Liver Biopsy

Liver biopsy can be performed safely even when ultrasonographic equipment is not available. Complications associated with liver biopsy are rare.

Liver Biopsy

Indications

• To confirm or rule out liver disease. Even when the activity of liver-specific enzymes is significantly increased in the serum, primary liver disease may not be present.
• To supply an etiologic diagnosis of liver disease. An etiologic diagnosis is often not possible because many hepatic diseases produce similar histological changes. Pyrrolizidine alkaloid toxicosis, cholangiohepatitis, neoplasia, and fatty liver disease, however, can often be diagnosed by liver biopsy.
• To provide tissue for bacterial culture
• To determine the prognosis of a horse with liver disease
• To determine the chronicity of disease
• To determine progression or resolution of liver disease (with serial biopsies)

Contraindications

• Horses with advanced cirrhosis may have increased prothrombin and whole-blood clotting times. Coagulopathy is often claimed to be a contraindication for liver biopsy. Significant hemorrhage after liver biopsy is rare, however, even in horses with evidence of a coagulopathy.
• Suspicion of liver abscesses (to avoid bacterial contamination of the thorax and abdomen)
• Concurrent pulmonary disease for which lung biopsy is contraindicated (see section on lung biopsy) because the biopsy needle may pass through lung

Materials

• Sedation is optional, but restraint should be sufficient to prevent movement during the procedure.
• #15 blade and sterile gloves
• 5 - 10 mL local anesthetic solution
• 12- to 14-gauge biopsy needle (Vim-Silverman, Tru-Cut style, Menghini, or Monopty® are good choices)
• Ultrasonographic equipment for selection of biopsy site (optional) Ultrasonographically guided needle biopsy is useful for diagnosis of focal liver disease.
• 10% formalin and bacterial transport medium

Procedure

• The procedure is performed on the right side of the horse
• When ultrasonography is not available to identify the optimum site for liver biopsy, a common site for biopsy is the 14th intercostal space. To find this site, first find the 17th intercostal space (i.e. the last intercostal space) and count forward on a line drawn from the tuber coxae to the point of the shoulder (Fig. 21.1). When sites cranial to the 14th intercostal space are used, lung is more likely to be penetrated.
• After surgically preparing the biopsy site, the body wall is infiltrated with local anesthetic solution, and the skin is stabbed with a #15 blade near the cranial edge of the neighboring rib (to avoid the intercostal artery located at the caudal edge of each rib).
• The biopsy needle is inserted and directed at a slightly oblique angle (30°) craniad and ventrad, aiming for the opposite elbow (Fig. 21.2). If pushed slowly, the biopsy needle can be felt to pass through the diaphragm and enter the liver. The gross appearance of the tissue obtained confirms that a sample of the liver has been collected.
• Tissue is removed from the biopsy needle and placed in formalin, and if bacterial cholangiohepatitis is suspected, another sample of tissue is collected and placed in a bacterial transport medium.
• The stab incision can be closed with a suture or allowed to heal by second intention.

Figure 21.1. A common site for blind liver biopsy is the 14th intercostal space near a line drawn from the tuber coxae to the point of the shoulder.

Figure 21.2. The biopsy needle is inserted and directed at a slightly oblique angle (30°) craniad and ventrad aiming for the opposite elbow.  

Interpretation

A histopathologist should interpret the biopsy, but a brief histological description of some liver diseases is presented.

• Lesions can sometimes be seen during gross examination of a liver biopsy sample (Fig. 21.3).
• Most diseases of the liver are diffuse, and tissue obtained by biopsy is usually representative of the condition of the liver. Neoplasia is one disease that could be missed by biopsy performed without ultrasonography, but for most liver diseases, biopsy results and necropsy findings are closely correlated.
• Pyrrolizidine alkaloid poisoning, one of the most common causes of liver disease in the horse, causes typical changes in the liver: hepatomegalocytosis, proliferation of bile ducts, and periportal fibrosis.
• The bile ducts of horses with cholangiohepatitis are distended with purulent debris, and surrounding tissue is infiltrated with neutrophils. Aerobic or anaerobic bacteria can often be cultured from the biopsy specimens.
• Histopathological examination of a liver biopsy has greater prognostic value than other tests for determining survival of horses with liver disease.

Figure 21.3. Lesions may be seen during gross examination of a liver biopsy sample.

Complications

• Complications are rare if contraindications are not ignored. Owners should be warned, however, of potential complications.
• Hepatic hemorrhage. For horses with clinicopathological evidence of a coagulopathy, transfusion of two liters of blood may prevent hemmorhage. Significant hemorrhage after liver biopsy is rare, however, even in horses with evidence of a coagulopathy.
• Pulmonary hemorrhage. Because the biopsy needle may pass through lung, severe pulmonary hemorrhage may occur, especially if the horse has recurrent airway obstruction.
• Biopsy of other organs. When this occurs, most commonly it is the lung that is biopsied. Lung tissue is easily identified by gross examination. Intestinal contents are occasionally found in the biopsy needle. If intestinal contents are retrieved, the biopsy is repeated at another site using another sterile biopsy instrument, and as a precaution, broad-spectrum antimicrobial drugs can be administered for several days.

Suggested Readings

Pearson EG, Craig AM. The diagnosis of liver disease in equine and food animals. Mod Vet Pract 61: 233-237, 1980.  - PubMed -

Pearson EG. Liver disease in the mature horse. Equine Veterinary Education 11:87-96, 1999.

Durham AE, Smith KC, Newton JR, Hillyer MH, Hillyer LL, Smith MR, Marr CM. Development and application of a scoring system for prognostic evaluation of equine liver biopsies. Equine Vet J 35:534-540, 2003.  - PubMed -