Final Lecture
 Electron microscopy in pathology
 Tumors
 Non-neoplastic conditions
 Applications of transmission electron microscopy
 Specialised ultrastructural techniques
Human tissues or fluids containing human cells are
sampled mainly for diagnostic purposes, i.e. for the
identification of distinct categories of disease that
can be recognized and treated by clinicians. A
microscopically verified diagnosis is often necessary
for optimizing patient management and, in the field
of cancer at least, many purely clinical diagnoses are
re-assigned
investigation.
by
histopathological
microscopical
The light microscopical examination of haematoxylin and
eosin (H&E)-stained sections of tissue embedded in
paraffin wax is the most important technical procedure for
human solid tissue diagnosis. While light microscopy of
H&E sections remains the basis of histological diagnosis,
newer techniques, such as electron microscopy (EM),
immunohistochemistry, and ‘molecular’ techniques can
now
provide
additional
information
understanding of disease and diagnosis.
to
refine
our
Diagnostic electron microscopy has been important since the
late 1960s and early 1970s. The current literature testifies to
the continuing value of EM in both research and the diagnosis
of cases of human disease that are problematical by light
microscopy. Whatever the numbers, EM should be applied
whenever there is an interpretational difficulty in the H&E
section. Further, EM and immunohistochemistry (and all the
other newer techniques) should be seen as complementary
i.e. both immunohistochemistry and EM can give a more
complete picture of a lesion than either technique on its own.
Nearly
all
ultrastructural
transmission
electron
diagnostic
microscopy
work
uses
(TEM),
to
demonstrate specific or characteristic cellular and
matrix
features,
which
may
enhance
our
understanding and diagnosis of disease (Tables 7
and 8).
Tumours:
In tumour diagnosis, successful characterization of a
given tumour depends on finding its distinctive cell
and/or matrix structures. A wide variety of tumours
can be identified on the basis of their distinctive or
specific ultrastructure (Table 7).
Electron microscopy can also assist in suggesting the
primary site of a metastatic. Finally, the value of EM
in simple confirmation of a suspected diagnosis
should not be underestimated. Diagnosing a lesion is
not a black-and-white issue: pathologists hold
diagnoses with a certain level of confidence, and this
can be increased by an ultrastructural input.
Tumours:
A typical examination protocol is carefully to examine
one block (one grid of ultrathin sections) for 1 hour.
However,
tumours
with
decreasing
levels
of
differentiation may need more extensive searching
several hours and multiple blocks, depending on the
pathologist’s perception of the clinical need of the
diagnostic result.
Non-neoplastic disease:
Currently, EM applied to non-neoplastic disease is perhaps
in a more secure position than EM applied to tumours,
since in tumour diagnosis, the primary objective is often
the determination of the tumour’s cellular differentiation,
in non-neoplastic disease there are many applications
where multiple forms of structural change within a single
organelle,
cell
or
tissue
can
be
identified
(cilia,
epithelium, striated muscle cell, peripheral nerve), which
are indicative of different diseases.
Non-neoplastic disease:
EM has long had a value in identifying microorganisms.
Among the most clinically significant in terms of
numerical incidence are viruses. Other microscopic
organisms can have their diagnosis confirmed or details
of their structure revealed by EM: they include bacteria
such as spirochaetes, protozoa such as Cryptosporidium,
microsporidia and Leishmania (in AIDS), and fungi such
as Candida.
In addition to TEM, there are some, although far fewer,
applications in what one might call ‘specialized’
techniques: scanning EM and other techniques (Table
9).
Over the years, therefore, cell and matrix structures,
which are distinctive or specific for a cell or a disease,
have been identified and this accumulated mass of
information forms the basis of diagnostic electron
microscopy in both tumour and non-neoplastic disease
(Tables 7 and 8).
(Table 9) lists techniques which are designated as
‘specialised’ in that they are not as widely used in
diagnostic laboratories as TEM, and which have fewer
truly diagnostic applications. In many instances, the
images from these techniques confirm a fairly secure
diagnosis based primarily on clinical and histopathological
findings, but they often nevertheless add new details,
which can enhance the understanding of disease.
They are clearly of potential value in research, and it
should be remembered that research findings are
sometimes
precursors
of
diagnostic
tests.
These
techniques tend to be found in diagnostic laboratories
that may also have research responsibilities, where
research has led to expertise in the technique, and
personnel trained and experienced in the technique are
on hand to exploit the technique in rare diagnostic
questions when they arise.
Scanning electron microscopy (SEM)
SEM gives three-dimensional information, especially
on surface features, and very often, therefore, the
images are more easily interpretable (Figure 21a)
than those from TEM.
Scanning electron microscopy (SEM)
Diagnostic applications of SEM are limited. They
include the examination of human hair (Fig. 21a) and
the
identification
of
respiratory
particulates,
particularly asbestos fibres, which can also be
studied
by
X-ray
microanalysis
for
identifying
chemical or elemental composition. The findings may
have legal significance in connection with industrial
exposure .
(Figure.21):Special techniques—1. (a) Scanning electron
microscopy. Human hair shaft. The patient was
investigated for pili torti, where the hair shaft is twisted
and fragile, but SEM analysis indicated trichorrhexis
nodosa, with damage presumed to be due to mechanical or
chemical trauma. (b) Immunoelectron microscopy.
Immunoelectron microscopy
Immunoelectron
immunolabelling,
microscopy
(ultrastructural
‘immunoEM’)
provides
simultaneously the morphological data of conventional
TEM and information on biomolecular composition as
in light microscopical immunohistochemistry.
Immunoelectron microscopy
ImmunoEM data, like those from SEM, tend to be
confirmatory, or add to the scientific understanding of
a clinical condition. However, the potential of the
technique to confirm a diagnosis, to remove some
interpretational uncertainty and to enhance the
confidence with which a diagnosis is held, is very
great.