Urorectal septum malformation sequence: prenatal sonographic diagnosis in two sets of discordant twins

Urorectal septum malformation sequence (URSMS) is a rare congenital malform ation, which includes ambiguous genitalia, a phallus-like structure, imperf orate anus, bladder vaginal and rectal fistulas and Mullerian duct defects. We report two cases of prenatally diagnosed URSMS, both occurring in two s ets of discordant twins. To the best of our knowledge, this is the first an tenatal description of such an anomaly. The first fetus, one of a set of mo nochorionic, monoamniotic twins was detected sonographically at 21 weeks of gestation due to an enlarged Phallus-like formation. The second fetus, one of dichorionic, diamniotic twins, was suspected of having an abnormally en larged rectum at 13 weeks of gestation. The diagnosis of URSMS was establis hed at 29 weeks of gestation by showing abnormal female external genitalia, with a dilated bowel that contained echogenic foci due to enterolithiasis. The diagnosis of both cases was confirmed Postnatally. Sonographic finding s and differential diagnosis are presented.