Page 907 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

882 CHAPTER 5

VetBooks.ir Although clinical usefulness of these parameters has become visible immediately ventral to the border
of the lung. On the left side, the liver can typically
been established in the horse, limited availability
of testing has greatly restricted their employment.
ately caudal to the heart and cranial to the spleen and
Measurement of plasma ammonia concentration is only be imaged for 2–4 intercostal spaces immedi-
a useful means of confirming HE, although sample stomach, between the 5th and 9th intercostal spaces
handling is crucial. Plasma ammonia concentration (Fig. 5.9). Generally, a much larger image area
tends to increase in vitro in blood samples, primarily extending for between 3 and 8 intercostal spaces is
due to ammonia release from erythrocytes but also found on the right side, typically anywhere between
from deamination of plasma proteins. Therefore, the 6th and 16th intercostal spaces (Fig. 5.10).
the plasma should be separated from the sample as The normal liver has a relatively hypoechoic
soon as possible and kept chilled until tested. Even homogeneity, interrupted by anechoic blood ves-
when promptly separated and chilled, it is advised sels, typically <9 mm in diameter in the superficial
that samples are tested within 4 hours of collection regions, although larger vessels are sometimes seen
to avoid possible spurious increases. Despite the cen- in ponies due to the ability to image relatively deeper
tral role of the liver in maintaining glucose supply hepatic tissue. The large central caudal vena cava is
for the circulation, hypoglycaemia is rarely seen in
horses with hepatic failure. In fact, hyperglycaemia
is commonly associated with severe illness probably
as a result of insulin resistance. Occasional cases of 5.9
hepatic neoplasia have been reported with profound
intermittent hypoglycaemia. LICS8
Haematology rarely gives specific diagnostic DIAPH
help in cases of liver disease. Although leucocytosis
might reflect an inflammatory liver disease, systemic LUNG LIVER
inflammation can result from non-inflammatory
liver disease as discussed above. Anecdotally, relative
neutropenia and lymphocytosis are also sometimes
observed in horses with liver disease. Erythrocytosis SPLEEN
may reflect dehydration in especially sick liver dis-
ease cases, although this is also noted in some neo-
plastic and non-neoplastic hepatopathy cases, in the
absence of dehydration. 5.10

Ultrasonographic assessment of the liver
Although hepatic tissue is typically only about 3 cm
deep to the skin surface and easily imaged ultra-
sonographically, the majority of the equine liver is LUNG LIVER
masked by the echo-reflective lungs. Therefore, a
thorough ultrasonographic evaluation of the equine COLON
liver is impossible as there will always be a large por-
tion of the liver that cannot be imaged. The most
reliable way to find the liver ultrasonographically
is to place the ultrasound transducer over the tho-
racic lung field to obtain the characteristic and easily
recognisable echo-reflective gliding pleural surface Figs. 5.9, 5.10 Ultrasonographic images of the
with reverberation artefact. As the transducer is then normal liver as seen via the left 8th intercostal space
moved in a ventral direction, the liver image will (5.9) and the right 12th intercostal space (5.10).