Gastrointestinal (GI) biopsies are indicated to help diagnose inflammatory bowel disease (IBD) and to rule in or out GI neoplasia. Biopsies of the gut can be performed endoscopically (from either or both ends!) or at laparotomy or laparoscopy. Pancreatic biopsies can also be very helpful but can only be performed at laparotomy or laparoscopy.

The right time to perform biopsies varies with the patient and indication. The right method of performing biopsies requires a careful risk-benefit analysis in every patient, considering also the potential value of the biopsy specimens, i.e., always ask yourself: 'will a biopsy change treatment?' GI biopsies are invasive. Laparotomy is more invasive than endoscopic biopsies. Fine-needle aspiration (FNA) is the least invasive of all. However, the diagnostic value of biopsy specimens is almost inversely proportional to the degree of invasiveness: FNAs can be very misleading; endoscopic biopsy specimens are only partial thickness and the diagnostic yield depends on operator experience. Worryingly, it has been shown that the diagnosis obtained with endoscopic biopsies can vary between pathology laboratories: even between lymphoma or normal with the same biopsy specimen. Publication of the new WSAVA guidelines on GI pathology should increase interoperator agreement on pathology. Full-thickness biopsy specimens taken from stomach, a variety of small intestinal sites and pancreas (and often also liver and mesenteric lymph nodes) undoubtedly give the best diagnostic yield but there is greater morbidity with this approach - and some patients may even die post biopsy. One study showed full-thickness surgical biopsy did not change treatment recommendations; if this is the case, the benefits definitely do not outweigh the risks of full-thickness GI biopsies in many patients.

If clinical and imaging findings give a strong suspicion of neoplasia, then biopsies should be considered as early as possible. Diffuse GI lymphoma can be diagnosed in some cases with FNA cytology of the gut wall and intestinal lymph nodes under ultrasound guidance. This is the least invasive option, but the clinician and cytologist should look for confirmation of neoplasia in several sites before being convinced of the diagnosis. Endoscopic biopsies may give a diagnosis, although many carcinomas are submucosal and may not be accessible by endoscopy. In addition, access is limited: endoscopy will only reach as far as the proximal duodenum from the front end or as far as the distal ileum from the back end - leaving a large portion of the small intestine inaccessible. Various forms of 'push' and 'capsule' endoscopy in humans manage to cover most of the small intestine but these are not yet in clinical use in small animals. Full-thickness biopsy specimens are best but there is a very significant risk of gut wall dehiscence if the gut wall is neoplastic. Severe hypoproteinaemia, which is also common in GI tumours, may also reduce healing. Before proceeding to perform biopsies in a case of potential neoplasia, the question again has to be asked: will this change treatment? If surgical excision of a mass is an option, then clearly it will. If GI lymphoma is suspected, then perhaps it will not. In dogs, the prognosis with GI lymphoma is very poor even with chemotherapy. Treatment with prednisolone without biopsy is an option in cases where the differentials are IBD or lymphoma. A recent study suggested dogs with IBD did better with a combination of prednisolone and chlorambucil than with prednisolone treatment alone, so this again would be a logical option in cases which did not have a biopsy.

In cases with suspected IBD, the right time to biopsy is not on the first visit. As detailed in the WSAVA guidelines, IBD is by definition an 'idiopathic' inflammation of the gut wall. GI inflammation will also be seen secondary to parasites and bacterial and viral infections in the gut and food allergies. These should be ruled out first before intestinal biopsies are performed; if they are not, interpretation of any histological changes in the gut wall is impossible. IBD is not purely a histological diagnosis - a histologist can support the diagnosis but the clinician has to rule out other causes first. In addition, in several studies, histological severity did not correlate to disease severity and also histological changes did not resolve when clinical signs resolved - so repeat biopsy is not indicated to demonstrate disease resolution. Monitoring clinical signs is more fruitful to demonstrate response to therapy. Biopsies can be performed after faecal samples have ruled out obvious pathogens and a diet trial has ruled out food allergy. A 4-week course of antibiotics (metronidazole or tylosin) to rule out antibiotic-responsive diarrhoea is also wise before considering biopsies. The WSAVA recommend endoscopic biopsies rather than full-thickness biopsies because the former have lower morbidity. However, remember that endoscopic biopsies have limitations related both to operator skill and limited access: if the IBD is most severe in the jejunum, this will be missed. Remember also to discuss all the risks and benefits with the client: it may be preferable in some cases simply to start steroid treatment after the diet and antibiotic trials and assess response to treatment rather than perform a biopsy: ask yourself: 'will this biopsy change my treatment decisions?'

References

1.  Day MJ, Bilzer T, et al. Histopathological standards for the diagnosis of gastrointestinal inflammation in endoscopic biopsy samples from the dog and cat: a report from the World Small Animal Veterinary Association Gastrointestinal Standardization Group. Journal of Comparative Pathology 2008;138(Suppl 1):S1–43.

2.  Shales CJ, Warren J, et al. Complications following full-thickness small intestinal biopsy in 66 dogs: a retrospective study. Journal of Small Animal Practice 2005;46:317–321.

3.  Willard MD, Jergens AE, et al. Interobserver variation among histopathologic evaluations of intestinal tissues from dogs and cats. Journal of the American Veterinary Medical Association 2002;220:1177–1182.

4.  Willard M, Mansell J. Correlating clinical activity and histopathologic assessment of gastrointestinal lesion severity: current challenges. Veterinary Clinics of North America Small Animal Practice 2011;41:457–463.