Page 183 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

162 PART II Diagnostic Procedures for the Cancer Patient

to identify the SLN. In this technique, the contrast medium is training are required for this technique to be fully utilized.
injected in four quadrants around or within the tumor. The first One study in veterinary medicine revealed an accurate and
specific diagnosis rate of 83%.
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contrasting node(s) is identified via imaging providing a surgical
VetBooks.ir target (as opposed to extensive dissection within the lymphatic 8. If evaluation of margins of excision is desired, it is best if the
surgeon indicates the surgical margin on the specimen using
basin to find a lymph node with vital dye). A vital dye, such as
methylene blue, is injected intraoperatively in the same locations tissue ink. Several commercial inking systems are available for
as the contrast agent. The use of the vital dye provides the sur- this use. The resected tissue should be blotted with a paper
geon with visual confirmation of the SLN. Some authors have towel, as the dyes will adhere better to the tissue when the tis-
advocated using lipid-based contrast medium because it slows sue is slightly tacky. The tissue ink is “painted” on the surgical
clearance and therefore may permit imaging for longer periods margins using a cotton swab. The dye should then be allowed
compared with water-soluble contrast agents. In a recent study, to dry for up to 20 minutes before the tissue is placed in
this method was successful at identifying the sentinel lymph formalin. Tissue already fixed in formalin can be marked, but
node in 96.6% of veterinary patients with solid tumors of various the dyes may not adhere as well and drying time is extended.
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histologies. When the pathologist reads the slides and sees tumor cells
at the inked edge, you can be certain tumor cells have been
left in the patient. Different colored ink can also be used to
General Guidelines for Tissue Procurement denote different sites on the tumor, such as proximal margin
and Fixation or deep margin. Even with inking, proper fixation, and pro-
cessing, the clinician must realize the entire margin will not
1. When properly performed, a pretreatment biopsy will not be examined by the pathologist. Rather, representative sec-
negatively influence survival. The metastatic cascade involves tions will be obtained from the inked margin. Therefore any
a series of complex events that are not dependent on the num- guidance that the clinician can give to the pathologist as to
ber of neoplastic cells in circulation (see Chapter 2). On the the most important sections to assess for tumor cells will help
other hand, neoplastic cells contaminate the local tissues sur- the pathologist pay particular attention to such areas. It is
rounding the mass and, in some cases, successfully attach and essential that both the pathologist and the clinician commu-
grow within these normal tissues. Careful hemostasis, obliter- nicate if the pathology report is confusing or does not match
ation of dead space, and avoidance of seromas or hematomas the clinical picture. Of course, margin evaluation is necessary
will minimize local contamination of the incisional biopsy only for excisional biopsy or after curative-intent surgery and
site. Definitive surgery to remove the tumor along with the does not apply to needle-core or incisional biopsies, which by
associated biopsy tract should take place as soon as possible definition will have inadequate margins.
after the biopsy procedure. Surgical drains should not be 9. Stainless steel vascular clips or staples in the resected speci-
placed in biopsy sites, if possible, because the drain tract can men will damage the microtomes used by the pathology labo-
become contaminated with tumor cells and seed tumor cells ratory. Remove them before the tissue is submitted.
through uninvolved tissue planes. In particular, care should 10. Proper fixation is essential. Tissue is generally fixed in 10%
be taken during biopsy not to “spill” cancer cells within the buffered neutral formalin with 1 part tissue to 10 parts fixa-
thoracic or abdominal cavities, where they may seed pleural tive. If more than one lesion has been biopsied, they should
or peritoneal surfaces. each be placed in a separate well identified container. Cer-
2. When biopsies are performed on the limbs or the tail, the tain tissues such as eye, nerve, and muscle may require special
incision should be made along the long axis of the limb or tail fixation techniques. The clinician may want to call and con-
rather than transversely. Transverse incisions are much more sult with the pathologist on how to submit tissue for special
difficult to resect completely. If a biopsy is near the midline, circumstances.
the incision should be oriented parallel to the midline. 11. Tissue should not be thicker than 1 cm or it will not fix prop-
3. Avoid taking the junction of normal and abnormal tissue for erly. Masses greater than 1 cm in diameter can be sliced like a
pretreatment biopsy. Care should be taken not to incise nor- loaf of bread, leaving the deep inked margin intact, to allow
mal tissue that cannot be resected or would be used in recon- fixation. Extremely large masses can be incompletely sliced
structing the surgical defect. Avoid biopsies that contain only as described earlier, fixed in a large bucket of formalin for 2
ulcerated or inflamed tissues. to 3 days, and then shipped in a container with 1 part tissue
4. The larger the sample, the more likely it is to be diagnostic. to 1 part formalin. A less ideal but alternative approach is to
Tumors are not homogeneous and usually contain areas of have the surgeon take representative smaller samples from the
necrosis, inflammation, and reactive tissue. Several samples mass (e.g., soft and hard pieces, red and pale pieces, deep and
from one mass are more likely to yield an accurate diagnosis superficial pieces, etc.) and the lateral and deep margins in
than a single sample. the hope that they are representative. The rest of the mass can
5. Biopsies should not be obtained with electrocautery or laser, be saved in the clinic in formalin in case more tissue needs to
as it can deform (autolysis or polarization) the cellular archi- be evaluated. This extra tissue should never be frozen. Freez-
tecture of the tissue sample. Electrocautery is better utilized ing causes severe artifact in the tissue.
for hemostasis after blade removal of a diagnostic specimen. 12. A detailed history should accompany all biopsy requests.
6. Care should be taken not to unduly deform the specimen Interpretation of surgical biopsies is a combination of art and
with forceps, suction, or other handling methods before science. Without all of the essential diagnostic information
fixation. (e.g., signalment, history of recurrences, invasion into bone,
7. Intraoperative diagnosis of disease by frozen sections, rate of growth, etc.), the pathologist will be significantly com-
although not routinely available in veterinary medicine, promised in his or her ability to deliver accurate and clinically
is used widely in human hospitals. Special equipment and useful information.