[Incidental finding of a Müllerian cyst in an exceptional retroperitoneal localization].

Mullerian cysts are mostly described in women, near the genitourinary organs. Exceptional cases of retroperitoneal and posterior mediastinal located Mullerian cysts have been reported. When located in the retroperitoneum, those cysts are often confused with other retroperitoneal cysts such as cystic lymphangioma and cystic mesothelioma of peritoneum because of the poor clinical picture and a nonspecific radiologic presentation. The histopathological analysis is essential to make the diagnosis, and the positive staining of a Müllerian marker is a decisive argument in favor of a Müllerian cyst. Here, we report a case of an incidental finding of a retroperitoneal Müllerian cyst in a 68-years-old woman.