[Decidua in the peritoneal surface mimicking metastatic nodules. Findings during cesarean section]

The occurrence of ectopic decidua has been observed most often in the ovaries, uterus, and cervix. A peritoneal localization is less frequent and usually an asymptomatic incidental finding. Ectopic decidua was investigated in biopsies taken during cesarean sections, elective tubal ligations, appendectomy and in tubal pregnancies. Histologic studies have been carried out of fragments from the epiploon, appendiceal serosa, tubal serosa, retroperitoneal lymph nodes and various abdominal organs. Our purpose is to report a case of peritoneal deciduosis in a 46-year-old woman, asymptomatic, discovered during cesarean section and mimicking metastatic nodules (incidental finding). The histopathological diagnosis was done based on specimen studied with the common technique of paraffin embedding and hematoxilin--eosin staining. We believe that this decidual transformation of the peritoneum arises from a progesterone-induced metaplasia of the coelomic stroma, being often a totally reversible phenomenon.