Liver disease in the horse: diagnostic aids and differential diagnosis
The most common clinical signs of hepatic insufficiency in horses are weight loss, hepatic encephalopathy, icterus and colic.
The architecture of the normal equine liver should be relatively uniform and appear less echogenic than the spleen. The walls of portal veins are more echogenic than hepatic veins and often are seen as short, white parallel lines in the parenchyma (Figure 3).
The biliary ducts are not normally seen in healthy horses, and the common bile duct cannot be imaged transabdominally in adult horses.
Lack of notable size or architectural ultrasonographic changes in the liver do not rule out the possibility of significant disease. If the liver is small or there are focal ultrasonographic changes, ultrasonography is useful for guiding biopsy instruments into the liver.
A liver biopsy often provides the most specific information for an etio logic diagnosis. The procedure is performed in the standing horse at the right 12th to 14th intercostal space, at the intersection of a line drawn from the tuber coxae to a point midway between the elbow and the point of the shoulder. Sedation may be needed.
Although a liver biopsy can be obtained solely by using the previously mentioned anatomical landmarks, an ultrasound-guided biopsy often significantly increases the chances of obtaining a useful sample.
The skin overlying the area to be sampled should be clipped, aseptically prepared and a local-acting anesthetic injected subcutaneously. A stab incision is then made with a No. 15 scalpel blade. A Tru-Cut (Baxter-Travenol, St. Louis) biopsy instrument is inserted and directed craniad and ventrad through the diaphragm into the liver.
Semi-automatic biospy instruments and automatic biopsy guns are helpful for a quick and accurate liver biopsy.
Samples should immediately be placed in formalin for histopathologic evaluation and in transport media for culture.
Precautions to consider prior to performing the procedure include the risk of hemorr hage, pneumothorax and peritonitis from bile leakage and colon or abscess puncture, and spread from infectious hepatitis.