Diagnostic Cytology
Fig. 8.132 In a liquid-based cytology specimen, all the cell material is
concentrated and evenly distributed within a circular centrically located area
on the glass slide (Papanicolaou x LP).
be carried out without the need to take a repeat smear since
there is residual cell material left in the vial. Finally, the thin
layer of cells may facilitate automated prescreening.
Worldwide, different LBC procedures are in use. The two
most widely used liquid-based systems are the ThinPrep
system (Hologic, Marlborough, MA) and the AutoCytePrep
system (currently known as SurePath; BD-Tripath, Burling-
ton, NC). Both systems were approved for cervical screening
programs by the US Food and Drug Administration (FDA)
(see Chapter 5).
In general, LBC specimens must contain a minimum of
5,000 well-preserved squamous cells (conventional smears:
8,000-12,000) before evaluation can be "satisfactory." Also, like
Fig. 8.133 Normal cervical squamous and columnar cells in a liquid-
based specimen with well-preserved cytoplasmic morphology and distinct
nuclear detail with transparent chromatin structure (Papanicolaou x HP).
conventional smears, LBC specimens must contain cells from
the transformation zone (endocervical or squamous metaplastic
cells), and each cytological report must contain, besides a "sat-
isfactory" statement, an additional quality that the transforma-
tion zone component is present78 (see Chapter 6 ).
The overall quality and the morphological pattern of thin-
layer specimens are somewhat different from that of conventional
smears. The preservation of epithelial cells is well comparable for
both thin-layer techniques. There are no air-drying artifacts and
the cellular material is more concentrated and evenly distributed
within the circular area (Fig. 8.132). The background is clean and
there are more single cells to evaluate because of less obscuration
by inflammatory cells or blood cells. Cell sheets and cells in a syn-
cytium are still present, as in the case for inflammatory cells. The
latter are often attached to epithelial cells or concentrated in small
clusters. Cytomorphologically microorganisms, radiation changes,
repair, ASCUS, and LSIL are comparable to that of conventional
smears. Tumor diathesis is preserved. Atrophy is characterized
by a background of degenerative cellular debris with dispersed
atrophic cells. Normal endometrial cell groups are better preserved
than in conventional smears and present as well-preserved, small
rounded, 3-dimensional groups of which the nuclei show small
chromocentra and chromatin clearing. Because of wet fixation the
cells will round up and may exhibit more nuclear and cytoplasmic
detail (Fig. 8.133). The cells may appear smaller and it is neces-
sary to evaluate hyperchromatic small metaplastic cells carefully
for nuclear atypia and look for normal reference cells to avoid
overdiagnosis. Dysplastic cells frequently lie isolated, in contrast
to the clustering seen in conventional smears. Highly diagnostic
for HSIL cells is the presence of 3-dimensional nuclear structural
abnormalities ("cerebriform" indentations) clearly seen by micro-
focusing the specimen (Fig. 8.134). For additional information
and illustrations see Chapter 5.
Although LBC techniques were only recently introduced,
many studies in which one of these two techniques is com-
pared with the conventional Pap smear are already available.
Most studies use one of two possible study designs. In so-called
"split-sample" studies, one collection device is used for both
techniques. First, a conventional smear is made, after which a
LBC specimen of the material remaining on the sample device
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