Page 215 - WSAVA2018
P. 215

WSV18-0264
GASTROENTEROLOGY / LIVER
HOW TO TAKE AND INTERPRET A LIVER BIOPSY
P. Watson1
1Department of Veterinary Medicine, University of Cambridge, UK
Introduction
The clinical should always give careful consideration to the reasons behind taking a biopsy: you take a biopsy
to give you a diagnosis, prognosis and/or guidelines for treatment. There is no clinical justification for undertaking a procedure as invasive as a liver biopsy unless it changes treatment decisions – doing it for ‘interest’ is certainly not justified. However, because the results of blood and imaging tests are non-specific in liver disease, some form of liver biopsy is usually indicated to give
a diagnosis and allow most effective treatment. The clinician must then decide the best way to perform this biopsy considering how stable the patient is, the financial resources of the owner and the relative reliability of the results obtained with different methods.
Biopsy methods
There is also little point in taking a biopsy which is not representative of the underlying disease – if the sample is too small, or from the wrong place, or only from one of a number of organs affected with disease, it may lead to the wrong conclusions being drawn and the wrong, or incomplete, treatment protocols.
Not all biopsies are created equal. The options for liver
biopsy are:
· Fine needle aspiration (FNA) cytology – not strictly a biopsy but worth considering here as a potential alternative to more invasive biopsies
· Ultrasound-guided trucut biopsy
· Wedge biopsy – at laparotomy or laparoscopy.
Before undertaking any biopsy except FNA the clinician MUST check coagulation times and platelet count.
This is even more important in cats than dogs because cats with liver disease have a higher prevalence of coagulopathies than dogs. This may be because of
the high prevalence of biliary tract disease in cats resulting in fat malabsorption and vitamin K deficiency. This problem is compounded if they have concurrent inflammatory bowel disease and/or chronic pancreatitis causing exocrine insufficiency. At least a whole blood clotting time and platelet count on the feathered edge of a blood smear should be performed prior to canine and feline liver biopsies, and there is a rational argument for parenteral vitamin K treatment for 12-24 hours prior to biopsy in ALL cats.
FNAs: beware becoming ‘liver FNA happy’ for fear
of false diagnoses and wasting the client’s money! FNA of the gall bladder has a primary indication in the
diagnosis of ascending biliary tract infections in dogs and cats – in fact, it is the best (perhaps only effective) way of doing this and is much more sensitive than liver culture or histopathology of a liver biopsy. It allows bile cytology and culture and selection of an appropriate antibiotic based on the results of culture and sensitivity. So, if ascending cholangitis is a differential, a careful bile aspirate should be performed. However, FNAs for anything else can be misleading: this is because of
the ‘selective’ nature of aspirates – only things which
will aspirate up a needle will be harvested and there
is no anatomical information, so this is a very poor way of diagnosing diffuse liver disease such as chronic hepatitis, which is the commonest liver disease in dogs. There is a moderate indication in suspected hepatic lymphoma and feline hepatic lipidosis but even those cases can be misleading. Willard et al 1999 reported four cats in which fine-needle aspirate cytology suggesting hepatic lipidosis was misleading – in three cases,
there was cholangiohepatitis on histology and in one case there was lymphoma. This is not to say that FNA does not have an important place in the diagnosis of feline hepatic lipidosis – cats in the acute phase of the disease on presentation are rarely well enough to have a general anaesthetic and more invasive biopsies. A rapid diagnosis with FNA allows initiation of supportive therapy and tube feeding. However, if the cat fails to respond appropriately after several days of feeding, consideration should be given to obtaining a liver biopsy.
Your Singapore, the Tropical Garden City
  · Ultrasound-guided trucut biopsies: these are less invasive than a laparotomy but do carry some risk – particularly of haemorrhage, so the dog or cat needs monitoring closely for about 12 hours after the pro- cedure. Particular care should be taken in cats and the semi-automatic biopsy guns should be avoided
in this species as they can cause significant mortality. Ultrasound-guides biopsies can be less representa- tive than wedge biopsies – probably because of the small size of the sample. This problem is more serious in dogs than in cats with chronic liver disease. Cole
et al 2002 compared the diagnosis made on ultra- sound-guided needle biopsies with wedge biopsies of the liver in 98 dogs and 26 cats and found the mor- phological diagnoses agreed only 48% of times.
· Wedge biopsies at laparotomy or laparoscopy. These have the advantages of being more reliable diag- nostically and also of allowing concurrent pancreas and intestinal biopsies to be taken to rule in or out concurrent pancreatitis and / or inflammatory bow-
el disease. A feeding tube can be placed and the patency of the bile duct checked – all very useful. However, there is also a significant morbidity asso- ciated with these procedures – particularly with the concurrent gut biopsies – and a small but important risk that the cat may die as a result of complications of surgery. The risk-benefit balance therefore has to be carefully discussed with the owner before the method of biopsy is decided upon.
        213
            

































































   213   214   215   216   217