ABSTRACT
Histopathologic lesions of the placenta can be categorized by pathogenic mechanism (e.g. placental bed underperfusion) and by type of underlying maternal disorder (e.g. diabetes mellitus, heritable thrombophilias, metabolic diseases). However, pathologists are often faced with the task of evaluating placentas without the benefit of much accompanying clinical history. Therefore, we have chosen to adopt the categorization by site (Table 8) and, secondarily, to list the differential diagnoses of these lesions, in overview. Use of this histologic scheme, however, is predicated on: first, basic knowledge of the normal maturational gross and microscopic changes that occur during gestation (as described in Chapter 2 and amplified below); and second, appreciation of the fact that the gross and microscopic features seen at the time of pathologic examination represent a point of ‘arrest’ in the continuum of placental development in the given case. Hence, any gross or microscopic assessment of a placental specimen should be made with reference to the features normally expected for the gestational period in question and to maternal and fetal disease processes, abnormalities occurring during labor and delivery, and primary placental abnormalities. Some features, such as syncytiotrophoblastic knots (see below) for example, are normally present at term, but pathologic when present early in gestation or when relatively increased in numbers in late gestation. The structures of normal villous types and highlights of normal villous development are shown in Figure 38.
