Page 911 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

886 CHAPTER 5

VetBooks.ir of histopathology; therefore, approximately 2–4 cm where possible, that biopsies are collected from at
least two different sites or, at least, from slightly dif-
of biopsy material is collected in total where possible
(Fig. 5.15). Biopsy specimens should be placed in
Examination of liver biopsy specimens is the most
10% buffered formalin for histopathology, although ferent angles at the same site.
where suspicions of bacterial cholangiohepatitis exist likely means by which the aetiology of liver disease is
then culture of fresh biopsy material might also be identified, although this will still prove to be evasive
useful given the caveat that even successful culture in the majority of cases. Certain types of liver dis-
might not necessarily comprise all bacterial species ease such as septic cholangiohepatitis, pyrrolizidine
present. alkaloid toxicosis (Fig. 5.16), neoplasia and severe
It is a commonly stated dogma that liver disease haemosiderosis may well provide characteristic histo-
in horses is diffuse and it is generally assumed that pathological findings, although the majority of clini-
collection of a biopsy from any site is likely to be rep- cal cases of liver disease examined in equine practice
resentative of the underlying hepatopathy. Although will reveal patterns of pathology that are not specific
this generally appears to be the case, variation can be for any precise causation. One should also be mind-
seen in biopsies taken from different sites of the same ful that minor pathological insults are commonly
liver in up to 30% of cases, albeit in most cases the encountered in horses showing no clinical or clinico-
variation is mild. Furthermore, even at a microscopic pathological evidence of liver disease, including mild
level hepatic pathology is very rarely genuinely dif- periportal lymphoplasmacytic infiltrates and mild to
fuse. For example, fibroplasia tends to preferentially moderate haemosiderin accumulation in hepatocytes
have a porto-portal pattern in most equine liver dis- and Kupffer cells. Despite these diagnostic limita-
ease cases. However, adjacent portal tracts may be tions, there are further clinical benefits from exam-
variably affected (intrabiopsy variability) and, fur- ining the biopsy specimens in addition to confirming
thermore, a very different impression of the degree that liver disease is definitely present, even if the pre-
of fibrosis can be made from two adjacent biopsies cise aetiological factors are often elusive.
(interbiopsy variability), depending on the relative Alongside neoplasia, megaolcytosis and extensive
proportion of acinar margins that are included in necrosis, marked periportal and bridging porto-
the specimen. Thus, it is generally recommended, portal fibrosis is the most prognostically concerning

5.15 5.16
F

BH

H

M

Fig. 5.15 Liver biopsy specimens of mixed individual Fig. 5.16 Biopsy specimen demonstrating typical
lengths collected from the same horse (approximately signs of pyrrolizidine alkaloid toxicosis including
33 mm of biopsy specimens in total). fibrosis (F), megalocytosis (M) and biliary hyperplasia
(BH), with an additional finding of orange granular
haemosiderosis (H).