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Aspirates versus Biopsies - Is There A Difference?

The short answer is: Yes!

Aspirates and biopsies differ on many levels including how the samples are collected, the type of sample that results, and the benefits and limitations of each.

Aspirates, also called fine needle aspirates (FNAs), are cell samples that are collected with a small gauge needle. Aspirates can be taken based on feel, they can be taken based on visualization with the naked eye, they can be taken using ultrasound guidance, and they can be taken endoscopically. In some cases, aspirates can be taken based on guidance from advanced imaging such as CT scans and MRIs. Aspirates can be collected with or without sedation due to the small size of the needle used. Samples collected in this manner generally are fluid samples that contain cells. Although this type of collection is relatively non-invasive, akin to a feel of a vaccination, the tissue architecture is lost with this method. The cell or fluid sample is expelled on to a clean microscope slide and is gently smeared so that the cells are spread out evenly on the slide. The slide is then dried and is often fixed, decolorized, and stained to help keep the cells on the slide and to highlight the various features of the cells present. Because the architecture is lost, it can be impossible to determine the extent or invasiveness of the cells of interest and it can be difficult, in some cases, to know how to properly categorize the cells of interest without this information. Due to the small size of the needle used, it can be easy to miss the area of interest or not collect a representative sample, and instead be collecting the adjacent inflammation, fat, or necrotic/dead tissue. The prepared slide is the submitted for cytology / cytological evaluation by a board certified veterinary pathologist. Cytology generally has a fast turn around time since the samples are small and few.

When it comes to biopsies, biopsies can be collected via:

1. Needle biopsy (larger than one used for a fine needle aspirate) or tru-cut biopsy - this can be during direct visualization, with ultrasound guidance, or with the guidance of some type of advanced imaging modality

2. Punch biopsy (think similar to a hole-punch)

3. Incisional biopsy (cutting a small piece out of an area of interest)

4. Excisional biopsy (removing the whole area of interest for the sample)

5. Wedge biopsy (taking a wedge shaped piece of tissue)

6. Endoscopic biopsy (collected during endoscopy typically with biopsy forceps)

7. Laparoscopic biopsy (collected during a laparoscopic procedure generally with biopsy forceps)

8. etc.

Some sort of visualization is necessary for taking a biopsy so that vital structures including nerves, blood vessels, and normal tissue can be avoided or disruption can be minimized. Visualization is also important for the area to be sutured closed or for pressure or gel foam to be applied to stop bleeding and/or facilitate healing. Biopsy collection almost always requires sedation, anesthesia, or local anesthesia since a piece of tissue is being collected. Exclusions can occur if a piece of tissue is expelled by the patient naturally (ie. during sneezing, coughing, urinating, defecating, etc.) and is collected afterwards. You would be surprised how often this happens. Since a piece of tissue is collected, tissue architecture is maintained which allows for the extent, invasiveness, grade of disease to be determined. It is still possible to miss the area of interest and to collect tissue adjacent to the area of interest, however, this is less likely given the fact that the sample size is larger than one obtained via aspiration. The tissue collected must be hardened in some way to allow the sample to be thinly sliced and processed/stained for histopathological evaluation / histopathology and visualization under a microscope. Samples can be flash frozen which generally is only used so that a surgeon can know in real time if the entire area of interest has been removed, or the samples can be fixed in formalin to allow for full evaluation and analysis of the area of interest. The bigger and more mineralized the tissue, the longer this process takes, so biopsy results / histopathology results generally take much longer than cytology results depending on the tissue type, tissue size, and laboratory. It was interesting for me to learn in school that for large samples, the entire structure is not sectioned, processed, and evaluated. For large samples, only representative samples are sectioned, processed, and evaluated at the laboratory, so it is still possible that the area of interest could still be missed. Fortunately, if there is more tissue left which is often the case, additional sections can be requested for evaluation.

Generally speaking, the cost of cytology is less than the cost of histopathology.

In both cases, only licensed veterinarians can perform biopsies and aspirates regardless of how and where the samples are collected. East Bay SonoVet is happy to collect ultrasound guided fine needle aspirates if indicated and safe to do so during our ultrasound examinations!

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