Prenatal diagnosis of sirenomelia in the second trimester of pregnancy using two-dimensional ultrasound, three-dimensional ultrasound and magnetic resonance imaging

.The case reported here represents the rarest form of congeni-tal carpal boss, in which the os styloideum is fused to the trap-ezoid, which occurs in only 0.5% of cases. More commonly (in94.0% of cases), it is fused to the base of the second and thirdmetacarpal, merged with the capitate (in 3.5%) or (in 2.0%) iso-lated