Fig. 13.20 Reactive alveolar epithelium. The cells possess moderate
Fig. 13.22 Hyperplasia of reserve cells. Bronchial biopsy (H&E x MP).
to abundant vacuolated cytoplasm and are arranged in a ball-like cluster.
Sputum (Papanicolaou x OI).
Fig. 13.21 Reserve cell hyperplasia in bronchial epithelium. Pulmonary
resection (H&E x MP).
a .. «
V * *
e V >
y f j 1
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:V % ,V
Fig. 13.23 Squamous metaplasia in bronchial epithelium. Pulmonary
resection (H&E x MP).
an epithelial surface that has been damaged by varying environ-
mental living and nonliving toxic agents,79,95-98 the attempted
repair in itself inflicts additional damage on the lung, replacing
the highly functional and protective ciliated bronchial epithe-
lium with a nonfunctional and nonprotective squamous-like
epithelium. Cigarette smoke appears to be the most common
environmental toxin associated with the development of squa-
mous metaplasia.99-104 Chronic bronchitis and bronchiectasis
frequently show foci of this epithelial change.
The development of squamous metaplasia is antedated by a
proliferation of reserve or basal cells. As this proliferation con-
tinues, it begins to form a multilayered epithelium that inter-
venes between the columnar epithelial cells and the basement
membrane (Figs. 13.21 and 13.22). As these reserve cells gradu-
ally mature, an epithelium is produced, progressively resem-
bling a stratified squamous epithelium (Fig. 13.23).
In cytologic materials, reserve cell hyperplasia is recognized by
the presence of tissue fragments composed of small, uniform,
tightly cohesive cells possessing darkly stained nuclei and a thin
rim of cyanophilic cytoplasm. Nuclear molding is present, but
uniformity is also present throughout the fragment. No ten-
dency toward fragmentation of the cluster is seen (Fig. 13.24).
Necrosis does not occur. Reserve cell hyperplasia may at times
be very alarming in appearance and must be distinguished from
small-cell undifferentiated carcinoma. Other small-cell neo-
plasms, such as leukemias and lymphomas, should be confused
with reserve cell hyperplasia, because they characteristically
exfoliate into the respiratory material as single cells. Reserve cell
hyperplasia may be present in all types of respiratory specimens
but is most frequent in bronchial brushings.
Cells from squamous metaplasia may occur as single cells or
as small tissue fragments (Figs. 13.25 and 13.26). As fragments,
they are grouped in a uniform, monolayered cobblestone-like
arrangement with striking uniformity between the cells. Some
fragments may exhibit flattening of one surface, presumably
that which was adjacent to the lumen of the bronchus. Although
they resemble maturing squamous cells, they are smaller and
possess a higher nucleocytoplasmic ratio. As squamous meta-
plasia mimics maturing squamous epithelium, metaplastic cells
of various degrees of maturity may be present. The nuclei may