Mastering Fine-Needle Aspiration in Veterinary Medicine: Best Practices for Optimal Results

Fine-needle aspiration (FNA) is a widely used technique for sampling lymph nodes in veterinary patients due to its effectiveness in diagnosing and staging neoplastic conditions. It involves using a thin needle to collect cells from lymph nodes, which are then analyzed for diagnostic purposes. The quality of the sample obtained is crucial for accurate diagnosis. Diagnostic samples typically have high cellularity, intact cells, and minimal blood contamination, whereas non-diagnostic samples often suffer from poor cellularity, significant cell lysing, or excessive haemodilution, making accurate diagnosis challenging.

However, some neoplastic conditions, such as fibrosarcoma, certain types of mammary tumors, and low-grade lymphoma, do not exfoliate well during FNA. These tumors are often composed of cells that are either too cohesive or embedded in a dense stroma, making it difficult to obtain a representative sample. In these cases, alternative diagnostic techniques like biopsy may be required to achieve a definitive diagnosis.

Highly cellular liver aspirate

Fine-needle aspiration (FNA) is less effective for certain tumors that do not exfoliate well, meaning they don't release cells easily into the needle. These include:

1. Fibrosarcomas: Dense fibrous tissue makes it difficult to obtain cells.

2. Soft tissue sarcomas: Similar to fibrosarcomas, the dense matrix is challenging to aspirate.

3. Mammary tumors (certain types): Particularly those with a dense or fibrotic stroma.

4. Benign epithelial tumors: Often cohesive and do not shed cells easily.

5. Thyroid carcinomas: May not yield sufficient cells due to their dense structure.

6. Low-grade lymphomas: These often produce scant cellular samples.

These tumors may require alternative diagnostic methods like biopsy for definitive diagnosis.

To achieve optimal results with FNA, the ideal methodology involves using a 22-gauge needle with ultrasound guidance and a 5 mL syringe prefilled with 1 mL of air. During sampling, 3 mL of negative pressure should be applied by withdrawing the syringe plunger, which helps collect cells effectively without causing excessive blood contamination. This careful balance between pressure and technique ensures that the sample is of high diagnostic quality.

This method is supported by data from a study comparing FNA and fine-needle non-aspiration cytology (FNNAC). The study demonstrated that FNA yields higher diagnostic success, with 73.1% of FNA samples being diagnostic compared to 59.6% for FNNAC. FNA samples also showed better cellularity, making them more suitable for accurate cytological evaluation. These findings confirm that using the recommended FNA methodology is essential for obtaining high-quality diagnostic samples in veterinary patients.

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Bibliography:

1. Whitlock, J., Taeymans, O., & Monti, P. (2021). A comparison of cytological quality between fine-needle aspiration and non-aspiration techniques for obtaining ultrasound-guided samples from canine and feline lymph nodes. Veterinary Record, 1-6. https://doi.org/10.1002/vetr.25.

2. Adams, V. J., Evans, K. M., Sampson, J., & Wood, J. L. N. (2010). Methods and mortality results of a health survey of purebred dogs in the UK. Journal of Small Animal Practice, 51, 512-524.

3. Amores-Fuster, I., Cripps, P., Graham, P., Marrington, A. M., & Blackwood, L. (2015). The diagnostic utility of lymph node cytology samples in dogs and cats. Journal of Small Animal Practice, 56(2), 125-129.

4. Withrow, S. J., Vail, D. M., & Page, R. L. (2013). Withrow and MacEwen's Small Animal Clinical Oncology (5th ed.). Elsevier.

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