Scanning electron microscopy of intervillous connections in the mature human placenta

The appearances of intervillous connections linking villi in the mature human placenta are described using the scanning electron microscope. Whilst the majority passed between adjacent terminal villi, in some cases the interconnections linked terminal and intermediate villi, or even two intermediate villi. Two types of intervillous bridge were observed. Examples of the first type were remarkably consistent in size, being approximately 10-15 microns in diameter, whereas the second type comprised the extremely slender syncytial bridges, only 2-3 microns in diameter. Microvilli covered the surfaces of both types of bridge, and were identical to the microvilli covering the remainder of the villous surface. One important aspect of these villous interconnections is that they may rupture either during delivery of the placenta, or during subsequent tissue processing. Breakage most commonly occurs at the point of attachment of a bridge to the villous surface, and so results in the formation of stalk-like protrusions with discontinuous ends. Equally, areas of syncytial damage are created at the points of prior attachment. These roughly circular areas, 10-15 microns in diameter, should be considered a normal feature of the mature delivered placenta. It is important that anyone examining the placenta microscopically is aware of their occurrence so that if seen in section these areas are not misinterpreted and ascribed a pathological significance.