In patients with known or suspected liver disease, obtaining a biopsy sample is often indicated. Liver samples may be obtained by a variety of techniques.1-4 Surgical biopsy allows the whole liver to be visually inspected and palpated, providing an ideal opportunity to obtain biopsy samples of focal lesions for histologic examination, culture and antimicrobial sensitivity testing, and metal analysis. Surgical biopsy also provides a larger tissue sample for a more complete histologic review and allows the veterinarian to examine the biopsy site for adequate hemostasis.2 This article features guidance on when and how to perform a surgical hepatic biopsy.
The indications for performing a liver biopsy include substantially or persistently increased liver enzyme activities or serum bile acid concentrations, hepatic hyperbilirubinemia, generalized changes in hepatic ultrasonographic echogenicity, unexplained hepatomegaly, or the presence of solitary or multiple focal lesions within the hepatic parenchyma.1 Liver biopsy is particularly important when the results of biochemical testing and advanced imaging modalities such as ultrasonography or scintigraphy are not adequate to establish a diagnosis. Additionally, histologic information can be combined with an already determined diagnosis to tailor specific treatment protocols, evaluate the response to therapy, and determine the prognosis. Specific indications for a surgical biopsy include microhepatia, a hepatic abscess or cyst, or a lesion that is difficult to localize on ultrasonographic examination.1 In addition, excisional biopsy of a pedunculated or solitary mass may provide treatment opportunities.
SELECTING AND COMPARING LIVER BIOPSY METHODS
Liver samples may be obtained percutaneously by blind or ultrasound-guided biopsy or surgically by laparoscopy or celiotomy.1-4 Selecting the appropriate method is determined by the size of the liver, the type and size of the lesion, and the patient's size and overall health.1,2
Biopsy samples from unstable patients or from patients with severe coagulopathy are best obtained by percutaneous means such as fine-needle aspiration or Tru-Cut biopsy, particularly if diffuse disease is suspected.1 However, both of these methods are significantly inferior to wedge biopsy, potentially affecting an accurate diagnosis.5-8 Cytologic examination of samples obtained by fine-needle aspiration cannot provide information about tissue architecture and may be nondiagnostic for lesions that exfoliate poorly. The correlation between cytologic examination of fine-needle liver aspirates and histologic examination of hepatic biopsy samples is poor; diagnostic correlation of samples was 30% in dogs and 51% in cats in one study and 29% in multiple species in another study.5,6 In fact, cytologic and histologic examinations have a significantly lower correlation in hepatic tissue than all other tissues studied, including cutaneous, subcutaneous, nasal, osseous, lymphatic, splenic, gastrointestinal, cerebral, and ocular tissues.6
Sample size and quality are also variable when ultrasound-guided tissue core biopsy samples are obtained. In one study, only 77% of intended liver biopsies retrieved hepatic tissue, and 22% of the samples were less than 2 mm long and lacked appropriate lobular architecture.7 Thirteen percent of the samples were completely devoid of tissue, and another 10% contained skeletal muscle, blood, or small intestine. Only 60% of samples obtained by Tru-Cut biopsy were of diagnostic quality.7
In another study, samples obtained with 18-ga spring-triggered biopsy needles using ultrasound guidance or direct observation during laparotomy or immediately postmortem had one-third to one-fourth of the median surface area of those obtained with wedge biopsy.8 Because of this small sample size, a diagnosis based on needle biopsy correlated with that of wedge biopsy in less than half the patients. Additionally, the severity of pathology was graded as significantly less in needle biopsy samples for most morphologic parameters, with the exception of inflammation, which was graded more severe as compared with wedge samples. Smaller needle biopsy samples were unable to achieve the necessary number of portal triads per sample to provide an accurate diagnosis of portal triad diseases such as portal venous hypoplasia or portal atresia and were subject to misinterpretation by evaluators.8 Laparoscopic biopsy allows better visualization of the site compared with ultrasonography but may provide less tissue volume compared with a surgical wedge biopsy.
All patients should undergo presurgical diagnostic tests (complete blood count, platelet count, serum chemistry profile, coagulation tests, urinalysis) to determine which perioperative treatments should be administered. For example, animals with liver disease may present with vomiting that could result in dehydration and electrolyte abnormalities. Preoperative potassium or magnesium deficiencies may cause ileus, arrhythmias, and other complications during or after surgery, so they are best corrected before anesthesia. Animals with severe liver disease or sepsis may have prolonged clotting times, requiring crossmatching and transfusion before surgery.2,3 Animals suspected of having neoplasia should undergo staging of their disease, including thoracic radiography and abdominal ultrasonography. Aspirates obtained during ultrasonography may provide a diagnosis in some patients, obviating the need for surgery.
If possible, fast patients for 12 hours before surgery. Preoperatively, administer fluids and analgesics. Give hypoalbuminemic patients colloidal fluids such as hetastarch or plasma to provide oncotic pressure support. Choose premedicants and dosages with care since metabolism of some drugs may be delayed when liver dysfunction is present. We commonly use an opiate combined with a benzodiazepine in dogs and cats or a combination of ketamine and diazepam in cats. If acepromazine is administered as a sedative, the total dose should not exceed 0.25 mg. Induction can be performed with intravenous propofol or by mask induction with isoflurane. Clip patients undergoing liver biopsy to the midsternal level, and clip patients receiving feeding tubes farther laterally on the abdomen. All patients should have an appropriately sized endotracheal tube with an inflated cuff. During anesthesia, continuous-rate infusions of fentanyl can be administered to reduce gas anesthetic requirements.9,10 These infusions can be continued postoperatively to provide analgesia.
Ideally, respiratory and cardiac function and oxygenation should be monitored during anesthesia with a capnograph, electrocardiograph, arterial blood pressure monitor, and pulse oximeter. Maintaining intraoperative blood pressure with fluids and oncotic support is critical in patients with liver disease since reduced hepatic perfusion can have deleterious effects on postoperative liver function. Forced-air heating blankets (e.g. Bair Hugger—Arizant Healthcare) can be used to keep patients warm during the procedure.
Prophylactic antibiotics are usually unnecessary in patients undergoing liver biopsy. Be prepared to take culture samples during the procedure and to place feeding tubes in some patients. Cautery should be available intraoperatively for patients with coagulopathies. Count the sponges and laparotomy pads before the abdomen is opened and again before it is closed to prevent iatrogenic peritoneal foreign bodies. Suction all fluid from the abdominal cavity before closure.
Postoperative treatments, complications, and prognosis vary depending on the underlying disease process and the patient's condition. Most animals continue to receive fluid support and analgesics after surgery. In patients that are not vomiting, small amounts of food and water can be offered within eight hours of the procedure.
OPEN SURGICAL BIOPSY TECHNIQUE
Make a ventral midline abdominal incision. The incision should extend cranially to the level of the xiphoid to improve exposure of the liver, particularly if it is small. Liver exposure can be improved by removing the falciform fat and by carefully incising the triangular ligaments or by placing moistened laparotomy pads between the liver and the diaphragm.2,3 Examine the entire liver visually and by gentle palpation for nodules, cavitations, and other abnormalities.
Peripheral or diffuse lesions
When taking biopsy samples of the liver with clamshell forceps, place the instrument against the site of interest with the jaws open. Insert the forceps into the parenchyma to the level of the angle of the jaws, and close the jaws. After a few seconds of crushing, twist the instrument until a free piece of tissue is removed. Pulling the forceps straight out of the liver tends to cause more hemorrhage than twisting.12
Hemorrhage from punch, Tru-Cut, or clamshell biopsy sites can be controlled by a variety of methods. Absorbable gelatin foam (Gelfoam—Pharmacia & Upjohn) can be inserted into the defect, a mattress suture of 3-0 absorbable material can be placed gently around the defect, or an omental flap can be sutured over the defect. Alternatively, pressure can be applied to the site, or the site can be cauterized by using a low setting.4,13 Thoroughly lavage the abdomen with a balanced electrolyte solution in patients with bile leakage, excessive hemorrhage, or infected or necrotic lesions.2
Complications after liver biopsy are uncommon but may include bile peritonitis, hemorrhage, and sepsis. The risk of complications is greater in patients with coagulopathies and thrombocytopenia.14,15 Major complication rates during hepatic biopsies have been reported to be as high as 22% and 50% in dogs and cats that are thrombocytopenic.14 Many patients with liver disease are debilitated from hypoalbuminemia and compromised liver function, increasing the risk of potential complications with anesthesia and surgery such as hypotension and altered metabolism of anesthetic and analgesic drugs.
Diana Burger, BS
Amie Carrier, BS
Karen M. Tobias, DVM, MS, DACVS
Department of Small Animal Clinical Sciences
College of Veterinary Medicine
The University of Tennessee
Knoxville, TN 37996-4544
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13. Kim EH, Kopecky KK, Cummings OW, et al. Electrocautery of the tract after needle biopsy of the liver to reduce blood loss. Invest Radiol 1993;28:228-230.
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15. Weber JC, Navarra G, Jiao LR, et al. New technique for liver resection using heat coagulative necrosis. Ann Surg 2002;236:560-563.