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61 Imaging in Hepatobiliary Disease 675

technique is being successfully used in dogs and cats and When obtaining samples, the most important guide-
VetBooks.ir can provide a rapid and accurate diagnosis with excellent lines are to use the shortest distance and the safest path
to reach the site of interest. The needle should not pass
anatomic resolution. In dogs with liver masses, MR
imaging findings have also been successful in differenti-
organ and for both FNA and tissue‐core samples, it is
ating benign and hepatic lesions. through more than one body cavity or more than one
important to visualize the needle tip as it is advanced
into the tissue, keeping the entire needle length visible
Image‐Guided Sampling within the plane of the ultrasound beam. Accurate nee-
dle placement is usually easier using a curvilinear (or
Although diagnostic imaging provides useful information, micro‐convex) transducer. For superficial lesions, linear
the imaging features of canine and feline hepatobiliary dis- transducers have the advantage of superior near‐field
ease are rarely specific for a single disease process. Despite resolution, but needle placement may be more challeng-
the potential offered by newer techniques such as con- ing. 1” or 1.5” 20–22 ga standard injection needles are
trast‐enhanced ultrasound, CT and MRI, in most cases it most commonly used for FNA, with 2.5” or 3.5” spinal
is still not possible to definitively characterize the underly- needles occasionally used for sampling deeper lesions.
ing disease process or to differentiate benign from malig- For tissue‐core biopsies, either manual or automated
nant disease from the imaging appearance alone. biopsy devices may be used. A 14, 16 or 18 ga needle
Obtaining samples of material for cytology and/or histo- (depending on the size of the patient and of the liver) and
pathology is therefore important in providing additional a 2 cm tissue sample notch are usually selected.
information and, in many cases, a definitive diagnosis. Depending on the patient’s clinical status and the tissue
The most commonly used image‐guided sampling being sampled, a coagulation profile is not usually
techniques are percutaneous ultrasound‐guided aspira- required before obtaining FNAs; however, it is strongly
tion and tissue‐core biopsy. These well‐established tech- recommended prior to tissue‐core biopsy.
niques are routinely used in dogs and cats, and are Although many conscious patients will tolerate ultra-
considered safe and minimally invasive. Fine needle aspi- sound‐guided FNAs, sedation is recommended and gen-
ration (FNA) is cheaper, easier and has fewer potential eral anesthesia is indicated for patients undergoing
complications than tissue‐core biopsy. However, cyto- tissue‐core biopsy. When obtaining FNAs, the skin over-
pathologic (FNA) and histopathologic (core biopsy) lying the aspiration site should be clipped and cleaned
diagnoses from the same tissue do not always agree. prior to sampling; ultrasound gel can confuse the cyto-
FNAs inevitably result in disruption of the normal struc- logic interpretation and should be avoided. For a tissue‐
tural relationship between cells within a tissue and are core biopsy, aseptic preparation is required. Ultrasound
therefore most useful in diagnosing diseases that can be gel may be used, but should be sterile.
identified from individual cells (e.g., lymphoma) and in Serious complications associated with FNAs are rare, but
differentiating between inflammatory, neoplastic, and include hemorrhage, tumor seeding, and, following gall-
degenerative/necrotic change. In conditions where pres- bladder aspiration, bile leakage and potential peritonitis.
ervation of tissue architecture is more important, for The risk of hemorrhage is increased with tissue‐core biopsy;
example vascular disorders and chronic hepatopathies, a however, although small amounts of free fluid are not
tissue‐core biopsy is more likely to provide useful diag- uncommon post biopsy, in patients with normal coagula-
nostic information. tion status any bleeding should be self‐limiting.