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Fine-Needle Sampling for Cytologic Analysis: Subcutaneous Masses 1113.e1

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Fine-Needle Sampling for Cytologic Analysis: Subcutaneous Masses Available
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fluid associated with a mass that contains
Difficulty level: ♦
stabilize the mass.
solid tissue (may miss diagnostic cells) ○ Use the nondominant hand to isolate and
Synonyms • Having open container of formalin nearby ○ Insert the needle through the skin and
Fine-needle aspiration (FNA), aspirate, needle (can affect staining of the cells and alter into the mass.
biopsy, fine-needle sampling morphology and rendering smear[s] useless) ○ Pull the needle back slightly while remain-
• Skipping microscopic examination due to ing in the mass, and redirect the needle
Overview and Goal the gross appearance of the aspirate (mast slightly pushing forward again (poking
This simple, quick technique allows retrieval of cell tumors can look oily like a lipoma) inside the mass).
cells from a subcutaneous (SQ) mass with the • Failure to immobilize mass lesions that ○ Repeat this motion several times so that
goal of microscopic recognition of a specific are moveable within the subcutis during the mass is fenestrated in the same area.
diagnosis. aspiration ○ After making 5-7 poking motions, remove Procedures and Techniques
• Copious blood contamination can make the needle from the animal, and rapidly
Indications cytologic interpretation difficult to impos- prepare the slides.
Any recognized SQ mass, but especially any sible. A bloody sample should prompt • Slide preparation and smear (see second
new mass or a mass that has undergone recent repeat sampling, but if that sample too Video)
change in size or texture is contaminated with blood, a different ○ Prepare slides ahead of time by laying the
diagnostic technique (e.g., biopsy) may be clean slides out individually, side by side
Contraindications necessary. on a stable, flat surface.
There are no absolute contraindications, but • Using heat fixing to help cells stick to the ○ If using slides with a frosted area for
severe coagulopathy may result in bleeding glass slide. More often than not, this can marking, the frosted side should be up.
from aspirate site. significantly alter cell morphology. Air-drying Slides should be marked with an animal
is recommended (see procedure, below). identifier and the aspirate location. The
Equipment, Anesthesia • Failure to smear the sample on the glass latter step is particularly important if
Should not require anesthesia or sedation unless slide and allowing the cells to dry in thick, more than one site on a patient is being
the patient is extremely fractious or fearful crowded clumps. sampled.
• Sterile hypodermic needle (1 inch, 20 to 22 • Failure to label the glass slides with appropri- ○ Attach the air-filled syringe to the sampling
gauge) ate patient identifier and location of the site needle.
• Microscope slides (free of dust) sampled ○ Hold the syringe and needle just above
• Pencil or marker (for slide identification) • If sending to a reference laboratory, failure to the first slide, with the bevel facing down
• Syringe (5 to 12 mL) place the glass slides in appropriate protective near the frosted end of the slide at an
• EDTA tube (purple top) and/or red-top tube packaging approximately 45° angle, pointing away
if mass is fluid filled Complications are rare; mast cell tumors may from the frosting.
• Appropriate Romanowsky-type stain (e.g., degranulate after aspiration, causing local swell- ○ Push the syringe plunger to expel material
Diff-Quik) if immediate staining desired ing and bleeding. Failure to properly restrain from the needle onto the slide. Note that
• Microscope, optimally with ×4, ×10, ×20, the patient during the procedure can increase caution should be used if the syringe does
and a higher objective (×50 or ×100 oil risk of injury to the patient and/or handlers not have a Luer-Lok attachment point for
objective) and reduce or preclude sample yield. the needle and there is abundant material
• Optional: unstained slides may be submit- in the lumen of the needle. Although
ted to an outside laboratory for review by Procedure uncommon, such situations can lead to
a clinical pathologist. • There are two ways to perform the technique: sudden ejection of the needle from the
• Optional: fluid may be submitted for cell with or without syringe aspiration. For most syringe when a large amount of pressure
count, microbial culture, or biochemical SQ masses, needle sampling without aspira- is suddenly applied.
analysis. tion is preferred initially. If the mass is fluid ○ One sampling will often provide enough
filled or there is no cellular return by needle material for several slides, although depend-
Anticipated Time sampling alone, syringe aspiration may be ing on the yield, multiple attempts may
<5 minutes to obtain aspirate with additional useful. be indicated. The syringe can be detached,
time to stain and review slides • Generally, there is no need to clip or disinfect refilled with air, and reattached to expel
the area of planned FNA, but it should be additional material on the next slide.
Preparation: Important Checkpoints free of gross debris. ○ Using a clean slide (smearing slide), lay
• Gather supplies ahead of time. • Needle, syringe, and slides should be prepared it perpendicularly over the tissue just
ahead of time so that the collected cells can deposited on another slide. For lymph
Possible Complications and be processed rapidly on sample retrieval. In nodes and most other tissues, no pressure
Common Errors to Avoid some instances, a second set of hands for slide other than the weight of the smearing slide
Common errors (or reasons for suboptimal preparation can be beneficial, particularly if need be added. For thick materials, a small
yield) include multiple aspirations are attempted. amount of downward pressure is applied
• Excessive vacuum pressure during needle • Needle sampling (see first Video) as the smearing slide is moved along the
aspiration (cells may lyse) ○ Prefill the syringe with 3-6 mL of air, but entire length of the sample slide. The goal
• Excessive compression when spreading cells do not attach to the needle. The syringe is to create a thin, even smear of intact
on slide (cells may lyse) will not be used until slide preparation. cells on the sampling slide.
• Inadequate compression when spreading cells ○ Have an assistant restrain the patient so ○ The smearing technique is repeated on
on slide (clumped cells cannot be evaluated) that the mass is readily accessible. all slides containing sample; the same
• Sampling nondiagnostic areas, such as areas ○ Uncap the needle, and hold by the hub smearing slide can be used to prepare
adjacent to the mass or areas of necrosis or in the dominant hand. each slide from the same aspirate unless

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