Liver Biopsy in Small Animals

Liver biopsy is the gold standard for diagnosis of liver disease.

Hepatic core needle biopsies (especially 18-gauge) collected under ultrasonographic guidance may yield samples too small and fragmented for accurate diagnosis because of a lack of representative acinar units (at least 15 portal triads should be sampled). Furthermore, needle biopsies are usually collected only from the more safely sampled left-side liver lobes, which may miss lesions differentially affecting liver lobes (eg, cholangiohepatitis in cats).

Blind needle biopsies done without ultrasonographic guidance are hazardous and ill advised. Laparoscopic biopsy using cup forceps and wedge surgical biopsies are preferred, because samples of adequate size can be easily and safely acquired from multiple liver lobes. This strategy ensures that enough tissue and samples from diverse locations will provide accurate disease representation. These methods also permit assessment of the gross appearance of the liver.

Notably, laparoscopic methods are not recommended when disease of the common bile duct or gallbladder is suspected that may necessitate a decompressive biliary procedure, cholecystectomy, choledochotomy, cholelith removal, or cholecystoenterostomy (ie, cholecystoduodenostomy, cholecystojejunostomy).

Liver biopsy should always be done even if an obvious biliary abnormality is the predominant disease process, because underlying histologic liver lesions will guide recommended treatment. Liver sections distant to the gallbladder should be sampled to avoid collection of peribiliary glands in gallbladder-adjacent tissue that may be misconstrued as malformative bile duct structures. Sections from distant liver sites will also determine the breadth of liver lesions unassociated with local cholecystic inflammatory reactions.

It is also important to biopsy grossly normal liver when focal lesions are identified. This practice achieves the following:

1. ensures characterization of normal liver histology

2. determines whether an underlying liver disease coexists

3. investigates histology of liver distant to the gallbladder in animals undergoing cholecystectomy

4. provides multiple liver lobe samples needed to confirm suspected microvascular dysplasia (MVD) (because this lesion is variable among liver lobes)

Routine biopsy evaluation should include the following:

• examination of a cytologic imprint

• Gram stain, if suppurative or pyogranulomatous inflammation is cytologically detected

• routine H&E staining and interpretation

• staining with a reticulin stain, which discloses the supporting scaffolding of the hepatic cords and defines regions of parenchymal collapse or injury

• staining with Masson trichrome to confirm presence and severity of fibrillar connective tissue deposition

• staining with Prussian blue to identify iron retention in Kupffer cells (fixed macrophages) and rarely in hepatocytes (this stain helps confirm regions of lobular involvement in inflammation, Kupffer cell activation, rare hemochromatosis [iron accumulation predominantly in hepatocytes])

• rhodanine stain for copper, which confirms and can be used to quantify copper with digital scanning of rhodanine-stained sections

• aerobic and anaerobic bacterial cultures of liver and bile

• if needed, quantification of liver metals (copper, iron, and zinc concentrations, because these values can help evaluate risk of oxidative injury and need for zinc supplementation)

Metal quantification is best done by atomic absorption spectroscopy, considered the gold standard for copper tissue quantification, the validation method for digital copper quantification. Copper values discordant with rhodanine-stained copper distribution and copper analysis by digital quantification have been repeatedly encountered with copper quantified using inductively coupled plasma mass spectrometry analysis (samples analyzed by three different laboratories). A tissue sample (formalin fixed) should be reserved for other special case-specific studies such as special immunohistochemical stains or for PCR assay for infectious agents.

Before biopsy, bleeding tendencies should be evaluated by meticulous review of history, physical examination, blood smear (to confirm platelet count ≥ 100,000 platelets/mcL), routine coagulation tests (prothrombin time [PT], activated partial thromboplastin time [aPTT]), von Willebrand factor (VWF) activity in high-risk breeds, and buccal mucosal bleeding time (BMBT). Routine coagulation assessments have low reliability to detect bleeding risk, the BMBT being more relevant when performed immediately before a biopsy procedure. Animals with suspected bleeding tendencies or with jaundice should be treated with vitamin K₁ (0.5–1 mg/kg, SC or IM, repeated at 0, 12, and 24 hours before tissue sampling).

If BMBT is > 5 minutes and a liver biopsy is considered diagnostically imperative, fresh frozen plasma transfusion is indicated with reassessment of BMBT to assess achieved coagulative effect.

Administration of desmopressin acetate (0.3–1 mcg/kg diluted in saline) also acutely assists in controlling excessive bleeding. Desmopressin increases plasma VWF (2-fold above baseline) within 1 hour and plasma activity of factor VIII; however, the effect is short-lived.

Limitations in the utility of desmopressin injections include the following: it can only be used once as it depletes preformed VWF and although desmopressin can initiate hemostatic effect in dogs with type 1 VWF deficiency (partial quantitative deficiency), it cannot arrest bleeding due to a qualitative VWF defect or complete VWF deficiency. Desmopressin injection has also been used on an emergency basis during liver biopsy to arrest excessive bleeding. The mechanism of this response is likely beyond simple release of VWF monomers and remains incompletely clarified.