Descending Repair Figs 1927

Endocervical mucosal surface epithelium that everts out onto the portio may become replaced by squamous epithelium in two ways: (1) by overgrowth from adjacent regenerative ectocervical epithelium, as in ascending repair (Figs. 10-13), or (2) by squamous metaplasia of the reserve cells of the endocervical epithelium, as in descending repair. Both processes may occur simultaneously or separately. In general, ascending repair is stimulated by endogenous or exogenous estrogens, whereas descending repair predominates under endogenous or exogenous gestagenic stimulation (Dallenbach-Hellweg 1981). Descending repair is preceded by a double- or multilayered hyperplasia of the reserve cells (Figs. 19,2o),which,in accordance with their cytokeratin endowment, undergo metaplastic change and differentiate into squamous epithelium (Figs. 21,22). Some of these metaplastic cells, however, may retain their bipotential capacity and produce mucin, thereby being responsible for the monocellular mucin formation occasionally seen in squamous cell metaplasia of the endocervix (Figs. 23,24).

During maturation to squamous cells, their capability to produce mucin is usually lost. In contrast, the squamous epithelium adjacent to the endocervical epithelium expresses cytokeratins of the squamous epithelium type in all layers, whereas the columnar epithelium neighboring it exhibits a positive reaction only in the underlying reserve cell layer (Fig. 25). With mucin stains, a faint positive reaction may be detected in the superficial cell layer, which may include the flattened atrophic remnants of columnar cells that originally covered the reserve cells (Figs. 26,27).

Columnar Cells Differentiation
Fig. 19. Hyperplasia of reserve cells in descending repair. H&E
Reserve Cell Hyperplasia
Fig. 20. Hyperplasia of reserve cells. Immunohistochemical reaction with cytokeratin 13
Cell Differentiation PicturesSquamous Cell Hyperplasia
Fig. 22. Hyperplasia of reserve cells differentiating into squamous metaplasia. Immunohistochemical reaction with cytokeratin 13
Squamous Hyperplasia
Fig. 23. Monocellular mucin formation in squamous metaplasia. H&E
Squamous Metaplasia Endocervix
Fig. 25. Squamocolumnar junction with original squamous epithelium and adjacent reserve cell hyperplasia underneath the columnar epithelium. Immunohistochemical reaction with cytokeratin KA 1 (from Franke et al. 1986)
Squamous Metaplasia Endocervix
Fig. 27. Junction between squamous metaplasia and columnar epithelium.Alcian blue reaction

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