[Vulvar mass in neonatal period : spot the difference].

We report the cases of two female newborns who present, at the first day, a interlabial mass. In both cases, the antenatal scans were normal, and the clinical examination in the delivery room didn't reveal any other abnormality. Similar features may suggest the same diagnosis. However, in the first case, it is a paraurethral cyst which causes the bulging of vaginal introitus whereas, in the second infant, it is an imperforated hymen. Paraurethral cysts are uncommon and even more so among infants. The diagnosis is primarily clinical, and ultrasound confirms the diagnosis and verifies the absence of other associated anomalies. These cysts usually resolve spontaneously. Rarely, they can lead to urinary retention. The second diagnosis, imperforate hymen, is the most common congenital malformation of the female genital tract. It can lead to hydrocolpos with the upstream accumulation of vaginal secretion and sometimes induce a hydrometrocolpos, with vaginal and uterine dilatation. The resulting mass can cause obstruction of surrounding urinary or digestive structures. Surgical management is generally necessary.