gross appearance of specific neoplasms rarely is distinctive. Even
differentiating neoplastic from non-neoplastic lesions, based upon
gross characteristics, is problematic. Examining impression smears
and fine-needle aspirates provides some additional information, but
these samples still lack the full context of cellular arrangements
and relationships to adjacent structures. Histologic evaluation of
solid tissue (biopsy specimens from clinical patients, or specimens
taken at necropsy) is a powerful diagnostic tool.
Sampling strategies are dictated by lesion size, location, cosmetic
outcome, and diagnostic utility. Small (≤1cm diameter) lesions often
can be removed completely, including a normal tissue margin.
Overzealous squeezing, crushing, electrocautery, or laser
application causes disturbing artifacts in these small samples;
handle them gently. Larger lesions may still be removable in toto,
and submission of whole masses allows for thorough interpretation of
not only the lesion features, but also the excisional completeness.
Orienting the specimen to the excision site can be done with simple
verbal descriptions, or variously placed sutures, or use of
multicolored inks applied at specific edges or surfaces. Such
landmarks aid in the proper trimming, sectioning, and evaluation of
the whole lesion by the pathology laboratory personnel. Similar
distinctive markings can allow proper identification of each
specimen, when several lesions are submitted simultaneously in the
same container. If you receive a report from a pathologist saying a
tumor was removed with the clean margins except in one small area,
one of the first things an Oncologist will ask- is what area was
that in the patient? Preparing samples before submission makes the
information you receive more useful.
The location of some large lesions will preclude complete
surgical removal. Clinicians must judge how much tissue can be
taken, to allow reasonably functional healing, while providing
representative samples for diagnostic purposes. Active edges of
lesions typically are more useful than necrotic cores, though the
most informative specimens of damaged bone (e.g., osteosarcoma)
often come from the lesion center.
Nearly all histopathology can begin with tissues fixed in 10%
buffered neutral formalin. Some special fixatives have been touted,
but these require additional attention to sampling, fixation time,
processing quirks, tissue storage, and fixative disposal. Formalin
doesnt penetrate tissues rapidly, and specimens much more than 8mm
thick [the other two dimensions are not particularly relevant] will
not fix in 24 hours. Use care in slicing a large specimen to enhance
fixation; too often, these specimens are nearly shredded, such that
interpretation of the whole mass is impossible. Exceptions are eyes,
brains, and spinal cords, which are better fixed whole. These
tissues are so delicate that slicing them when fresh causes more
interpretive problems than just letting them fix slowly. Fixative
volume should be 10-20 times the tissue volume. After 18-24 hour
formalin immersion, samples can be transferred to a container with
just enough formalin to keep the specimen moist, for shipment to a
pathology laboratory. There is no need to send large volumes of
fixative; it is just more expense, and an opportunity for leakage or
breakage. Occasional specimens, such as an entire amputated limb, or
a whole, enlarged spleen, are difficult to sample thoroughly, or to
fix properly. Those sorts of large, intact specimens can be
refrigerated and shipped fresh (unfixed) in an insulated container.
The pathologist can select and fix representative samples for
histologic evaluation, and retain the rest of the specimen for
additional dissection, if needed. Sending the entire organ or mass
may sound gruesome but it is far preferable over sending a portion
that either leads to no diagnosis or limits what can be said about
margins of the resection.
The specimen(s) should be accompanied by a thorough clinical
history. Descriptions of location, size, shape, color, consistency,
rate of growth, and any effects on the patient should be included
for each sample. Most tissue processing on well-fixed soft tissues
will yield hematoxylin and eosin-stained glass slides by the next
working day, following receipt of the specimen. Samples of bone will
require some additional processing time [usually 1-2 days] to allow
sectioning of such specimens. Histopathologic results are reported
(by telephone, FAX transmission) routinely the same day that the
glass slides are received by the pathologist. Some specialized
techniques (other histochemical stains, or immunohistochemistry, or
molecular diagnostic procedures) are powerful ancillary steps, which
may require another day or two of processing.
A final, written histopathology report will include two
components; a detailed description of the tissue findings, and (more
important for the clinician) an interpretation of the diagnosis and
its implications. Such interpretations of neoplasms should include
tumor grading and staging, when appropriate.
Veterinarians who use a diagnostic facility for histologic
evaluation of neoplasms will become familiar with the particular
laboratorys capabilities. When in doubt, call the laboratory. Not
every laboratory does everything, and not every laboratory does
everything exactly the same way as all other laboratories.
Veterinarians who provide histopathology service are interested and
integral colleagues in the care and management of patients,
especially those with neoplasms.
Written by Dr Charles Leathers, Washington State University.