Background: Congenital perineal lipoma is extremely rare and may lead to a misdiagnosis of ambiguous genitalia.
Case reports: We report on two girls referred to our service for ambiguous genitalia. Patient 1 (17 days old) and patient 2 (2 months old) had unremarkable gestational and perinatal histories. Both had normal female external genitalia and a 46,XX karyotype. Patient 1 had a polypoid, protruding 3.0 x 2.0 x 1.5-cm phallic-like mass arising at the inferior border of the left labium majora, and patient 2 had a similar mass of 1.5 x 1.5 x 1.0 cm at the same site and an imperforate anus. In both cases the mass was removed and found to be a lipoma.
Discussion: To our knowledge, perineal lipoma has been reported only in eleven girls, nine of them with associated anorectal malformation. Migration and fusion of the labioscrotal folds and formation of the urorectal septum are simultaneous developmental events occurring in the same region, which may explain the association of perineal lipoma and anorectal malformations.