Page 2236 - Cote clinical veterinary advisor dogs and cats 4th

1113.e2 Fine-Needle Sampling for Cytologic Analysis: Subcutaneous Masses

it is contaminated with blood or very Postprocedure dissolve lipid, and if the material seems to
thick material. Sometimes, the smearing Little aftercare is required. Rarely, animals with disappear and cytology is acellular, lipoma
VetBooks.ir ○ Slides may be air-dried (recommended) or and they should be watched for 30 minutes or • Whether or not the smears are stained and
is likely.
mast cell tumors may experience complications,
slide itself has a nice sample and can be
processed for cytology.
so after the procedure. Rarely, vascular lesions
interpreted within your clinic, it is worth
dried with a cool blow dryer before stain-
ing. For air-drying, hold the glass slides by hemorrhage after FNA. having a cursory microscopic evaluation
the frosted edge (or for nonfrosted slides, Alternatives and Their
along the end of the slide where no cells Relative Merits
have been placed) between two fingers, • A pet owner may choose to simply “watch”
and gently fan the slides through the air a mass for any change rather than pursue
for a few seconds. Avoid this step if the a specific diagnosis. Delay in diagnosis of
slide contains abundant hemorrhage or malignancy may negatively impact outcome.
material that may dislodge from the slide • Surgical removal of a mass can provide
when fanned. diagnostic information and may be curative.
○ Diff-Quick or similar stain is applied • Excisional biopsy may be indicated if FNA
to at least one slide, or special stains is nondiagnostic, although biopsy and
(e.g., Gram stain for bacteria) may be FNA should be regarded as complementary
used. methods. Whenever possible, both are
○ Reference laboratories generally prefer optimal to collect. A
to receive unstained slides, but at least • Advantages of FNA/cytopathology over
one slide should be checked in house to biopsy are rapidity, availability in house (or
be sure that there are adequate cells for through reference lab), low cost, superior
interpretation. individual cell detail (nuclear chromatin
• Aspirate sampling (see third Video) features, cytoplasmic granules, or small
○ For fluid-filled masses or if needle organisms are more readily visualized on
sampling fails to produce tissue, a dif- microscopy). Disadvantages include inability
ferent collection technique (aspiration) is to assess tissue architecture (e.g., capsular or
preferred. lymphatic invasion) and limited tissue to B
○ For aspiration sampling, an empty pursue additional stains.
5-10 mL syringe is attached to the needle
before sampling. Pull the plunger back Pearls
to break the seal, but then empty the air • Benign lipomas (p. 591) are perhaps the most
from the syringe before sampling. commonly encountered SQ mass. Typically,
○ Instead of using the fenestration motion, these appear grossly as a shiny, clear liquid C
the needle (attached to syringe) is simply (oily) on the slide. It is wrong to make the
inserted into the mass and negative pres- diagnosis of lipoma based only on the gross FINE-NEEDLE SAMPLING FOR CYTOLOGIC
ANALYSIS: SUBCUTANEOUS MASS A, Glass
sure applied by pulling back the syringe appearance of the slide because mast cell slides with frosted edges. B, Green needle (20 gauge),
plunger. tumors can look the same way. The slide blue needle (22 gauge, most commonly used), red
○ For a solid mass, the syringe plunger is should always be prepared by smear and needle (25 gauge). C, A 6-mL syringe with Luer-Lok
pulled back (typically to the 1-3 mL mark) examined microscopically. Typical stains may (arrow).
several times in rapid succession.
○ When no negative pressure remains in
the syringe, the needle is removed from
the animal.
○ The syringe is disconnected from the
needle.
○ The syringe is then filled with air and
reattached to the needle, and sample
preparation proceeds as above.
○ If the mass is fluid filled, the syringe
can simply be filled with fluid during
aspiration.
○ Very minute amounts of fluid can be
placed on several slides that are then A
prepared as described.
○ Remaining fluid can be placed in an
EDTA and/or clot tube. This fluid can
be characterized by culture, concentration
techniques, or other methods. If a fluid
is processed to produce concentrated
aliquots and smears in clinic and the
smears are subsequently forwarded B C
to a reference laboratory, notify the FINE-NEEDLE SAMPLING FOR CYTOLOGIC ANALYSIS: SUBCUTANEOUS MASS A, Unstained
lab and include a nonconcentrated nucleated cells highlighted by red ovals. Pale outlines of nuclei are visible (green arrow highlights one nucleus).
smear (and/or fluid sample in a tube) Many erythrocytes in the background (black arrows highlight a few). B, A small cluster of pale, unstained nucleated
alongside the concentrate smears/tube cells surrounded by hemorrhage. Green arrows highlight nuclei of a few cells. C, A large cluster of unstained
samples. nucleated cells creating a pale thick deposit (left) surrounded by abundant, thick hemorrhage (right and bottom).

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