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20

Thorax
Martha M. Larson

Department of Small Animal Clinical Sciences, Virginia-Maryland College of Veterinary Medicine, Virginia Tech, Blacksburg, VA, USA

20.1 Ultrasound-Guided Biopsy/ Ultrasound‐guided fine needle aspiration involves the
Aspiration use of a small‐gauge needle (20–25 G) placed in the area of
interest, with cells subsequently aspirated or forced into
20.1.1 Introduction the needle. The larger size needles may be needed for aspi-
ration of exudative or thick fluids. Spinal needles (up to
Ultrasound‐guided biopsy has become a well‐recognized 3.5 in.) can be used when increased depth requires a longer
and widespread technique used by most people performing needle. Larger bore needles (18–14 G) are used for core
ultrasound examinations. With ultrasound guidance, the biopsy. These biopsies may be performed with manual
biopsy needle is visualized, and manipulated as necessary, Core needles, semiautomated or automated gun devices.
to enter the target organ or lesion. The passage of the nee- Larger tissue samples are retrieved with a core biopsy com-
dle can be continuously monitored. Adjacent vessels or pared to fine needle aspiration biopsy, and a histopatho-
overlying structures can be avoided, and specific lesions logic diagnosis may be achieved.
can be biopsied. Thoracocentesis can be performed with The choice of aspiration biopsy versus core biopsy
ultrasound guidance. Ultrasound‐guided biopsy can reduce depends on the patient and disease process. Fine needle
the risk and expense of surgical exploratory surgery. aspiration may be performed first, as this procedure
Ultrasound‐guided biopsy involves constant visualiza- involves minimal risk, does not require general anesthesia,
tion of the needle tip as it enters the target organ. It may be and is quick and inexpensive. However, the resultant
done free hand or with the use of a biopsy guide. These sample frequently is insufficient for a diagnosis [1,2]. Fine
guides are needle‐holding devices which attach to the needle aspirations are most helpful in diseases in which a
transducer. They insure that the needle, when placed cor- single cell can be diagnostic, such as tumor masses, or
rectly within the attached guide, will remain within the when a small sample for culture is needed. Some diffuse
plane of the ultrasound beam. Biopsy software allows visu- diseases, such as hepatic lipidosis, may also be diagnosed
alization of biopsy pathway guidelines projected electroni- on a needle aspirate. Core biopsies will result in larger, and
cally on the monitor. Biopsy guides and software can be often more diagnostic, tissue samples. However, tissue
safer to use, especially for an inexperienced operator. Even trauma and the possibility of hemorrhage are greater with
with these guides, however, some needles will still bend this technique, and it requires heavy sedation or general
and be displaced out of the scan plane. These devices can anesthesia.
sometimes be awkward to manipulate, especially in small For any organ, ultrasound‐guided biopsies are operator
or confined locations. With experience, freehand biopsy dependent, and require practice to acquire the skills to per-
technique may become more convenient. In freehand tech- form them safely and accurately. Cadavers may be used for
niques, the needle is placed without a needle guide, by such practice. In addition, tissue phantoms can be pur-
hand, at an oblique angle to the long axis of the transducer. chased, or home‐made with gelatin or agar which simu-
The operator has more flexibility to make fine adjustments, lates tissue echogenicity. Olives, grapes, and fluid‐filled
and can manipulate the needle while watching it enter the glove tips can be placed within the phantoms to allow
target organ. aspiration practice.

Feline Diagnostic Imaging, First Edition. Edited by Merrilee Holland and Judith Hudson.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.