Cloaca in discordant monoamniotic twins: prenatal diagnosis and consequence for fetal lung development.

Objective  Describe a case of cloaca prenatally diagnosed in one of a set of monoamniotic twins. Study Design  Retrospective review of a case. Results  Cloaca is one of the most complex and severe degrees of anorectal malformations in girls. We present a discordant cloaca in monoamniotic twins. Fetal ultrasound showed a female fetus with a pelvic midline cystic mass, a phallus-like structure, a probable anorectal atresia with absence of anal dimple and a flat perineum, and renal anomalies. The diagnosis was confirmed by fetal magnetic resonance imaging postnatally. Conclusions  The rarity of the malformation in a monoamniotic pregnancy, the difficulties of prenatal diagnosis, the pathogenic assumptions, and the consequences of adequate amniotic fluid for fetal lung development are discussed.