Biopsies should only be performed for a clear purpose, such as for the differential diagnosis of benign tumors or to analyze the stage and grade of malignant tumors, which would allow the area to be resected to be determined. Depending on the purpose of a biopsy and the lesion characteristics, the surgeon can choose from a range of different biopsy techniques, including punch, incisional, and excisional biopsies. In the case of incisional biopsies, normal skin should be excised together with early-stage lesions and the characteristic areas of lesions (e.g., inflammatory, erosive, or ulcerated areas).

The aim of staging systems is to quantify the disease and to offer a more accurate treatment and prognosis. Staging should define the site/origin and extent of the primary tumour, the sites of metastases (local and distant) and histological type. Many systems will also grade the tumours histologically, especially mast cell tumours. It is essential when considering biopsy of any mass to assess draining lymph nodes and biopsy them as necessary. Checks for distant metastases should also be performed, be it thoracic radiography and or abdominal ultrasound.

(Below is the TNM classification for canine oropharyngeal tumours.)

TNM staging

Clinical stage TNM

Biopsy Techniques

The biopsy technique chosen will depend on location and size of the mass and ultimately the personal preference of the surgeon. The aim of biopsy is to collect as many cells as possible in order that a diagnosis is obtained but without compromising any further definitive surgery that the patient may require. It is also essential when taking a biopsy that the procedure does not spread the disease process to adjacent tissues. It is common for the biopsy site to be at the margin of what appears to be normal and abnormal tissue; when this is done, it is important that any scar tissue can be included in definitive removal.

The common biopsy techniques are

 Needle core biopsy

 Punch biopsy

 Incisional biopsy

 (Excisional biopsy)

Needle Core Biopsy

This is a useful technique for both cutaneous and deeper masses and has the particular advantage that it can be used with ultrasound guidance to obtain biopsies of parenchymal organs such as the liver or kidney. For most purposes, a spring loaded or air driven automated needle is ideal; it helps to reduce operator error when sampling. A number of papers have shown that larger gauge needles (e.g., 14 gauge) will provide a better yield and are more likely to be diagnostic than narrow gauge (e.g., 18 gauge). Poor cell yield is the major disadvantage of this technique.

The needle itself has an inner obturator with a biopsy notch and an outer cannula with a cutting rim.

The closed instrument is inserted into the tissue and the outer cannula is then slid backwards (either manually or via the spring loading mechanism); this allows the tissue to enter the biopsy. Firing the instrument pushes the outer cannula forward and cuts the surrounding tissue, 'trapping' the sample in the biopsy notch. Following removal of the instrument, any haemorrhage is dealt with by applying pressure to the tract. A 25-gauge intravenous needle can be used to roll the sample from the notch into formalin or a biopsy cassette.

Punch Biopsy

Punch biopsies are ideal for superficial lesions and come in a variety of sizes, from 3 mm diameter upwards. In most cases, a 4 or 6 mm diameter biopsy is preferred.

A sterile punch is rotated clockwise and then anticlockwise to the required depth and then removed. Fine forceps are used to raise the sample from its 'bed' and the deep tissue excised using either fine Metzenbaum scissors or a number 11 scalpel blade. The resulting skin defect is sutured with an appropriate size of monofilament nylon in a cruciate mattress or simple interrupted pattern.

Incisional Biopsy

This is the 'classic' technique of taking a slice of tissue from both the lesion and normal surrounding tissue using a scalpel. It has the advantage that larger samples can be taken and is particularly useful where there are areas of infected or necrotic tissue within a lesion. The incision should only be large enough to obtain an adequate sample and is always planned to ensure that the resulting wound can be excised when definitive surgery is carried out. It is also essential that when including normal tissue that the extent of dissemination of any diseased cells is kept to a minimum. Wound closure is routine and is closed from deep to superficial layers

Excisional Biopsy

This technique involves removing the mass together with a narrow band of normal tissue. It can only be recommended where there is ample tissue to allow for a more radical surgery should the mass prove to be invasive. Allowance needs to be made for deep as well as lateral margins in such a case. Excisional biopsies also run a greater risk of seroma development, which can aid seed diseased cells along fascial planes, making definitive surgery even more radical.

Specific Biopsy Techniques

A. Hepatic Biopsies

Prebiopsy Considerations

Severe haemorrhage is a potential consequence of hepatic biopsy in small animals, but it is rare; it is only likely if there is as significantly prolonged bleeding time or a concurrent thrombocytopenia (usually when the patient has a disseminated intravascular coagulopathy [DIC]). In animals with severe hepatocellular damage, or a suspected complete extrahepatic bile duct obstruction, a coagulation profile should be obtained preoperatively. It is now recognised that in patients with only mild coagulation abnormalities, postoperative haemorrhage is rare.

Percutaneous Ultrasound Guided Liver Biopsy

The competent ultrasonographer can identify focal hepatic lesions such as neoplasia, cysts or abscesses; or identify generalised changes in the hepatic parenchyma. This can allow for accurate guided needle or core biopsies to be taken from solid lesions. The advent of 'one-handed' biopsy instruments has made this easier. Cysts and abscesses should not be biopsied percutaneously.

Surgical Biopsy

This has the advantage of allowing exploration of the abdomen, and specific areas of the liver can be biopsied. The disadvantage is that a general anaesthetic and an invasive surgical procedure is required. It is important to consider the role of the liver in metabolising sedative and induction agents in particular when choosing an anaesthetic protocol.

Bleeding from the biopsy site can be identified and controlled. If generalized, hepatic disease is present, the biopsy can be taken from the most accessible site. With focal disease, the entire liver should be palpated carefully for the presence of intraparenchymal nodules or cavities.

Guillotine Technique

Marginal biopsy samples using ligatures are easy to obtain. A loop of a synthetic absorbable ligature is passed over an easily accessible edge of liver lobe and the parenchyma crushed as the ligature is tightened, thereby ligating vessels and biliary ducts. The sample is removed by amputating approximately 5 mm distal to the ligature. If there is any haemorrhage, an absorbable haemostatic material can be applied or the omentum is placed over the site.

Forceps Technique

A pair of haemostatic forceps is placed across the tip of a liver lobe to crush the parenchyma. Tissue distal to the forceps is excised with a scalpel. Absorbable mattress sutures may be placed proximal to the forceps if required to control haemorrhage.

'Forceps' technique for liver biopsy

'Punch' Biopsy

Since the forceps technique is relatively straight forward a 'punch' technique is rarely required. It is use is generally limited to focal lesions on the ventral liver surface and care must be taken not to penetrate deeper than 50% of the parenchyma. The resulting defect can either be sutured with a mattress suture of a synthetic absorbable suture material, or plugged with omentum or an absorbable haemostatic material.

Laparoscopy

This technique allows visualisation of the liver and for focal biopsy with a minimally invasive technique. The disadvantage currently is expense of the equipment and that few surgeons have the necessary experience in its use.

B. Pancreatic Biopsy

If pancreatic biopsy is to be carried out, the surgeon must know the location of the pancreatic ducts and understand the blood supply to the pancreas.

Anatomical relationship of pancreatic ducts

Blood supply to the pancreas

It is essential that neither the duct system nor the vascular system is damaged as part of the biopsy procedure.

In cases where there is diffuse disease, the tip of the right (duodenal) limb is chosen, due to its accessibility; and given its peripheral position, the risk to ducts and vessels is small. Either a suture fracture or surgical dissection and ligation can be used. Whichever technique is used, it is essential to suture the mesoduodenum closed and to cover the wound with omentum. This will help minimise the risk of pancreatic enzyme leakage.

Since pancreatitis may occur as a result of surgical biopsy, it is wise to starve patients for 24–48 hours postoperatively to reduce exocrine pancreatic secretion.