PART TWO
Diagnostic Cytology
The Normal Uterine Cervix
Histology and Cytology
Ectocervix
The vagina and the outer portion of the uterine cervix—the
ectocervix—are lined with nonkeratinizing squamous epithe-
lium. Embryologically, this epithelium is derived from a solid
epithelial plate growing inward from the urogenital sinus up to
the level of the later endocervical canal. This solid plate replaces,
at the level of the vagina and the ectocervix, the primitive cuboi-
dal epithelium from the fused Mullerian ducts, from which also
originates the columnar epithelium, lining the fallopian ducts,
the uterine corpus, and the endocervical part of the cervix. The
fusion site of these two types of epithelium is called the
squamo-
columnar junction
(Fig. 8.1). The location of this fusion site varies
considerably, depending on physiologic and pathologic condi-
tions. During reproductive years, the squamocolumnar junction
is located at the entrance of the endocervical canal, the
external os,
but owing to hormonal influences or as a result of stromal
edema that has changed the endocervical canal or cervix, it may
be located inside the endocervical canal or on the surface of the
cervix. When located on the external surface of the cervix, part
of the columnar cell lining of the endocervical canal is present
on the ectocervical face. This causes a usually well-demarcated
reddening of the surface that is easily recognizable at inspection.
This outward bulging of the endocervical mucosa, referred to as
ectropion, eversion,
or
false erosion,
should be differentiated from a
true erosion
of the epithelium, which by definition is a loss of the
lining mucosa, leaving the underlying cervical stroma barren.
During childhood and after menopause, the squamocolumnar
junction is located inside the canal.
During reproductive years, the morphology of the strati-
fied squamous epithelium, the function of which is primarily
a protective one, is cyclically changing under the influence of
ovarian hormones. In its fully matured stage, the epithelium of
the vagina and ectocervix can be subdivided into several layers
(Fig. 8.2). For correlation with the different cell types present
in cervical cytologic specimens, a subdivision into three layers
is most practical. Beginning with the deepest layer, these are
Fig. 8.1 Squamocolumnar junction.
Fusion site of the stratified
nonkeratinizing squamous epithelium of the ectocervix and the mucus-
producing columnar epithelium lining the endocervical canal (H&E x HP).
the (1) basal cell and parabasal cell layer, (2) intermediate cell
layer, and (3) superficial cell layer. Under physiologic condi-
tions, epithelial regeneration takes place in the basal layer, usu-
ally composed of a single layer of relatively primitive cells with
scarce cytoplasm and large oval-to-round nuclei with promi-
nent nucleoli. Under normal conditions, true basal cells are not
present in cervical smears unless, when the smear is taken, the
entire epithelial layer has been removed, leaving the underly-
ing stroma denuded. Parabasal cells are unusual in smears from
women in reproductive years, unless certain pathologic proc-
esses, particularly a reduced or absent estrogenic hormonal
stimulation, occur. They are the predominant cell type in smears
from women in postmenopause and from children.
Parabasal cells are round to oval and have a small cytoplasmic
body and relatively large oval-to-round nuclei (Fig. 8.3; see also
Fig. 8.16). The cytoplasm is relatively dense, has distinct bor-
ders, may contain vacuoles, and commonly stains cyanophilic.
After drying of the vaginal or cervical surface due to absence of
estrogenic stimulation or after exposure to air, the cytoplasm
stains eosinophilic.
The major part of the thickness of the epithelium is formed by
the intermediate cell layer. With maturation of the cells toward
the surface, the cells become better differentiated, reflected by
Fig. 8.2 Normal mature stratified nonkeratinizing squamous
epithelium,
covering the ectocervical surface (H&E x HP).
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