Chapter 6. Methods of Tumor Diagnosis
Fine-Needle Aspiration and Biopsy Techniques
Carolyn J. Henry and Eric R. Pope
Accurate determination of tumor type and, in many cases, tumor grade is important for determining the most appropriate treatment regimen for companion animal cancer patients. 1 Fine-needle aspiration (FNA), needle core biopsy (NCB), punch biopsy, and open (surgical) biopsy can provide that information for soft tissue tumors. Open biopsy is considered the gold standard for most solid tumors but is invasive and in most instances requires either heavy sedation and local anesthesia or general anesthesia. FNA can usually be performed without any anesthesia in cooperative patients. NCB may require local anesthesia, with or without sedation.
FNA and NCB of easily palpable tumors can usually be accomplished by immobilizing the mass with the nondominant hand and directly guiding the biopsy instrument into the mass. The ability to obtain representative samples with FNA or NCB of deeper masses or those located within body cavities is increased when imaging guidance techniques such as ultrasonography or computed tomography are used. 2,3
Bone biopsy samples are usually collected using a Jamshidi needle or Michelle trephine instrument, although FNA may be possible with lytic lesions. This section outlines the techniques commonly used to obtain diagnostic samples from tumor tissue.
FINE-NEEDLE ASPIRATION (FNA)
FNA is an excellent technique for collecting samples for cytologic evaluation of cytoplasmic and nuclear detail. 4 Since only single cells or small sheets of cells are obtained, details concerning tumor architecture cannot usually be assessed. Examination of FNA samples is useful for differentiating neoplastic from inflammatory lesions. A tumor diagnosis can be made if the cells exfoliate well and have characteristic morphology. Cellular morphology may also allow neoplastic lesions to be classified as benign or malignant.
Materials
• 22- to 25-gauge hypodermic needles (25-gauge needles are used with vascular appearing lesions, whereas 22-gauge needles facilitate collection of more cellular samples in solid tumors)
• 5- or 10-ml syringe
• Microscope slides
Technique
• Scrub the skin over the lesion with antiseptic solution or alcohol.
• Immobilize mass between fingers with nondominant hand.
• Zajdela technique (without aspiration) 5
• Pass the needle percutaneously into the mass.
• Move the needle back and forth rapidly within the mass multiple (5–20) times and redirect the needle into different areas of the mass every few strokes. Sampling should be halted if blood appears in the needle hub, since further sampling will only result in blood contamination that may dilute the sample and obscure the cytologic diagnosis.
• Withdraw the needle from the mass.
• Attach the needle to an air-filled syringe and expel the specimen onto a microscope slide, ensuring that the beveled edge is oriented toward the slide.
• The procedure can be repeated multiple times until an adequate specimen is obtained.
• Aspiration technique
• Attach the needle to a 5- to 10-ml syringe.
• Pass the needle percutaneously into the mass.
• Apply suction by pulling back on the plunger multiple times in rapid succession.
• The needle may be redirected within the mass and the above procedure repeated before withdrawing the needle from the mass.
• Release the plunger before withdrawing the needle from the mass.
• Remove the syringe from the needle and fill it with air.
• Expel the sample onto a microscope slide.
• Slide preparation
• Expel the sample onto the microscope slide near the frosted end.
• Use a second slide to spread the sample into a monolayer before staining. Simply allowing the weight of the second slide to spread the sample is generally sufficient. Applying additional pressure when dispersing the sample on the slide will only result in disruption of the cell membranes and make interpretation of the cells difficult.
Interpretation
• Should be interpreted by a trained cytopathologist ( Chapter 7 )
• Sensitivity, specificity, and accuracy of cytology are similar to histology when performed by a trained cytopathologist.
• The diagnostic accuracy of FNA of deep thoracic and abdominal masses in dogs and cats is reported to be between 70% and 90%. 3
• In a study of FNA samples from malignant tumors, the cellular line of origin was correctly determined in 72% and 87% of dog and cat tumors, respectively. 6
• The sampling and processing technique can have a significant effect on diagnostic accuracy. 7
NEEDLE CORE BIOPSY (NCB)
NCB instruments can be used to collect intact tissue samples from soft tissue tumors. The accuracy of diagnosis is enhanced when larger-gauge biopsy needles are used and when multiple samples are collected from different areas of the mass. 1,8
Materials
• NCB needles
• 14- to 16-gauge recommended
• Manual, spring-loaded, automated models
• Hypodermic needles to facilitate removal of specimen from biopsy needle
• Microscope slides for touch preps (impression smears)
• Specimen cassettes
• Fixative solution(s)
• Suture material, skin staples, or tissue adhesive
Technique ( Figure 6-1 )
• Sedation and local anesthesia (general anesthesia may be necessary for deep lesions or uncooperative patients)
• Clip hair and routinely prep skin.
• A small skin incision can be made when deeper lesions are present.
• Read and carefully follow manufacturer’s directions for use of the biopsy needle.
• Collecting multiple samples with the needle directed in different planes is recommended with larger masses.
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