Ultrasonic microdissection of immature intermediate human placental villi as studied by scanning electron microscopy.

The human placenta during the first 20 weeks of gestation undergoes rapid and extensive morphological changes. Near the end of this period, the most predominant type of villus present is the immature intermediate placental villus. In order to visualize this complex structure with scanning electron microscopy (SEM), we have developed a microdissection technique to expose tissue components of the placental villus while retaining its normal histological architecture. Placental villi were initially fixed in Karnovsky's fixative, buffered formalin, or 2% osmium tetroxide solution prior to exposure to connective tissue enzymes or detergents alone or in combination. Samples were dehydrated through 100% acetone and ultrasonicated at 80 kHz for 15 minutes prior to critical point drying and SEM examination. The most satisfactory microdissections were obtained by using a combined detergent/ultrasonication technique. By means of this procedure it was possible to remove the syncytiotrophoblast to expose the underlying cytotrophoblast, basal lamina and the stromal core components of the villi. The selective removal of these structures revealed the 3-dimensional relationships of the stromal channels, reticulum cells and Hofbauer cells. Of interest was the pattern of fetal capillaries coursing parallel to the long axis of each villus and terminating in a vascular knot at the tip.