Page 908 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Liver disease 883

VetBooks.ir often seen from the right side in ponies and should 5.11
not be confused with a cystic structure. Very local-
ised hyperechoic (without acoustic shadows) signals
are commonly associated with blood vessels as a
result of fibrous perivascular connective tissue and
acoustic enhancement artefact. Bile ducts cannot
normally be visualised. In larger blood vessels, flow
can often be visualised in real time with standard
B-mode ultrasonography, although Doppler can be
used to establish active blood flow where doubt exists
over the identity of dilated vessels (Fig. 5.11).
The normal hepatic image from the right side
is approximately triangular in shape with a sharply
angled caudoventral edge (Fig. 5.9). It has a con-
vex surface adjacent to the diaphragm laterally, and
a concave surface against the hyperechoic colonic
image medially. When imaged from the left side a
biconvex shape is often seen (Fig. 5.10). It should
not be confused with the caudomedially adjacent
spleen, which has similar ultrasonographic archi-
tecture, but is significantly more hyperechoic than
the liver and has fewer blood vessels. In cases of
hepatic atrophy, the left lobe of the liver can be
imaged more consistently than the right. Rarely,
hepatopathy cases are seen in which no liver tis-
sue can be imaged ultrasonographically and lapa- Fig. 5.11 An enlarged intrahepatic vessel confirmed
roscopy can then be used to visualise the liver and to be a blood vessel by active flow detected using
guide biopsy collection. colour flow Doppler.
As mentioned above, there is a limited ultraso-
nographic view of the equine liver, suggesting that
the technique is inherently insensitive for detecting the liver per se. Typically around 10–12 cm of hepatic
focal hepatic diseases such as abscesses, neoplasia or tissue can be imaged projecting caudoventrally from
cysts. However, even in cases of diffuse liver disease, the expiratory border of the lung in the right 13th
ultrasonographic images are frequently unremark- intercostal space, although it is occasionally the case
able. Although the majority of cases of hepatopathy that no imageable hepatic tissue can be seen at all
do not have discernible ultrasonographic abnormali- on the right side of normal horses. The peripheral
ties, images classified as abnormal have a high speci- margins of the liver should demonstrate acute angu-
ficity for the presence of significant liver disease and lation and if smooth or rounded this does support
are associated with poorer outcomes. Fibrosis, hae- hepatomegaly and swelling. The ability to image
mosiderosis and lipidosis may all be associated with several dilated (>9 mm) blood vessels in the periph-
a diffuse increase in echogenicity of hepatic tissue, eral hepatic images may be associated with portal
but this is largely a subjective judgement, albeit com- hypertension and hepatic fibrosis. Single or multifo-
parison with splenic echogenicity (normally spleen cal small (<5 mm) hyperechoic foci are occasionally
is significantly more echogenic than the liver) on the encountered within hepatic images in the absence of
left side can be useful. Hepatomegaly or atrophy is further changes and have become known as a ‘starry
also subjective as the area of liver imaged depends sky’ pattern (Fig. 5.12). Such findings are rarely of
as much on the size of the lung fields, as the size of pathological significance.