Page 687 - Clinical Small Animal Internal Medicine

60 Approach to the Patient with Liver Disease 655

Cytologic and Histopathologic Evaluation to an underlying disease rather than a primary diagnosis,
VetBooks.ir in Liver Disease this would place important limitations on cytology as a
sole means of diagnosis. With diffuse or focal neoplastic
The results gained from diagnostic imaging and clinical
pathology testing do not typically provide a definitive disease, aspirates can prove useful; for example, a diag-
nosis of lymphoma may alleviate the need for a biopsy.
diagnosis in patients with liver disease, except in cases However, this is not the case in all situations; the
such as CPSS. The gold standard for diagnosis in these differentiation of nodular hyperplasia and hepatoma is
patients is usually histopathologic evaluation of a liver not possible cytologically. In addition, the performance
biopsy. The liver biopsy can provide a definitive diagno- for canine inflammatory liver diseases is generally poor.
sis in some situations, for example neoplasia. In other This relates to both the importance of liver architecture
cases, while a specific diagnosis may not be made, the in the categorization of the diagnosis (e.g., chronic
biopsy provides important information about the patho- hepatitis versus cirrhosis) and the chances of missing
logic reaction pattern observed, including the location of inflammatory cells where there are areas of fibrosis.
lesions, cell types involved, and the chronicity of the Occasionally, infectious agents such as histoplasmosis
changes. This information is invaluable in guiding thera- can be diagnosed by fine needle aspiration.
peutic intervention and providing prognostic informa- Overall, the clinician must be aware of the limitations
tion. In addition, follow‐up biopsies offer an important of fine needle aspirates of liver parenchyma and regard
guide to the clinician when assessing the response to them more as a contributor of information rather than
therapy. Cytologic evaluation of samples may be consid- providing a definitive diagnosis in most situations. The
ered in some situations and is discussed below. In gen- main advantages are the safety aspects in high‐risk
eral, liver histopathology offers significant diagnostic patients and the general requirement for only limited
advantages over cytologic samples.
sedation. They can also be performed quickly, contribut-
ing to patient planning and even a final diagnosis in some
Cytologic Evaluation cases.
It is possible to gain cytologic samples from liver patients Cytologic evaluation of ascitic fluid in combination
by performing percutaneous ultrasound‐guided fine with analysis of the total protein content and cell count
needle aspiration of liver parenchyma or bile by chole- allows determination of the nature of the ascites, for
cystocentesis. Percutaneous aspiration of ascitic fluid example whether it is a transudate, modified transudate
can also provide useful information. These techniques or exudate. In general, accurate categorization of the
are minimally invasive and are associated with a low risk ascites aids in diagnostic planning by narrowing
of complications. The clinician should exercise caution down the potential differentials considered in a case. For
when approaching patients with hemostatic disorders, example, demonstration of an exudate with a bilirubin
although the risk is far less with a fine needle aspiration concentration greater than twice that of the serum would
compared to liver biopsy. suggest bile peritonitis and should prompt surgical inter-
In general, the indications for fine needle aspirates of vention. More frequently with liver disease, a modified
hepatic parenchyma are the same as those outlined later transudate is obtained, resulting from portal hyperten-
for liver biopsy. However, the main disadvantage of fine sion and increased hepatic lymph leakage.
needle aspirates and cytologic evaluation is the limited Bile cytology can also provide important information
diagnostic accuracy of this approach. The sample size where clinical signs are suggestive of cholestasis or gall-
gained provides a limited number of cells to evaluate, bladder abnormalities are detected ultrasonographically.
hemodilution may cloud interpretation and in addition, These samples can be gained by cholecystocentesis
no morphologic information about the lesion is pro- either percutaneously by ultrasound guidance or directly
vided, as it is with histopathology. during laparoscopy or laparotomy. The finding of bacte-
Studies that have compared results gained with fine rbilia and/or neutrophils within the bile supports a diag-
needle aspiration and histopathology have generally nosis of bacterial cholecystitis, or cholangitis if there is
shown poor concordance rates. One study evaluated histopathologic evidence to support hepatic changes. In
56 dogs and 41 cats and showed agreement between fine addition to cytologic evaluation, anaerobic and aerobic
needle aspirates and histopathology in approximately bacteriologic culture of bile should be performed. In the
30% of dogs and 50% of cats. The greatest agreement was author’s experience, bacteria are evident within bile far
seen with vacuolar hepatopathies, largely accounting for more frequently than inflammatory cells and occasion-
the higher accuracy in cats. However, this category also ally provide evidence of a bacterial etiology in patients
had a high rate of misdiagnosis as the primary underly- where bile culture proves negative due to antibiotic
ing lesion was missed on cytologic examination in many administration. In other patients, bacterial culture may
cases. Since hepatic lipidosis in cats is frequently a sequel be positive in the absence of any cytologic abnormalities.