Page 412 - The Veterinary Laboratory and Field Manual 3rd Edition

Pathology/cytology 381

ably trained veterinary professionals. Liver, gut range of diseases and diagnosis will still be based
sections and other tissues (that is, lymph nodes) on a combination of clinical examination, history
may also be collected under general anaesthesia. and gross findings supplemented by histological
Tissues are prepared using similar techniques to findings and the results of other laboratory tests.
those described for necropsy but in some cases Unstained histological sections may also be used
quick cryostat methods are used to process tis- for immune-fluorescence tests and immune-
sues to speed up the process and provide rapid histochemistry using enzyme labelled specific
diagnostic results (for example, in the case of antisera as a diagnostic tool (see also Chapter 6).
exploratory surgery for neoplastic disease). The Consult specialized texts to find specific proto-
latter is rarely performed in veterinary medicine cols, some useful texts are listed at the end of the
but is not uncommon in human medicine. chapter. In most cases it will be necessary to go
on a training course at a specialist centre before
starting to prepare histological sections.
8.4 Cytology

Cytology, or the study of cells, includes the Interpretation
examination of tissue smears and sediment
analysis of urine and other body fluids such as Veterinary professionals will require special-
joint fluid and transudates or exudates from ized training and years of experience before they
body cavities. Transudates occur in association become proficient pathologists. In order to inter-
with, or secondary to, congestive heart fail- pret histological slides the pathologist needs to
ure, liver failure and other causes of osmotic have a good knowledge of the histology of normal
imbalance. Exudates occur in inflammatory pro- tissues so that abnormalities can be recognized.
cesses following infection or damage to tissues. There are a wide range of ‘artefactual’ changes
Biochemical analysis of body fluids is also useful that may be present if (1) slides are not correctly
to assess the nature of the disease process. There prepared, (2) tissues were not adequately fixed
is often a mixture of cell types in abnormal body or (3) tissues were autolysed prior to collection.
fluids and the predominant cell types present, as This is why it is important to make sure that tis-
well as the appearance of the cells (that is, evi- sues selected for histopathological examination
dence of cell death, inclusion bodies or bacteria/ are as fresh as possible and that they are fixed in
fungi) will give an indication of the nature and 10% buffered formalin (other fixatives may be
extent of the disease process. Cytology is a use- used but check with the referral laboratory). In
ful tool for ante-mortem examination of samples most cases there should be some abnormal and
as well for post-mortem samples. some normal tissue submitted in a section 1 ×
1 × 1 cm in proportion to ten times the volume
of fixative. All specimens sent to a referral labo-
8.5 Examination of samples and ratory accompanied by the correct submission
interpretation of results form (see Appendix 2 for an example), which
should contain information about the case, that
In some cases, the histological appearance of cells is, full clinical history, gross necropsy findings
in stained sections will be diagnostic for a spe- and so on. Some examples of clinical conditions,
cific disease or disease process, for example, viral gross necropsy cases, histology and histopa-
or toxic inclusions in specific cells, but in many thology slides are provided in Figures 8.14 to
cases the changes seen may be representative of a 8.26 and additional background information

Vet Lab.indb 381 26/03/2019 10:26