8
Benign Proliferative Reactions, Intraepithelial Neoplasia, and Invasive cancer of the Uterine cervix
Fig. 8.23 Immature squamous metaplasia.
Under the single layer of
endocervical columnar cells, a layer of immature squamous metaplastic cells
showing slight irregularity in size and shape has been formed. In the vesicular
nuclei are finely granular nonhyperchromatic chromatin and prominent
nucleoli (H&E x HP).
epithelium or may attain a considerable thickness. The prolifera-
tion not only simulates carcinoma in situ but actually may rep-
resent a developmental stage of this process.14 In the cytologic
specimen, cells are usually arranged in the form of a sheet. Cell
borders are often poorly defined, giving the cell aggregates the
appearance of a syncytium but lacking the loss of polarity and the
disorganization usually observed in carcinoma in situ.
Reserve cell hyperplasia represents theoretically the earliest
stage in immature squamous metaplasia in the uterine cervix.
The concept of reserve cell hyperplasia as a stage in squamous
metaplasia based on the embryonic rest hypothesis was initially
proposed by Eichholz.15
Reserve cell hyperplasia is in all instances related to the
endocervical canal.12 The predominant site of pure reserve cell
hyperplasia is in the proximal part of the endocervical canal,
somewhat more proximal than the site of maximal involvement
of immature squamous metaplasia.
A surface reaction with any degree of differentiation toward a
squamous cell type is more logically placed within the category
of immature squamous metaplasia despite the persistence of an
overlying endocervical columnar epithelium.
Fig. 8.24 Immature squamous metaplasia.
Layers of relatively immature
squamous cells beneath endocervical columnar cells (H&E x HP).
Fig. 8.25 Immature squamous metaplasia.
Multiple layers of relatively
mature squamous metaplastic cells have replaced the endocervical columnar
lining (H&E x MP).
Immature Squamous Metaplasia
Immature squamous metaplasia represents the morphologic
spectrum of epithelial changes from a single or multiple layers
of reserve cells to an epithelium composed of three or more lay-
ers of cells with features of mature nonkeratinizing squamous
epithelial cells (Figs 8.23 to 8.25; see also Fig. 8.30). Unlike
reserve cells, cells derived from areas of immature squamous
metaplasia are more often isolated (Figs 8.26 to 8.28). Their
tendency to occur as single cells is correlated with the degree of
maturation of the parent epithelium. The majority of cells are
round to oval, with the number of polygonal cells increasing
with maturation. The cytoplasm of immature squamous meta-
plasia cells is dense, homogeneous but sometimes vacuolated,
and cyanophilic in staining reaction (Fig. 8.29). Cytoplasmic
vacuolation is frequently observed in the presence of inflamma-
tion or as a consequence of degeneration. Nuclei, particularly
in the more immature cells, are large, creating a high nucleo-
cytoplasmic ratio (see Fig. 8.28). In cervical smears, cells from
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