Fetal diagnosis of penoscrotal transposition associated with perineal lipoma in one twin.

Perineal lipoma is a rare condition which is commonly associated with scrotal anomalies and may be diagnosed as ambiguous genitalia. We report on a baby with penoscrotal transposition (PST) consisting of bifid scrotum and hypospadias with chordee associated with perineal lipoma. The affected baby was one twin of an IVF pregnancy referred to our center for ambiguous genitalia by fetal ultrasound. Examination of the uterus revealed a dichorionic, diamniotic twin pregnancy. Fetal ultrasound and MRI in our center revealed an exophytic perineal mass, which likely represented a lipoma, separate from the abnormally appearing phallus and scrotum (hypospadias with chordee and a bifid scrotum). This likely fell into the PST spectrum. There were no additional abnormalities in the other structures and no structural abnormality of co-twin was detected. Fetal growth of both twins was appropriate for gestational age. Babies were born at term and the findings of the affected twin correlated with the fetal diagnoses. While some reports show PSTs are associated with multiple anomalies, in this case no additional anomalies were identified. Perineal lipomas are commonly associated with scrotal abnormalities and anorectal malformations. It is hypothesized that these anomalies develop because of the perineal lipoma. MRI combined with ultrasound clearly defined the anomaly prenatally and allowed for accurate prenatal counseling and coordination of postnatal care.