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Fine Needle Biopsy – a breakdown

Tips for Performing the best Ultrasound guided Fine Needle Biopsy 

By Dr. Pia Hayat and Dr. Veronica Damian

Fine needle biopsies (FNB) provide a relatively quick and painless method of obtaining important information without the need for open surgery.

With good technique and sample recovery, the cells obtained can help to differentiate the origin of the tissue, likelihood of inflammatory process versus neoplasia and can be invaluable in providing prognosis for the patient.

Ultrasound-guided fine needle aspirates can be highly accurate when performed well.


Equipment required

Figure 1: Equipment required for FNB (excluding alcohol swab)

Ultrasound machine with microconvex probe

Microscope slides

25g 1 ¼  inch needles

5ml syringe

+/- 1ml syringe for aspiration

Alcohol swab





  • Obtain image of organ or tissue that requires sampling and zoom in so that the image occupies the whole screen.
  • Check with colour doppler whether there are any major blood vessels within the area to be sampled and try and avoid these if possible. Once you have found your desired aspirate site, wipe area with alcohol swab.

    Figure 1: Equipment required for FNB (excluding alcohol swab)

  • Position the probe at 90 degrees to the skin if possible with a 25g 1 and ¼ inch needle positioned at 30-45 degrees angle with the bevel facing towards the probe to maximise
  • Introduce the needle slowly watching the image on the screen and make several short sharp “wood pecking” motions to increase collection of cells.
  • If the organ or tissue is very fibrous, and cell recovery is poor using the above technique, consider using a 1ml syringe attached to the needle and aspirating (Fine needle aspirate or FNB) whilst performing the “wood pecking” action.
  • Have your assistant monitor the needle hub closely and if there is any evidence of blood, remove needle immediately.
  • Firm digital pressure over the FNB site is performed by your assistant whilst the sample is being transferred to the microscope slides.

    Figure 3. Procedure of expelling sample on to slide

  • Draw air into 5ml syringe then attach to end of needle used for FNB.
  • Quickly expel air from syringe and needle over microscope slide causing tissue sample to be  transferred.
  • Use a second microscope slide to gently spread sample evenly.
  • Rescan the area of the FNB with the ultrasound to ensure no obvious bleeding or haemorrhage (looking for anechoic fluid within the area that was not present prior to the FNB).
  • Repeat process as required to obtain at least 2-3 good quality samples per tissue or organ.


Tips for obtaining the best samples

  • Ensure that the angle of probe and needle are aligned to ensure visualisation of the needle tip in your screen . Sometimes the angle of the needle needs to be more parallel to the skin to reach tissue that is more caudal in the image.
  • The “wood pecking” action of the needle without aspiration is a great technique to obtain adequate cells without blood contamination, but consider aspiration with a 1ml syringe if cell recovery is poor.
  • Consider using a larger needle size – e.g. 23g 1 and ¼ inch if the organ or tissue being aspirated is very firm or fibrous.
  • Gentle but firm spreading of the sample with the 2nd microscope slide is essential – too rough a hand will result in cell damage and rupture and a poor sample for the pathologist to analyse.
  • Air dry your slides as quick as possible for better preservation of the cells.

Until next tip.

Soundiagnosis team.


Read More

Can you differentiate Pleural Effusion cardiogenic from non cardiogenic origin in cats?

The answer is: Yes!  I was listening to a Podcast from the RVC where Dr. David Connolly (cardiologist) mentioned  a study published by Humm,K et al., in the Journal of  Small Animal Pract.(2013 Dec;54(12):656-61). In this study they tested blood and effusion from cats with pleural effusion, to measure NT-ProBNP concentrations and compared the groups of cardiogenic vs non cardiogenic origin.

They found that the NT-proBNP concentrations in the plasma and the pleural effusion were higher in the cardiac group. Thus concluding that measuring the NT-proBNP in pleural fluid can help distinguish cardiac from non-cardiac causes of pleural effusion in cats.

In a clinic scenario, if you have a cat that is in respiratory distress a TFAST ultrasound can detect pleural effusion. We would suggest you drain the pleural effusion immediately under an opioid sedation and run a proBNP. Then, when the patient is stable enough, carry out your further imaging including Thoracic radiographs and Echocardiogram.

How cool is that!
Until the next tip,
Veronica and the Soundiagnosis team


Click here to read the journal article on this study!

Read More