Definitive diagnosis of disease involving the parenchymal abdominal viscera often requires a representative specimen of affected tissue. Methods used to obtain tissue samples range from those that are minimally invasive, such as fine-needle aspiration (FNA), to more invasive techniques such as surgical biopsy. FNA and cytological examination can be a useful diagnostic tool and is commonly used for hepatic, splenic and lymph node specimens. FNA is an easy and cheap procedure that is best suited to diffuse disease and can be performed at low risk to the patient. However, its accuracy and agreement with the histopathological findings vary depending on the underlying disease and it often fails to provide information on parenchymal architecture. Importantly, FNA for cytological examination of the liver has serious limitations when used to identify the primary disease process due to the small sample size obtained.
Despite introduction of techniques such as CT, and MRI scan, biopsy is still considered a "golden standard" to obtain a definitive diagnosis. This review provides practical guidance on the open surgical approach to obtain gastro-intestinal, hepatic, pancreatic, and splenic specimens in veterinary patients. The information presented is based on peer-reviewed publications and the clinical experience of the author.
BIOPSY OF THE GASTRO-INTESTINAL TRACT
The standard approach for open surgical biopsy of the abdominal organs is a ventral midline laparotomy. The edges of the surgical incision should be protected with saline-soaked laparotomy pads and the organ to sample exteriorized and isolated from the remaining abdominal contents.
SUTURE MATERIAL FOR GASTRO-INTESTINAL CLOSURE
Although most absorbable suture materials can be used, monofilament synthetic suture like poliglecaprone-25 (Monocryl™, Ethicon) 3-0 for the stomach and 4-0 for the intestine is preferred. Long-lasting monofilament, absorbable, suture such as polydioxanone (PDS) or polygliconate (Maxon) or nonabsorbable suture like nylon or polypropylene should be selected for patients with prolonged tissue healing. For hand-sewn intestinal closure, either continuous or interrupted patterns can be used with equal efficacy. The absorption data of poliglecaprone 25 show that at 7 days it retains 50–60% of its strength, at 14 days it retains 20–30% and at day 21 it has lost all tensile strength. This makes it ideal for gastric and small intestinal surgery where prolonged wound support is not required.
In order to avoid compromising gastro-intestinal blood supply and to reduce leakage and bacterial contamination of the peritoneal cavity with intestinal content, meticulous and gentle surgical technique is very important.
STOMACH
Full thickness gastric biopsy is indicated in the presence of submucosal, parietal disease when endoscopic biopsy is inadequate (Fig. 1). Because of its anatomical localization, the stomach cannot be entirely exteriorized. In order to minimize spillage of gastric content, pre-placement of stay suture permitting elevation of the area to be sampled is therefore recommended (Fig. 1a).
When diffuse gastric disease is suspected, a rectangular or elliptical full thickness sample of the gastric wall (including mucosal, submucosal, muscularis and serosal layers) is usually collected from the body of the stomach Fig. 1b and c). Contrarily, focal lesions require selective sampling.
Gastrotomy incisions are usually closed with a two-layer inverting pattern suture (Cushing pattern). The first layer can also be a simple continuous appositional pattern and usually incorporates the gastric mucosa. The second layer instead should incorporate the serosal and mucularis layers of the gastric wall (Fig. 1d).
INTESTINE
Surgical exploration of the intestine should be careful and should begin with palpation of the duodenum. The entire length of the intestine should be explored because multiple lesions may be present. The affected intestinal segment is then exteriorised and isolated from the rest of the abdominal organs with saline-soaked swabs (Fig. 2). Intestinal content is milked orally and aborally and kept apart from the surgical site by occluding the intestinal lumen with Doyen forceps or with the help of the assistant's finger (Fig. 2a).
An elliptical or rectangular incision with a number 11-scalpel blade in the antimesenteric border of the affected intestinal segment is made (Fig. 2b).
Biopsying the intestine with a wedge incision is not recommended since it would carry the risk of collecting little or no mucosa, and the pathologist would therefore not be able to give a meaningful interpretation. In the author's experience, excision of a longitudinal rectangular wall portion (0.5–1 cm × 0.3–0.5 cm) provides a good sample for interpretation (Fig.s 2c). Prior to closure of the wall defect any mucosa protruding from the wound should be trimmed with fine Metzenbaum scissors. The antimesenteric rectangular defect is then closed longitudinally with simple interrupted pattern of 4-0 monofilament absorbable suture such as poliglecaprone 25 (Fig. 2d).
An alternative for intestinal biopsy is to use a 4 or 6 mm skin punch biopsy instrument, which is ‘pushed’ through from the serosa to the lumen. The resulting defect is closed, either longitudinally or transversely (depending on the width of the intestine), with simple interrupted 4-0 sutures.
The suture line can then be reinforced with omentopexy. This consists in placing a portion of omentum over the intestinal incision and around the affected intestinal loop.
When an obvious intestinal lesion cannot be detected, multiple samples, from the duodenum, jejunum and ileum, should be taken (Fig. 3).
BIOPSY OF THE LIVER
Liver biopsy is an important step in the evaluation of animals with hepatic disease. It permits formulation of a diagnosis and treatment plan, and an accurate prognosis. However, a single liver specimen evaluates only a small portion of hepatic tissue and may not represent the entire liver. Therefore, when possible, samples from multiple lobes are preferred, even when the parenchyma appears uniform. In preparation for biopsy it is important to assess the patient’s coagulation status. Where there is diffuse hepatic disease, any part of the liver can be sampled. Focal lesions require selective sampling under ultrasound guidance or direct visualisation via a laparoscopic or surgical approach. Large lesions should always be sampled in the periphery because the centre may be necrotic.
OPEN SURGICAL LIVER BIOPSY
If patients are having surgical procedures performed on the hepatobiliary tract, open surgical hepatic biopsies are obtained. It is recommended that a surgical liver biopsy is taken early during the laparotomy because hepatocellular damage can result from prolonged anaesthesia, vascular changes and manipulation of the bowel. The advantages of surgery are the exposure, direct visualisation, and ability to manipulate and palpate the tissues and monitor the biopsy site for bleeding. There are several techniques for obtaining open surgical liver tissue, including suture fracture and punch biopsy.
Suture fracture technique
For diffuse liver disease, the easiest procedure to perform is the suture fracture (or guillotine) technique on the periphery of the liver lobes (Fig. 4). These areas are easily accessible and the vascular and biliary structures are small. The tip of an accessible liver lobe is selected and exteriorized (Fig. 4a) An encircling loop of 4-0 monofilament absorbable suture material is placed around the hepatic tissue to be sampled and tightened (Fig. 4b), crushing the hepatic parenchyma and occluding associated ducts and vessels (Fig. 4c). The hepatic specimen distal to the ligature is excised with a scalpel blade (Fig. 4d). Any bleeding is identified and addressed.
Punch biopsy
A hepatic lesion that is located away from the periphery of the liver lobe can be biopsied using the punch biopsy technique (Fig. 5). Generally a 4–6 mm punch is used (Fig. 5a). The biopsy punch is inserted into the liver parenchyma at the desired side and rotated back and forth over the lesion until sufficient depth has obtained (Fig. 5b). Insertion depth should be limited to less than half the thickness of the lobe to avoid damage to larger hepatic vein branches. The punch is angled across its base to sever any deep attachments and the hepatic specimen is removed (Fig. 6a & b). A plug of haemostatic collagen sponge is finally inserted into the resulting defect to limit blood loss (Fig. 6c & d).
BIOPSY OF THE PANCREAS
In contrast to pancreatitis in dogs, feline pancreatitis can be a very difficult disease to diagnose. In general, a definitive diagnosis of feline pancreatic disease requires a combination of clinical suspicion, changes on abdominal ultrasonography and histological examination of biopsies. The most reliable method for making an accurate diagnosis of pancreatic disease remains direct visualisation and histopathology.
OPEN SURGICAL PANCREATIC BIOPSY
Diffuse pancreatic disease
In animals with diffuse pancreatic disease, biopsy is generally performed at the distal aspect of the right limb of the pancreas due to its distance from the pancreatic duct system and major blood vessels. Pancreatic biopsy may be performed using a scalpel blade to obtain a wedge biopsy specimen, punch biopsy tools to obtain a cylindrical specimen, or via a suture fracture technique (Fig. 7)
The wedge biopsy sample is collected by perforating the mesoduodenum close to its pancreatic insertion and isolating a triangular section of the pancreas (approximately 5 x 5 x 7.5 mm) with two curved clamps. The biopsy is dissected along the clamps with a scalpel and a 4–0 monofilament absorbable ligature is placed behind the clamps. This suture decreases leakage of pancreatic enzymes but may lead to some local adhesion formation.
Suture fracture biopsy is performed by passing the suture around the pancreatic tissue segment to be removed (Fig. 7a & b). The suture is then tightened, crushing the pancreatic parenchyma and occluding associated ducts and vessels (Fig. 7c). Pancreatic tissue distal to the ligature is excised and the mesoduodenum is closed (Fig. 7d).
Localised pancreatic disease
Biopsy of single or multiple localised pancreatic lesions can be excisional (partial pancreatectomy) using the suture fracture technique or wedge biopsy if positioned in the left or right pancreatic limb.
In cases in which the lesion is localised within the body of the pancreas, partial pancreatectomy cannot be performed and the biopsy may need to be collected with a core biopsy needle or a punch biopsy instrument. However, occlusion of associated ducts and vessels cannot be achieved and there may be postoperative pancreatic enzyme leakage. A blunt dissection and ligature technique could alternatively be used. Using this method, pancreatic tissue to be removed is isolated from the remaining pancreas by blunt dissection with a Halsted mosquito hemostat or sterile cotton swabs. Associated vessels and ducts are ligated or cauterised, the pancreatic tissue is excised and the mesoduodenum is closed. Care must be taken to avoid damage to the duct system and to the major vascular supply to the area. In particular, it is very important to avoid injury to the pancreaticoduodenal vessels to prevent duodenal necrosis.
BIOPSY OF THE SPLEEN
There is limited information in the veterinary literature regarding biopsy of the spleen. Splenic biopsy alone is rarely an indication for laparotomy. This may be due to the nature of splenic disease in companion animals, which often necessitates splenectomy rather than biopsy, as well as a perceived fear of complications associated with biopsy of such a highly vascular organ.
OPEN SURGICAL SPLENIC BIOPSY
For diffuse splenic disease, the easiest procedure to perform is the open surgical suture fracture technique on the periphery of the splenic tail (Fig. 8). The tip of the tail is easily accessible and haemorrhage is rare after tissue specimen collection. For single or multiple lesions located away from the periphery of the spleen, partial or complete splenectomy may be the technique of choice.
