Feline gastrointestinal (GI) endoscopy is in high demand, particularly by cat owners already aware of the clinical benefits and availability of this procedure within the human health care system. This lecture will provide a basic introduction to GI flexible endoscopy including important aspects of endoscope selection, clinical indications, and basic techniques required to perform a thorough and diagnostically meaningful examination in the cat.

Introduction

Gastrointestinal endoscopy offers a minimally invasive method for obtaining a relatively thorough examination of the GI. Procurement of biopsy samples is often necessary in achieving a diagnosis in patients presenting with chronic or recurrent gastrointestinal tract signs (>2 weeks). In addition, endoscopy also offers a minimally invasive option for foreign body retrieval, oesophageal stricture dilation therapy and percutaneous gastrostomy tube placement.

Endoscopy should be considered the next logical step when investigating those patients where haematology, biochemistry, electrolytes, anthelmintic therapy, B12 assessment/supplementation, fPLI/TLI, and abdominal imaging have failed to provide an explanation for presenting clinical signs. In cats, oesophagoscopy, gastroduodenoscopy, proximal jejunoscopy, distal jejunoscopy, ileoscopy and colonoscopy should always be considered in those cases presenting chronic weight loss, polyphagia, hyporexia/anorexia or chronic hypocobalaminemia. This is especially true for cases with confirmed hypocobalaminemia where significant distal small intestinal evaluation/biopsies are required. The World Small Animal Veterinary Association (WSAVA) International GI Standardisation Group and the American College of Veterinary Internal Medicine (ACVIM) have published multiple statements to provide guidance and standards for performance and interpretation of various diagnostic tests in dogs and cats presenting with gastrointestinal signs, including treatment trials, patient response, and outcome.^1,2 Interestingly, inflammatory bowel disease (IBD) and lymphosarcoma (LSA) are often the remaining differential diagnoses in these patients. The clinical history and findings up to this critical point seems to present a clinical conundrum for the practitioner resulting in either polypharmacy or offering invasive interventions (e.g., exploratory laparotomy). It’s not unsurprisingly that both of these options are often met with resistance by both patient and cat owners.

For most practitioners, the most challenging question associated with obtaining biopsies is how to obtain tissue samples of adequate depth and at the correct anatomic location. Whether to obtain full thickness biopsies or endoscopic biopsy samples has been a subject of discussion over the past 10–15 years. Benefits of endoscopic biopsies include the ability to directly visualise and document mucosal changes and lesions, enabling direct access and biopsies of these changes, to collect multiple tissue samples from each anatomic site, and to begin anti-inflammatory or chemotherapy without delay after the procedure.³ Unfortunately, endoscopy has some limitations in that it rarely diagnoses functional diseases (e.g., dysmotility, dietary hypersensitivity, antibiotic-responsive disease, etc.), lesions outside the GI tract (liver, pancreas, etc.) nor allows for full evaluation of the entire jejunum.³ Other clinical challenges associated with implementing endoscopy into a GIT investigation include lack of appropriate/suitably-sized equipment to perform a thorough examination, insufficient operator training/understanding how to ‘drive the ‘scope’ through the gastrointestinal tract, and/or confidence with identifying normal from abnormal. The endoscopist performing procedure should also have a high level of proficiency, as GI endoscopy in cats is more demanding in skill than in dogs, due to the small size of the animal and the decreased tolerance to anaesthesia.

Theoretical risks which should be communicated with the owner include:

1.  General anaesthesia

2.  Bowel perforation

3.  Bleeding

4.  Non-diagnostic samples (depth of sample and length of endoscope in relation to lesion).

Saying that, these risks are considered rare.

Equipment

A flexible endoscope suitable for performing an upper and lower GI examination in cats should be no greater than 8.0 mm in diameter, at least 100 cm in length and must have four-way tip deflection. In Oriental lines, where the antral canal, pylorus and ileocolic sphincter are seemingly more narrow compared to other breeds will benefit from the use of a smaller diameter endoscope (<6.0 mm).⁴

To obtain adequately sized biopsies, the instrumentation channel should be at least 2.2 mm, preferably ≥2.5 mm. The latest model of endoscopes specifically designed for veterinary use, and suitable for most cats, is a 7.9 mm outer diameter x 1.40 m videoendoscope with an instrumentation channel of 2.8 mm in diameter.⁴

Anaesthesia

General anaesthesia is required for GI endoscopy and intubation with a cuffed endotracheal tube is mandatory because of the risk of gastro-oesophageal reflux. Some anaesthetic agents affect intestinal motility and sphincter function making the passage of the cardia and pylorus potentially more difficult.⁵ Atropine and other anticholinergic drugs should not be used unless necessary to increase heart rate, as these drugs may alter gastric motility patterns and increase pyloric tone. Pure opioid agonists may also increase pyloric tone and should ideally be avoided. Fluid support should be given during anaesthesia; dehydrated animals need to be rehydrated before anaesthesia unless endoscopy needs to be performed as an emergency procedure. In hypoproteinaemic patients colloid administration should be considered to ensure reasonable oncotic pressure.

Anaesthesia monitoring during upper GI endoscopy includes at minimum assessment of heart rate, respiration, blood pressure and pulse oximetry. Overdistension of the stomach during insufflation can cause cardiorespiratory issues.

Biopsies

The quality of endoscopically obtained biopsies greatly influences the likelihood for an accurate histopathological diagnosis of a specific mucosal lesion.^1,2 In general at least six adequate samples need to be collected from the feline gastric or duodenal mucosa to reliably detect abnormalities.^1,2 An adequate biopsy should have a full thickness mucosa and at least three or four intact, if possible contiguous villi.² Samples containing submucosa are preferred. These requirements can be challenging to meet in the feline intestine due to the small intestinal diameter and therefore limited feasibility to direct the forceps tip in to the mucosa at a suitable angle and depth.

After obtaining the specimen, the biopsy forceps are removed from the endoscope and the tissue sample is carefully removed from the jaws. Placing the jaws containing the sample into a container filled with isotonic saline and then “washing-off” the sample by shaking the tip of the forceps helps to avoid damaging the edges of the cups. Specimens should be submitted in fixative, to the pathology laboratory, as quickly as possible for histopathological examination. Submission of a complete history and macroscopic evaluation report to the pathologist is mandatory to obtain best results.

Unfortunately, there’s often a big discrepancy between the macroscopic appearance and final histological diagnosis thus emphasising the absolute importance of collecting endoscopic biopsies during all endoscopic examinations. Differentiation between lymphoplasmacytic IBD and small-cell lymphoma is notoriously difficult and should be confirmed with immunohistochemistry and PARR testing in those clinically suspicious cases.^7,8

Colonoscopy

Large intestinal disease in cats commonly results in large bowel diarrhoea or constipation. It must be remembered, that vomiting is another frequent complaint in cats with large bowel disease. Furthermore, haematochezia can be due to local problems in the large intestine or anorectal disease and must be differentiated from generalised coagulopathies. As mentioned previously, a thorough investigation for systemic diseases is warranted for all these problems including haematology, biochemistry, coagulation testing, faecal analysis and diagnostic imaging.

The commonest abnormal large intestinal disease in cats is some form of colitis. This can be limited to the colon or be part of IBD or even small cell lymphoma of the entire intestinal tract. Colonic tumours, especially lymphoma, can look identical to inflammatory colitis and must be differentiated by histopathology and PARR (+/- immunohistochemistry)^7,8 for definitive diagnosis. Other large intestinal tumours in cats include adenocarcinoma and leiomyosarcoma, both being more focal and often invading the lumen with an irregular proliferative appearance. Other rare findings in cats include ileocolic or ileocaecal intussusception (often diagnosed via ultrasound prior to endoscopy) or rectal stricture.

References

1.  Day, M. J., Bilzer, T., Mansell, J., et al. (2008) World Small Animal Veterinary Association Gastrointestinal Standardisation Group. 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 Standardisation Group. Journal of Comparative Pathology 138, S1–S43.

2.  WSAVA International Gastrointestinal Standardization Group: Washabau RJ, Day MJ, Willard MD, et al. (2010) ACVIM Concensus Statement: Endoscopic, Biopsy, and Histopathologic Guidelines for the Evaluation of Gastrointestinal Inflammation in Companion Animals. J Vet Intern Med. 24, 10–26.

3.  Neiger, R., Robertson E., Stengal C. (2013) Gastrointestinal endoscopy in the cat: Diagnostics and therapeutics. J Fel Med Surg 15, 993–1005.

4.  Stengal C., Robertson E., Neiger R. (2013) Gastrointestinal endoscopy in the cat: Equipment, techniques and normal findings. J Fel Med Surg 15, 977–991.

5.  Smith AA, Posner LP, Goldstein RE et al. (2004) Evaluation of the effects of premedication in gastroduodenoscopy in cats. JAVMA 225, 540–544.

6.  Sabattini, S., Bottero E., Turba M.E., et al. (2016) Differentiating feline inflammatory bowel disease from alimentary lymphoma in duodenal endoscopic biopsies. Journal of Small Animal Practice 57, 396–401.

7.  Kiupel, M., Smedley, R. C., Pfent, C., et al. (2011) Diagnostic algorithm to differentiate lymphoma from inflammation in feline small intestinal biopsy samples. Veterinary Pathology 48, 212–222.

8.  Moore, P.F., Rodriguez-Bertos, A., Kass, P.H. (2012) Feline gastrointestinal lymphoma, mucosal architecture, immunophenotype, and molecular clonality. Veterinary Pathology 49, 658–668.

9.  Washabau RJ, Hasler AH. (1997) Constipation, obstipation, and megacolon. In: August JR (ed) Consultations in Feline Medicine, 3rd ed. Philadelphia, WB Sauders, pp 104–112.