Page 318 - Feline diagnostic imaging

324 20 Thorax
20.1.2 Technique: Fine Needle Aspiration and syringes (if used) should be replaced if different organs
or sites are aspirated. It should be noted that ultrasound gel
As with all ultrasound‐guided biopsies, a full abdominal can create significant artifacts on the specimen slide and
ultrasound should be performed initially. This allows com- should be avoided, or cleaned prior to aspiration.
plete evaluation of the extent of the lesion, as well as visuali-
zation of possible complications, such as metastatic disease, 20.1.3 Technique: Tissue Core Biopsies
adjacent vessels, or other overlying structures. The shortest,
most direct needle path is selected which avoids vessels and Several types of biopsy devices are available (Figure 20.1). A
overlying organs. Bleeding times (if the patient is high risk spring‐fired biopsy needle is preferred over a manually
for hemorrhage) or at least a platelet count may be done powered needle, as the spring firing insures a better cutting
before most needle aspirations. The patient is sedated as nec- of the tissue and more reliable tissue sampling. A single
essary. Agents that induce panting or splenomegaly should spring device fires only the outer cutting cannula of the
be avoided. The overlying skin should be clipped and asepti- biopsy needle. The inner trocar is positioned manually
cally prepared. within the area of interest before firing the device. This is
The transducer is placed over the target organ so that it is safer in small, restricted tissues, and is much safer for use in
centered on the screen. The needle is inserted just cranial (or cats. A double spring‐fired biopsy gun automatically
caudal) to the transducer, and parallel with the plane of the launches first the inner trocar, followed immediately by the
ultrasound beam, with the bevel (concave portion of the outer cutting cannula. Very good tissue samples are
needle tip) placed toward the transducer. The needle is achieved, but the needle extends an additional 1–2 cm
angled 20–45° off the long axis of the transducer. The needle beyond the original needle tip location. A 2 cm “safety zone”
is most completely visualized when it is at a right angle to is necessary beyond the needle tip. This double spring‐fired
the sound beam. However, it should be placed close to the biopsy gun is not recommended in cats, as a sudden shock
transducer to ensure that the entire needle pathway is identi- wave generated by the gun may induce a vagal shock reac-
fied as the needle is inserted. The needle tip should be closely tion within 15–30 minutes after biopsy in cats, and possibly
watched as it enters the tissue. Small corrections or manipu- small dogs [4]. Needle sizes for core biopsies range from 18
lations of the needle can be made by the operator to ensure to 14 G, and needles for this device are disposable.
the needle follows the correct path and enters the target tis- Prior to the tissue core biopsy, bleeding times and a base-
sue correctly. The needle tip is sometimes difficult to visual- line hematocrit should be obtained. The main contraindi-
ize, especially when using smaller gauge needles or in obese cation for biopsies of any kind, including the less invasive
animals. The presence of a stylet within the needle can fine needle aspiration, is an unregulated clotting disorder.
enhance visualization, as can small back‐and‐forth motions Again, a full abdominal ultrasound exam is performed. The
of the needle. The focal zone should be placed at the region patient should be heavily sedated or placed under general
of interest to enhance visualization of the needle. anesthesia. Any sudden or violent motion could result in
Once the needle has entered the target tissue, two meth- tissue laceration and hemorrhage. The selected portion of
ods of sample collection may be used. The first involves the abdomen is prepared in a sterile fashion, and a sterile
simple aspiration of the affected area through a needle via probe cover or sterile glove is placed over the transducer.
a syringe. The needle is then withdrawn and its contents Because the probe cover can, in some instances, degrade
expelled onto a glass slide. A 6–12 cc syringe is typically the image, some operators simply cleanse the transducer
used for the aspiration. An extension set may be used surface with alcohol (based on manufacturer instructions).
between the syringe and the needle, rather than attaching No complications have been reported with this technique.
the syringe directly to the needle. This allows greater free- Alcohol is used to wet the skin surface and the best needle
dom in manipulating the needle during the procedure. The path is selected. A small skin incision is made and the nee-
aspiration technique typically works well, but can result in dle is placed just cranial (or caudal) to the transducer, and
hemodilution of the cell sample. An alternative method parallel to the plane of the ultrasound beam. The needle is
involves the use of a needle, with or without an attached inserted 20–45° off the long axis of the transducer, and is
syringe. Once the needle has been correctly placed in the closely watched as it enters the tissue. The biopsy proce-
target tissue, it is rapidly moved in and out, 5–10 times, dure may be repeated as necessary to obtain sufficient tis-
using no negative pressure [3]. The needle becomes filled sue for culture and histopathology. The same needle may
with cellular material, which is then expelled onto a slide. be used for repeated biopsies of the same organ, but should
This technique results in a smaller sample volume but con- be replaced if other organs are biopsied.
tains less peripheral blood contamination. Each procedure Immediately after any biopsy procedure, but especially
may be repeated 2–3 times to ensure diagnostic quality after a tissue core biopsy, the area should be checked for
samples. Needles should be replaced after each aspiration, hemorrhage. The patient should be checked again several