Two-dimensional morphology of a three-dimensional organ

Histopathology of the human placenta is mostly based on the light-microscopical evaluation of paraffin sections. Therefore, the three-dimensional features of normal and pathological placental villi are usually described in terms of the two-dimensional description analysed by light microscopy. Remarkably, the two-dimensional findings often do not reflect the underlying three-dimensional characteristics of villi. This is particularly true when nuclear accumulations (syncytial sprouts, knots, bridges, Tenney–Parker changes) are involved which partly represent true sprouts, knots and bridges (Figure 10.1a,b); however, more often are the result of trophoblastic flat sectioning (Figure 10.1c) (Burton 1986a, b; Cantle et al., 1987; Kaufmann et al., 1987; Kuestermann, 1981).

The histological features of syncytial knotting have different origins

Historically, fungus-shaped, multinucleated protrusions of placental villous surfaces have been interpreted as (a) signs of villous sprouting (Boyd and Hamilton, 1970), as well as (b) signs of nuclear aging (Schiebler and Kaufmann, 1969; Martin and Spicer, 1973) and nuclear shedding (Ikle, 1964).

However, the interpretation became more difficult when it was reported that the multinucleated knots, sprouts and bridges found in two-dimensional paraffin sections very often did not reflect the three-dimensional characteristics of the structures that had been cut. In 1981 Kuestermann used serial paraffin sections to reconstruct the villous tree and found that the seeming sprouts and bridges are mostly flat sections of branches of the villous tree. Similar results were obtained by Burton (1986a, b, 1987) using plastic serial sections and by Cantle et al. (1987) and Kaufmann et al. (1987) using plastic sections of villi which were previously studied by scanning electron microscopy.