[The fetus without a heart: the diagnosis and observations using ultrasound. A case history].

The condition is extremely rare, since acardia is only found in 1% of monozygotic twin pregnancies. A case was discovered and observed using ultrasound and was then studied anatomically and pathologically. The histopathology and the physiopathology of the malformation is described. The aetiology that has been most usually accepted is that there is an anastomosis between the two umbilical cords of the two "twins" and that this leads to an inversion of the direction of the circulation in the affected fetus. The failure of the myocardium to develop would follow this vascular abnormality because of failure of the allantoid vessels to fuse. The interest in this kind of observation lies in the possibility of making the diagnosis very early in pregnancy using ultrasound, and of following the evolution and the regression of the acardiac fetus throughout the pregnancy, and with the possibility of comparing the views obtained by ultrasound with the anatomo-pathological features that can be diagnosed after birth.