pathological mimic of a malignant process

Deciduosis is a term referred to foci of ectopic decidualized stromal cells thought to be due to a form of “stromal mullerianosis”. The changes are commonly observed in association with pregnancy and are sometimes secondary to exogenous progesterone administration. Deciduosis of various sites have been reported, some of which include the peritoneal surfaces of pelvic and abdominal structures. Deciduosis is usually an incidental finding at caesarean section and runs an asymptomatic benign course, though some articles have reported rarer cases associated with potentially fatal haemoperitoneum, dystocia, and even symptoms mimicking acute bowel obstruction. Although not always clinically significant, deciduosis can prove a difficult diagnostic dilemma clinically and on histopathology as a result of its pseudomalignant morphological appearance.