QUARTERLY BEAT
JULY 2026
numerous times with 9 different techniques among several clinicians with no means to control intratumoral trauma from multiple aspirations. Finally, absolute cell quantity should not be equated to diagnostic yield, which was not evaluated. In other words, more cells may not be advantageous if a lower number of cells of a highly exfoliative tumor provides a diagnosis. Recall that Launay et al. found no differences in final cytologic diagnosis among needle sizes despite larger needles yielding more cellularity. One final consideration is the impact of needle size on pain. In the study by Launay et al., a 27G needle produced the least adverse reactions in non-sedated patients during splenic aspiration. Although non-sedated techniques are reported, the author strongly recommends sedation or analgesia unless there is a medical reason not to do so, which is quite uncommon, even in debilitated patients. In addition to the obvious patient welfare considerations, sedation anecdotally results in a faster sample acquisition time due to patient compliance. For now, it appears any needle size between 22-25G should yield similar diagnostic quality results with a theoretical: a larger gauge may obtain more cells and damage them less, but a smaller gauge may confer less blood contamination in some but not all organs. At this time, the author uses 22G, 1.0 – 1.5 needles as long as the patient is adequately sedated. Other radiologists (Mattoon 2021) report similar success with 25G needles as their standard and only use a larger gauge if the initial results are non-diagnostic.
In light of the evidence, clinicians should feel empowered to adapt to individual circumstances. For example, at the author’s institution, a FN- NA technique is always used initially to obtain 3 samples from each site. If the initial samples are perceived to be of low cellularity, 2-3 more are obtained using the FNA technique. Anecdotally, follow-up FNA appears to improve diagnostic yield in some lesions that do not initially exfoliate well with FN-NA. If an FNA technique is used, the size of the syringe should be considered. Most operators report improved dexterity when using a small syringe (Liffman 2017). In addition, a small syringe (3-5 mL) may provide adequate suction while minimizing cell trauma and blood contamination. In contrast, a larger syringe will provide more suction but risks damaging or hemodilution of the sample. For small lesions or in locations with vital surrounding structures, attaching the needle and syringe to an extension set allows the operator finer motor control while another individual applies suction with the syringe. The author finds this particularly helpful when obtaining samples from gallbladders, small pockets of effusion, or even small nodules or tissues. If a FN-NA technique is used, multiple passes should be used to increase the odds of a diagnostic yield. Limited evidence and common sense suggest the rate of a definitive diagnosis increases with each needle pass, but likely declines after a certain number. At this time, it appears that 4-5 passes are required to optimize diagnostic yield. Regardless of if the FNA or FN-NA technique is used, each lesion or tissue should be sampled multiple times as cells or diseases can be heterogeneously distributed throughout. Although the optimal number of samples is not well studied, the author’s institution usually obtains a minimum of three, but increases for poorly exfoliative tissues.
TECHNIQUE
Although the phrase “fine needle aspiration” is used in general terms for ultrasound-guided needle sampling, two distinct techniques exist that differ in their use of suction: fine needle aspiration (FNA) and fine needle non-aspiration (FN-NA, also referred to as the pincushion, advance- withdraw, or woodpecker technique). True FNA involves the use of a syringe of varying size, commonly between 1- 20 mL, to generate suction that pulls cells into the needle and hub. In contrast, FN-NA relies on the cutting action of the needle to pack cells inside with 3-5 passes, which are then trapped with capillary tension. The majority of human studies on various abdominal tissues have demonstrated the FN-NA obtain samples of superior quality), especially for the spleen and lymph nodes (LeBlanc 2009, Liffman 2017, and Flemming 2019). However, poorly exfoliative tissues such as the pancreas and kidneys may benefit from an aspiration technique (Liffman 2017). Although veterinary studies are less numerous, one (LeBlanc 2009) looking at splenic aspirates and one looking at hepatic aspirates (Fleming 2019) both found that a FN-NA technique resulted in more diagnostic quality samples with improved cellularity and cell preservation as well as reduced blood contamination. In addition, rotation of the needle during sampling may also increase diagnostic yield (Mattoon 2021). The same findings may not be true for non-abdominal samples of certain tumor types (Blacklock 2018), but for now, FN-NA appears to be superior when sampling abdominal viscera such as the liver and spleen.
. Figure 4. Demonstration of the FN-NA technique. Photo courtesy of Tom Thompson, MSU- CVM photographer.
Finally, while review of slide preparation and staining is beyond the scope of this presentation, techniques include the squash prep, blood smear, line smear,
20 VETGIRL BEAT EMAGAZINE
VETGIRLONTHERUN.COM
Made with FlippingBook - Online Brochure Maker