In this presentation, real-time ultrasound clips are used to illustrate abnormal appearances of abdominal organs. In addition, interventional methods such as fine needle aspirate and ultrasound guided biopsy techniques are reviewed.
Guidelines for ultrasound guided or directed interventional procedures are summarized as follows:
Tissue Sampling Procedures
Tissue sampling methods include fine needle aspirate and biopsy. Both can be done through a ultrasound guide. However, with experience, most operators prefer to perform the procedure as a free-hand technique. This is especially true, when you are doing fine needle aspirate.
Fine needle aspirate
Fine needle aspirates can be done using a variety of needles. There are many commercially available needles. Yet, they are often expensive and limit the use in veterinary practice. Commonly, a 22G or 25G hypodermic needle (1 inch length) is used connected to a 5 or 6 ml syringe. The deeper tissue sampling is more difficult and often requires use of along spinal needle.
In most cases, sedation is not necessary but certainly facilitates good sampling. The area of the aspirate should be cleaned by alcohol. The skin surface should be kept as flat as possible. This is a real key to the success of fine needle aspirate. The needle is inserted in a tissue or organ under real-time ultrasound observation. The operator should pay attention to maintain the plane of ultrasound and insertion plane of the needle in a same plane. As the needle is advanced, the tip should be always visible. If the needle tip is not visible, the plane should be re-examined. It is helpful to look down the transducer and needle to see if the planes match.
There are different aspiration techniques. In a solid tissue, a negative pressure exerted by a syringe is necessary to gain samples. However, some prefer to jam a needle into an area of interest to sample tissues. This method is often rewarding in case of congested organs or blood-rich lesions.
Cytology slides should be made immediately to prevent blood clotting.
Fine needle aspirate does not carry a severe risk. Yet, most veterinarians should check blood clotting parameters prior to the procedure.
Tissue core biopsy
This procedure carries somewhat of a risk. Patient selection should be carefully performed. In some cases, surgical or laparoscopic biopsy may yield more information than ultrasound-guided core biopsy. Thus, you should carefully examine the particular situation. The needle core samples are small, and sometimes, histopathologists are not familiar with the small sample size, making it difficult for them to commit their diagnosis. Then, a wedge sample biopsy may be more helpful through a surgical or laparoscopic approach. When you cannot gain diagnosis through the first attempt, clients may not give you the second chance.
The tissue core biopsy is a sterile procedure, and the area of the biopsy should be prepared accordingly. Hemorrhage is certainly a common complication. Blood clotting test must be utilized to screen potential problems.
A skin incision is needed to make sure that a biopsy needle freely moves. The peritoneum can be penetrated by the biopsy needle rather than a deep skin incision. There are many needles in the market. It is imperative to use automatic types rather than manual types. The manual types increase the chance of complications and do not usually yield a good core sample.
For an inexperienced operator, it is a good idea to use a guide. The guide may not show the actual needle path during the procedure. However, a free hand technique has so many factors that can go wrong. It is much safer to use the guide than freehand procedure.
One should limit the number of attempts. If you cannot get a sample after 2 or 3 attempts, the procedure should be aborted. The obtained core sample should be immediately placed in an appropriate fixation fluid. In addition, care should be taken not to loose a small sample. We use a plastic cassette with sponge inserts. Both sponges are wet with the fixation fluid prior to closing, making easy to remove by histology technicians.
The area of the biopsy should be re-examined immediately after the procedure for potential bleeding. If the bleeding is suspected in next few hours, the area should be re-examined.