Liver biopsies are an underused technique in the veterinary field. Indications for a liver biopsy include suspected diffuse hepatic disease, masses, icterus, ascites, etc. Biopsies are important in obtaining a definite diagnosis and formulating a successful treatment plan. Depending on the patient’s overall health, symptoms, and tentative diagnosis, some biopsy techniques may be better suited than others. Let’s review the different techniques for liver biopsies and where they can be most useful.
Ultrasound-guided biopsies are a good option for patients who are poor anesthetic or surgical candidates, such as pets with severe coagulopathies. With the advent of ultrasonography, blind percutaneous sampling should be avoided because of the risks involved in performing it.
Ultrasound-guided biopsies allow samples to be taken from a specific lesion, helping to avoid large vessels and biliary ducts. However, there are a few downsides to this technique. Certain patient factors, such as large-volume ascites, micro-hepatica, and liver cysts or abscesses, make ultrasound-guided biopsies less optimal or even contraindicated. Another issue with this technique is sample size and fragility. Trucut biopsies tend to only contain portions of liver lobules, which can be fragmented and difficult to read by a pathologist. The smaller the biopsy, the less likely it is that portal areas and hepatic architecture can be evaluated.
According to Jim Walberg, DVM, Dipl. ACVP, a board-certified pathologist at VetPath Services in Stone Ridge, N.Y., Trucut biopsies are inferior to surgical biopsies, offering approximately 60 percent accuracy.
Although some ultrasonographers routinely perform fine needle aspirates, Dr. Walberg offers a different perspective. “Fine needle aspirates are the least accurate option and often do not correlate with wedge biopsies,” he explains. “They are most useful for diffuse disease, such as hepatic lipidosis and lymphosarcoma.”
Laparoscopy is another minimally invasive technique for obtaining liver biopsies. It allows for good visualization of the liver (and other abdominal organs) without a laparotomy, especially in patients in which open surgery or lengthy anesthesia is risky or contraindicated.
It is a useful technique to determine mass size and whether resection is possible. Laparoscopic biopsies require general anesthesia. Trocars are positioned strategically to access the abdomen with the camera and sampling instruments.
Patients with ascites (in which ultrasound may not be as effective) can successfully have a laparoscopic liver biopsy taken with minimal to no leakage if trocar sites are sutured meticulously. The procedure does not require removal of the ascites fluid, which can help reduce protein loss.
Multiple samples can be harvested depending on the findings. Laparoscopic biopsies provide an adequate representation of the liver, and hemorrhage is not a common complication. Bleeding can be easily visualized and inspected following sample retrieval. Responses to hemorrhage include the application of pressure and gelatin sponge insertion at the sampling site.
Liver biopsy via laparotomy is considered the gold standard by many. It not only allows for optimal sampling, but also visualization and palpation of the entire liver, in addition to all other abdominal organs. It is also useful for determining the size of the liver and to assess nodules or other lesions.
It may be difficult to justify a laparotomy for the sole purpose of harvesting a liver biopsy, unless it’s the only practical option in your practice. However, liver biopsies are commonly performed during a laparotomy done for other reasons.
Liver exposure can be greatly improved by removing the fat-laden falciform ligament and then placing a Balfour retractor. There are several ways to perform an incisional liver biopsy during a laparotomy, including the guillotine method, Trucut needle, and punch biopsy. Let’s look at each:
1) The guillotine, a.k.a. wedge biopsy or suture-fracture technique, is commonly used when you need to sample a pointed or sharp-edged liver lobe. Create a loop by placing a simple knot in appropriately sized suture material (usually polydioxanone) and slide it around the edge of a liver lobe. Settle the suture into natural landmarks (e.g. liver fissures) or small notches made with hemostats. Tighten the suture, crushing the tissue within the loop and ensuring hemostasis.
Be careful not to pull up or out on the suture material when tightening, as this may remove the ligature from the liver and lead to hemorrhage. Alternatively, you can first place a curved hemostat or right-angle forceps around the area to sample, then place your ligature behind it.
Cut the sample 2 to 3 mm from the ligature with a scalpel blade or Metzenbaum scissors. Be careful not to handle the sample with tissue forceps or hemostats, as this could cause iatrogenic trauma and specimen artifact. Instead, use your fingers or a piece of sterile paper (hint: from a pack of suture) to collect the fragile sample. Trim the ligature ends short and stop any bleeding by applying pressure or an additional ligature. Sterile hemostatic power can be applied if necessary.
If generalized disease is suspected, then at least two wedge biopsies are recommended from different lobes. A similar technique can be adapted for excisional liver biopsies, although a double ligature may be wise.
2) Even though they are not as accurate as a wedge biopsy, Trucut biopsy needles can be helpful to obtain samples that aren’t on the outer edges of the parenchyma. They can sample deep tissue lesions without being too invasive or traumatic, or resect a huge portion of a liver lobe.
3) The other technique that can be used for sampling the liver is a skin biopsy punch. This allows taking multiple samples from any location throughout the liver, not only on the edges. Punches range in diameter (1 to 10 mm) depending on the sample size you need to obtain. After thorough examination of the liver, determine the location and number of samples required. Choose your punch size and pick a biopsy site.
Be sure not to exceed half of the lobe’s thickness. Any bleeding can be controlled quickly by inserting a piece of gelatin sponge into the excision site.
After bleeding has been controlled, lavage the abdomen if needed before standard closure. Be sure to place your samples in a large amount of formalin. The ideal ratio is 10 to 20 times more formalin than tissue. Always provide a thorough and relevant history to your pathologist. Simply writing “liver biopsy” on the request form is less than ideal and clearly not very helpful.
If you follow recommended guidelines, no technique discussed here produces significantly more bleeding than the other. The biggest difference and deciding factors are patient conditions, suspected diagnosis, and required sample size. More diffuse disease can be biopsied with a Trucut biopsy needle or ultrasound-guided biopsy, especially in patients for which surgery is not a great option. Small or damaged biopsies can lead to misdiagnosis or under-diagnosis of liver disorders. Ultimately, the larger the biopsy, the more likely it is that portal areas and hepatic architecture can be evaluated, and the more accurate the diagnosis will be.
Phil Zeltzman, DVM, DACVS, CVJ, Fear Free Certified, is a board-certified veterinary surgeon and author whose traveling surgery practice takes him all over Eastern Pennsylvania and Western New Jersey. You can visit his website at www.DrPhilZeltzman.com. He also is cofounder of Veterinary Financial Summit, an online community and conference dedicated to personal and practice finance (www.vetfinancialsummit.com). Kat Christman, a certified veterinary technician in Effort, Pa., contributed to this article.