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Ultrasound guided Fine Needle Biopsy (FNB) – a breakdown

Updated: Oct 25, 2023

Tips for Performing the best Ultrasound guided FNB

By Dr. Pia Hayat and Dr. Veronica Damian

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

  • Ultrasound machine with microconvex probe

  • Microscope slides

  • 25g 1 ¼  inch needles

  • 5ml syringe

  • +/- 1ml syringe for aspiration

  • Alcohol swab

Figure 1: Equipment required for FNB

(excluding 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 2: Position of needle and probe prior to FNA

  • 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.

Figure 3: Procedure of expelling sample on to slide

  • Firm digital pressure over the FNB site is performed by your assistant whilst the sample is being transferred to the microscope slides.

  • 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 (Figure 4):

  • 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 the next tip, Soundiagnosis team.

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