8
Benign Proliferative Reactions, Intraepithelial Neoplasia, and Invasive cancer of the Uterine cervix
Fig. 8.30 Immature squamous metaplasia.
Epithelial lining composed
of relatively mature squamous metaplastic cells. In the superficial layers,
maturation is still incomplete, resulting in cells with relatively high
nucleocytoplasmic ratios. Cytoplasmic borders are distinct. A small island
of columnar cells is recognizable in the superficial layer (H&E x MP).
immature squamous metaplasia changes often demonstrate
some degree of atypia. Cells and nuclei show a slight irregu-
larity in size and shape, which is understandable because most
metaplastic changes occur under the influence of some irritating
factor (Fig. 8.30; see also Fig. 8.29). Differential diagnosis with
dysplastic changes should be made on the basis of the evenly
distributed, finely granular, nonhyperchromatic chromatin.
Key features of immature squamous metaplasia
• Cells in sheet-like aggregates with usually distinct cell
borders;
• Densely cyanophilic cytoplasm;
• Relatively large round-to-oval nuclei;
• Increased nucleus-to-cytoplasmic ratio;
• Finely granular, evenly distributed normochromatic
chromatin;
• Conspicuous micronucleoli; and
• Macronucleoli sometimes present.
Mature Squamous Metaplasia
Squamous metaplasia is represented by a spectrum of epithelial
changes resulting in an admixture of cells of varying maturity in
the cellular sample.
The
squamocolumnar junction
bears no constant relation-
ship to the anatomic external os, and the external os has no
histologic landmarks to delineate it. The increase in linear
extent of squamous metaplasia in the endocervical canal and
the region of the transformation zone with increasing age is
inversely related to the reduction of the linear extent of reserve
cell hyperplasia.
Mature
squamous
epithelium
encompasses
the
clas-
sic three layers of nonkeratinizing squamous epithelium,
making mature squamous metaplastic epithelium virtually
indistinguishable from the original ectocervical squamous
epithelium. Foci of mature squamous metaplasia may be
indistinguishable from the normal ectocervical mucosa. The
only clue to its metaplastic origin is underlying endocervical
glands (Fig. 8.31).
Fig. 8.31 Mature squamous metaplasia.
An island of mature squamous
metaplastic epithelium bordered by endocervical columnar epithelium.
Mature squamous metaplastic epithelium has great resemblance to
stratified squamous epithelium of the ectocervix (H&E x MP).
The presence of squamous metaplasia in cervical smears was
reported by von Haam and Old to be 41.5%.16 Howard and
co-workers reported an 83% incidence,17 and Carmichael and
Jeaffreson found it to be present in 41% of cervices examined
histologically.18
The relationship of age to prevalence of squamous metapla-
sia was found by von Haam and Old to be 86.2% in the third
decade of life and 69.2% in women older than 60 years.16 In
101,000
first cervical smears from women 35 to 54 years of age,
62.5% contained squamous metaplastic cells. The prevalence of
squamous metaplasia rises significantly from the third to the
fifth decade.19
Cytology
Cells originating from squamous metaplasia tend to be isolated,
less frequently occurring in loose sheets. The number of cells
varies with the extent of the epithelial change, the localization of
the lesion, and the method of sampling.12,13 Cells from squamous
metaplasia characteristically have distinct borders and are pre-
dominantly round, oval, or polyhedral. In immature squamous
metaplasia, the cytoplasm is homogeneous and cyanophilic,
whereas in a more mature type of metaplasia, it is characterized
by a more densely staining outer zone or ectoplasm and a clear
central perinuclear zone or endoplasm (Fig. 8.32). At the periph-
ery of the cells, remnants of the fibrillar apparatus, observed in
normal squamous cells, may be demonstrated. The nuclei are
relatively small, round or oval, usually centrally located, and
uniform in size and have a basically finely granular chromatin
in which there are small aggregates or chromocenters.14 Mature
squamous metaplastic cells can sometimes be differentiated
from cells derived from the original ectocervical squamous
epithelium by their slightly denser staining cytoplasm.
Key features of mature squamous metaplasia
• Cells tend to be isolated or less frequently in loosely
aggregated sheets;
• Cytoplasmic borders are distinct;
• Cells are round to oval, or polyhedral;
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