Sirenomelia ('mermaid').

A case of sireniform malformation in a 17-wk-old fetus is described. In addition to the characteristic fusion of the lower limbs, there were also severe malformations of the urogenital system and lower intestinal tract. The essential features and various theories of genesis are discussed. The cases so far described in literature are reviewed. Ultrasound can be very useful in early detection of this deformity, because defective movements of the single lower limb and the typical medial position of the fibulae can be seen.