Page 148 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 7 Diagnostic Cytopathology in Clinical Oncology 127

can be identified with imaging, which can facilitate needle place- bounced off the bladder wall in the region of the lesion (typically
ment for aspiration of bone lesions. Cavity effusions are collected using ultrasonographic guidance), taking care not to perforate the
bladder wall. Saline can be flushed into the bladder to facilitate
easily without imaging if fluid volume is significant; however,
VetBooks.ir imaging can target smaller accumulations of fluid and provide a collection of cells and cellular particles, some of which may be
large enough to process for histologic evaluation.
measure of safety. If there is particular concern for hemorrhage
after aspiration, imaging can be repeated to look for evidence of Imprinting and scraping are excellent means of preparing
bleeding at the aspiration site. Collection of cytologic specimens cytologic specimens from tissues obtained by surgical biopsy.
from the eye, brain, and lung requires special consideration and When making imprints, a fresh surface should be exposed on
expertise. the piece of tissue using a scalpel blade and then gently blotted
on absorbent paper until little blood or tissue fluid appears on
Collection Techniques the paper. The tissue is held with forceps, and the fresh surface
is gently pressed repeatedly onto the glass slide, using slightly
Fine-needle aspiration (FNA) is by far the most common method different pressure with each imprint. The final specimen will
for collecting cytologic specimens. Small-gauge needles (22–25 contain a row of imprints of varying thickness, one or more of
g) are sufficient for smaller lesions and result in less hemorrhage. which should be suitable for evaluation. Common mistakes when
Large-gauge needles (18–20 g) may be required to collect suffi- preparing imprints include insufficient blotting and application
cient material from masses containing abundant matrix (i.e., firm of too much pressure, resulting in excessive blood or cellular
masses and sarcomas), but specimens may contain more blood. disruption, respectively. Sometimes mucosal or connective tis-
Medium-sized syringes (12–15 cc) yield more vacuum for aspira- sue is obtained instead of tumor cells if the incorrect surface is
tion than smaller syringes (3–6 cc). The intent of aspiration is to imprinted onto the slide. When tumors such as sarcomas contain
draw cells into the needle shaft, not to fill the syringe with mate- abundant matrix, imprinting will often not yield sufficient num-
rial unless the lesion is fluid-filled. After the needle is inserted into bers of cells for evaluation. The surface of these lesions should be
the lesion, vacuum is maintained in the syringe while the needle is cross-hatched with a scalpel blade and imprinted without blot-
redirected into the tissue several times to collect a broad represen- ting; this may liberate cells embedded in matrix. Alternatively,
tation of cells. This is especially important when aspirating LNs to the surface of firm lesions can be scraped several times in one
evaluate for metastasis. After aspiration, vacuum is released before direction with a scalpel blade held at 45 degrees to the tissue.
removing the needle from the tissue, the needle is removed from The material on the edge of the blade is then gently spread on a
the tissue and then from the syringe, the syringe is filled with air glass slide. When using samples obtained by surgical biopsy to
and reattached to the needle, and the cells are expelled onto a glass prepare cytologic specimens, care must be taken not to disrupt
slide. An alternative technique, often referred to as “fenestration,” surfaces or margins important for histologic evaluation, especially
is to obtain cells without aspiration by holding the needle by the for excisional biopsies in which assessment of tumor margins is
hub between the thumb and middle finger while covering the hub fundamental to the evaluation.
opening with the forefinger (to prevent blood or other fluids from Tissue particles or mucus collected by saline washes or by trau-
escaping) and rapidly and repeatedly inserting the needle into the matic catheterization can be retrieved with a pipette and gently
2
lesion with redirection until cells are packed into the needle shaft. pressed between two glass slides. If washes or cavity fluids are cell-
This method often yields as much cellular material as the aspi- poor, cells in the fluid must be concentrated to prepare slides of
ration technique and produces less hemorrhage and patient dis- sufficient cellularity. Collected fluid can be centrifuged, the super-
comfort. Similar to the aspiration technique, a syringe is used to natant decanted, and the cell pellet or sediment resuspended in
expel the material in the needle onto a glass slide. Alternatively, a a small amount of remaining fluid and then spread onto a glass
syringe, preloaded with air, can be attached to the needle used for slide. Similar to preparation of blood smears, the feathered edge
the fenestration technique before needle insertion into the tissue of the fluid should be included on the slide because nucleated cells
of interest, which allows easy expression of fenestrated material will accumulate there and may be best evaluated at the edge. Alter-
onto slides on exit from the tissue. A second clean slide is then natively, when spreading the suspended cell pellet fluid on a glass
placed on top of the sample and the two slides are pulled apart in slide, the spreader slide can be abruptly lifted off the slide, leaving
parallel, taking care not to exert pressure on the sample. The aim a line of fluid—and concentrated cells—on the slide instead of a
is to obtain a monolayer of intact cells. Failure to spread the speci- feathered edge. The best method to concentrate cells in cell-poor
men immediately leads to a sample that is too thick to interpret; fluid samples is to use a cytocentrifuge, but most veterinary prac-
conversely, aggressive pressure on the sample may rupture many if tices lack this equipment.
not all cells, also leading to a nondiagnostic specimen.
Cytologic material may be collected from mucosal surfaces Cytologic Stains
such as the respiratory, gastrointestinal, and genital tracts by
saline washes or with a brush or biopsy forceps inserted through A variety of quick stains are available for immediate examination
an endoscope. Cytologic materials collected using an endoscopic of cytologic specimens and include quick Romanowsky stains,
brush are gently rolled onto a glass slide and often result in highly such as Diff-Quik. A specific set of staining jars should be kept
cellular smears. In contrast, rolling a cotton swab over the surface exclusively for cytologic specimens and not used concurrently for
of a lesion is only moderately successful at collecting sufficient dermatologic specimens. The jars containing the stain compo-
material for cytologic evaluation of tumors. Traumatic catheter- nents should be capped between uses to prevent evaporation and
ization is the preferred method for collecting cytologic material contamination of the fixative and stains. Maintenance, including
from bladder masses because of the potential risk of seeding tumor scheduled replacement of stain components, is important to avoid
cells when transitional cell carcinomas (TCCs) are aspirated trans- artifacts such as stain precipitate and contamination with organ-
3
abdominally. Traumatic catheterization is accomplished with an isms or debris that might be misinterpreted. Slides should be com-
open-ended polypropylene urinary catheter attached to a large pletely air-dried before fixation in the methanol fixative. Stains
syringe (50–60 cc). The catheter is inserted into the urethra and must thoroughly penetrate the smear, and in well-stained smears