Fine needle biopsy for cytology

Adapted from: Katie M. Boes, DVM, MS, DACVP
Virginia–Maryland College of Veterinary Medicine

Introduction

Fine-needle aspiration biopsy is used to obtain diseased tissue for microscopic cell examination (i.e., cytology). It can be helpful in the initial or definitive diagnosis of infections, neoplasms, or other clinical conditions. Fine-needle aspiration can be performed with a needle attached to a syringe (fine-needle aspiration) or with a needle alone (fine-needle capillary aspiration). Fine-needle aspiration is preferred for obtaining tissue with normal or poor vascularity, as well as tissue with fibrous stroma. However, fine-needle capillary aspiration can be used to reduce blood contamination when the lesion is suspected to be highly vascularized (e.g., thyroid, hemangiosarcoma) or when aspiration pressure is likely to cause cell rupture (e.g., thyroid cells and some lymphomas).

This guide focuses on fine-needle aspiration biopsy of solid peripheral tissues, such as peripheral lymph nodes and solid skin lesions. Sampling internal tissue may require confirmation of adequate hemostasis (e.g., sufficient platelet count, normal coagulation tests), patient sedation, ultrasound-guided sampling, and longer biopsy needles. Aspiration of fluid-filled lesions requires collecting the fluid in an EDTA-filled tube (purple cap) for optimal cytological evaluation and/or in a tube without anticoagulant (red cap) for culture or chemical analysis. It should be noted that the author recommends using EDTA only for fluid aspirations (e.g., cysts, vitreous samples), and not for samples with a suspected small volume.

cytology Cytology is the study of cells – their structure, function, and changes in disease. In veterinary medicine (as in human medicine), cytology usually refers to the microscopic examination of individual cells taken from tissues, body fluids, or lesions.

Purpose of the cytological examination:

• Diagnosis of diseases, in particular:
  • Neoplasms (e.g. tumors)
  • Inflammations
  • Infections
• Differentiation between benign and malignant processes
• Follow-up examinations, e.g., during therapy monitoring

Advantages of cytology:

• Quickly implementable
• Minimally invasive (e.g. by fine needle aspiration)
• Cost-effective as a tissue biopsy
• Low risk for the patient

The cells are stained and examined under a microscope. A pathologist or trained [person] Veterinarian It then assesses cell shape, cell nuclei, cell distribution and possible pathological changes.

🔍 Most common applications of fine-needle biopsy cytology in small animal medicine

The Fine needle biopsy (FNB) Cytology is a minimally invasive method for obtaining cells for cytological examination. It is frequently used in small animal medicine because it is quick, safe, and usually requires no anesthesia.

🐶 1. Examination of skin and subcutaneous tumors

• Most common area of application the FNB
• Diagnostics of:
  • Lipomas
  • Mast cell tumors
  • Sebaceous cysts
  • Abscesses or granulomas
• Goal: Differentiation between inflammatory, benign or malignant processes

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🐱 2. Assessment of enlarged lymph nodes

• Very common indication in dogs and cats
• Serves to clarify:
  • reactive lymph node enlargement
  • inflammatory changes
  • lymphomas or others metastatic tumors
• FNB is particularly helpful for initial assessment prior to histological examination.

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🐾 3. Cytological assessment of internal organs

• Ultrasound guidance is possible in the following cases:
  • liver
  • spleen
  • kidney
  • thyroid
• In cases of visible changes (e.g., nodules or cysts), FNB provides valuable information for further investigation.

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🧪 4. Puncture of fluid-filled structures

• Liquid contents of cysts, effusions, or abscesses can also be obtained via FNB.
• Examples:
  • cysts (e.g. thyroid cysts, skin cysts)
  • Ejaculations in the abdominal or chest cavity (use EDTA tubes if necessary)

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👩‍⚕️ Conclusion

The Fine needle biopsy is an indispensable tool In veterinary practice, it allows for the rapid and targeted collection of cytological samples – especially in cases of externally palpable changes. It enables an initial diagnosis. diagnostic classification, without the need for an invasive biopsy. In cases of unclear or difficult-to-interpret findings, it is the first step towards further diagnostics.

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Some of the most common errors in sample preparation are:

• Excessive negative pressure during fine-needle aspiration causes cells to lyse.
• Excessive pressure during the production of pressure preparations also leads to cell lysis.
• Insufficient pressure with thicker preparations
• Samples are taken from non-diagnostic areas of the lesion, e.g., necrotic centers or superficial ulcers.

Rapid stains can be used for evaluation of samples with an internal microscope; however, most clinical pathologists prefer evaluation of samples treated with laboratory stains. If the samples are intended for evaluation by a pathologist, at least one slide should remain unstained.

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Step-by-step: Fine needle aspiration

Target: Collect representative cells from the primary lesion. This requires redirecting the needle in the target tissue, avoiding non-diagnostic areas (e.g., necrotic centers of large masses) and areas with secondary inflammation or infection (e.g., superficial ulcers).

Materials needed:

• Gloves
• Gauze or cotton balls soaked in 70 % isopropyl alcohol
• Syringes (6–12 mL)
• Needles (1–1.5 inches; 20–22 gauge)
• Sterile 4 % Disodium-EDTA
• 2–10 clean glass slides
• Firm, flat surface
• Hair dryer (optional)
• Writing utensil (e.g. pencil, microscope slide marker)

Steps:

a) Prepare materials and sampling site. Place 2–10 clean microscope slides on a firm surface. Attach the needle to the syringe, then moisten the needle and syringe base with sterile EDTA solution. Clean the sample area with alcohol.

b) Stabilize the tissue with one hand. With the other hand, insert the needle (at an upward angle), then pull back the plunger and release it. Adjust the negative pressure according to the tissue consistency. Do not apply pressure to any one area for more than a few seconds to avoid blood thinning.

c) Redirect the needle to another area without completely removing it. Withdraw the plunger and release, repeating up to 4 times depending on the lesion size.

d) Remove the needle completely. Tissue is located in the shaft and base of the needle. Remove the needle, pull back the plunger, and fill the syringe with air.

e) Replace the needle. Place the needle tip (slanting downwards) onto the glass slide and position the sample with pressure (approx. 1.25 cm from the matte edge).

f) Prepare pressure slides before the sample begins to dry.

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Step-by-step: Fine-needle capillary sampling

Steps:

a) Prepare materials and sampling site as above. Moisten needle and syringe tip with EDTA, then remove needle from syringe. Clean with alcohol.

b) Stabilize tissue, insert needle (at an angle upwards).

c) Redirect the needle to another area, up to 4 repetitions depending on the lesion size.

d) Remove the needle. Tissue is located in the shaft and base.

d) Fill the syringe with air, replace the needle, and apply the needle tip to the slide and sample.

e) Prepare print preparations (see below).

Author's note:
Correct placement of the sample on the slide ensures that the preparation is centered. Otherwise, it may be lost during staining or application.

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Step-by-step: Pressure preparations (squash technique)

Target: Distribute the cells in a monolayer without lyseing them.

Author's note:
Dust and microscopic glass fragments can lyse cells. Clean slides with a dry cloth before use.

Steps:

a) Allow to air dry or use a hairdryer (cool setting). Label the slide with patient and tissue information.

b) Hold the slide with the sample between your thumb and forefinger. Hold a second clean slide over it.

c) Gently lower the upper slide to distribute the specimen. Apply slight pressure if the material is thick.

d) Carefully pull the slides apart in opposite directions, holding them parallel.

Frequently asked questions about fine needle biopsy for cytology

Summary: Fine-needle aspiration biopsy for cytology in small animal medicine

The Fine needle biopsy for cytology is a key diagnostic tool in modern small animal medicine. It enables the rapid, gentle, and minimally invasive collection of cell material for microscopic examination. It is particularly useful in cases of suspicious lumps, enlarged lymph nodes, or internal organ changes. Fine needle biopsy for cytology important information about the type of change – whether it is a benign process, an inflammation or a malignant neoplasm.

The Fine needle biopsy for cytology It can be performed using two techniques: classic aspiration with a syringe or capillary aspiration without negative pressure. Both methods aim to obtain representative cell material from the lesion. For veterinarians, the Fine needle biopsy for cytology It is particularly useful because in most cases it can be performed without anesthesia or extensive preparation, yet it provides highly relevant information.

A typical area of application of Fine needle biopsy for cytology This method is used to diagnose skin and subcutaneous tumors in dogs and cats. It allows for a rapid differentiation between inflammatory, infectious, or neoplastic causes. It also includes the examination of enlarged lymph nodes. Fine needle biopsy for cytology This is common practice to differentiate reactive processes from malignant lymphomas.

The Fine needle biopsy for cytology It is also helpful for examining internal organs, for example, to investigate changes in the spleen, liver, or thyroid gland – often performed under ultrasound guidance. Fluid-filled lesions such as cysts or effusions can also be effectively visualized using this method. Fine needle biopsy for cytology They can be examined if they are correctly prepared and fixed on suitable microscope slides.

A particular advantage of the Fine needle biopsy for cytology Its low invasiveness is a major advantage. For pet owners, this means a low risk, and for the animal, a stress-free sample collection. Nevertheless, the Fine needle biopsy for cytology exhibiting astonishingly high diagnostic accuracy – provided the technique is applied correctly and the cell material is interpreted correctly.

In daily veterinary practice, the Fine needle biopsy for cytology plays an important role – both in initial diagnoses and in monitoring disease progression. In particular, tumors such as mast cell tumors, lipomas, carcinomas, or fibrosarcomas can often be detected using this method. Fine needle biopsy for cytology This allows for clear classification. Inflammatory diseases such as bacterial abscesses or parasitic skin infections can also be detected early in this way.

It should be noted that the Fine needle biopsy for cytology A definitive diagnosis is not always possible. Particularly in cases of unclear or borderline cytological findings, further histopathological examination is necessary. Nevertheless, the Fine needle biopsy for cytology in many cases as a fast and effective first step in the diagnostic chain.

The use of preventive examinations is also possible. Fine needle biopsy for cytology These methods can be used – for example, to assess newly appearing nodules or chronic skin changes. The information obtained helps to avoid unnecessary surgical interventions or to plan them more effectively.

Furthermore, the Fine needle biopsy for cytology An economically attractive method: It is cost-effective, quick to implement, and can be used in any small animal practice with minimal material requirements. Integration into daily practice is therefore straightforward, which makes it Fine needle biopsy for cytology especially suitable for home visits or emergency situations.

In conclusion, it can be said that the Fine needle biopsy for cytology It represents an indispensable tool in modern veterinary medicine. Its combination of speed, reliability, and diagnostic accuracy makes it one of the most valuable examination methods for both veterinarians and pet owners.

Conclusion: Whether for the initial examination of a lump, for the clarification of internal organs, or as part of oncological diagnostics – the Fine needle biopsy for cytology is a versatile, reliable and essential procedure that has become indispensable in small animal practice.

Sources:

• Meinkoth JH, Cowell RL, Tyler RD, Morton RJ. Sample collection and preparation. In: Cowell RL, Valenciano AC, eds. Cowell and Tyler's Diagnostic Cytology and Hematology of the Dog and Cat. 4th ed. St. Louis, MO: Elsevier Mosby; 2014:1-19.
• Meyer DJ. The acquisition and management of cytology specimens. In: Raskin RE, Meyer DJ, eds. Canine and Feline Cytology: A Color Atlas and Interpretation Guide. 3rd ed. St. Louis, MO: Elsevier; 2016:1-15.