Small diameter flexible endoscopes facilitate the investigation of regurgitation, chronic vomiting, haematemesis, melaena and small and large bowel diarrhea. Mucosal surfaces can be directly visualised and biopsies obtained without recourse to surgery. Therapeutic applications include foreign body removal, stricture dilatation and placement of feeding tubes (Table 1). This presentation will review the indications for, and techniques of, diagnostic endoscopy in the upper gastrointestinal tract in the dog and cat. Photographs of a wide range of gastrointestinal lesions can be found in endoscopic atlases e.g., Tams and Brearley.

Equipment

Endoscopes used for examination of the gastrointestinal tract (GIT) in the dog and cat generally have a working shaft length of at least one meter (at least 130 cm is required in big dogs), an outside diameter of 5.9 to 9.8 mm and a flexible, maneuverable tip capable of four-way deflection. They should also have a wide field of view (> 100°) and channels for insufflation of air, suction and passage of biopsy instruments (2.0-2.8 channel). All these requirements are generally met by modern pediatric endoscopes.

Patient Preparation

Food is withheld for at least 12 hours before upper GI endoscopy. A longer period may be required in patients with gastric retention or foreign bodies. All flexible endoscopic procedures are performed under general anaesthesia. The author generally avoids premedication with atropine for gastroscopy and duodenoscopy because of its potential adverse effects on gastrointestinal motility and intestinal secretion. A mouth gag is essential for esophagoscopy and upper gastrointestinal endoscopy.

Esophagoscopy

The investigation of regurgitation is the major indication for esophagoscopy. A careful history and oro-pharyngeal exam usually allows regurgitation to be distinguished from vomiting or dysphagia. Table 2 summarises the esophageal lesions which endoscopy is useful in detecting. Survey radiographs of the chest are obtained before esophagoscopy. The information provided by radiographs is complementary to esophagoscopy, and can reveal megaesophagus, foreign bodies, perforations, periesophageal masses and aspiration pneumonia. Functional disorders of the esophagus are better evaluated with radiographic contrast studies than endoscopy.

Technique and Findings

Animal in left lateral recumbency with a mouth gag is inserted. The tip of the endoscope is lubricated, passed blindly into the proximal esophagus and then advanced down the esophagus under direct visualisation whilst insufflating air.

Abnormal findings include retained food, fluid, parasites and foreign bodies. Reddening, roughening, petechiation and ulceration may indicate esophagitis. Perforations, constrictions secondary to vascular ring anomalies or strictures and esophageal masses can also be detected. Eversion of the gastric mucosa into the esophagus (gastro-esophageal intussusception) is uncommonly encountered and may resolve with insufflation and gentle insertion of the scope. Redundancy of the esophageal mucosa suggests dilatation of the esophagus, although this is often difficult to confirm endoscopically.

Gastroscopy

The investigation of chronic vomiting (intermittent or persistent), haematemesis and melaena are the major indications for gastroscopy. Endoscopically detectable gastric lesions that can cause chronic vomiting or blood loss are summarised in Table 2. A work up to rule out underlying metabolic disorders (haemogram, profile, urinalysis) and survey abdominal radiographs, should be obtained prior to pursuing a primary gastric disorder. Endoscopy enables detailed examination and sampling of the gastric mucosa with minimal patient discomfort and is generally accepted as a better method than radiographic contrast studies for evaluating mucosal abnormalities. Radiographic contrast studies (± fluoroscopy) are a good way of examining functional or emptying disorders of the stomach. Some patients require both endoscopy and radiography to adequately evaluate their gastric disorder. Before undertaking gastroscopy, a working knowledge of the normal anatomy of the stomach is required.

Technique and Findings

Entry to the stomach is gained by passing the endoscope down the esophagus (see above), centering it on the orifice of the gastro-esophageal sphincter (which is usually closed) and advancing whilst insufflating air. As duodenal entry is hindered by lingering in the stomach a thorough examination of the stomach is performed after duodenoscopy. After duodenoscopy, the pyloric sphincter and pylorus are inspected and the endoscope withdrawn to the incisura angularis. Retroflexing the scope and pulling it back to visualize the cardia is an easy way of reorienting yourself if you are lost in the stomach!

Abnormal findings such as retained food, fluid, parasites, foreign bodies and pyloric obstruction are usually readily apparent. The mucosal surface should be examined carefully for evidence of reddening, roughening, petechiation, haemorrhage, increased granularity or friability, rugal and mucosal thickening or distortion, erosions, ulcers and mass lesions. Alterations in distensibility of the gastric wall suggest submucosal or extragastric causes.

Duodenoscopy

The investigation of small bowel diarrhea, protein losing enteropathies, chronic vomiting (intermittent or persistent) and melena are the major indications for duodenoscopy (Table 2). Patients with small bowel diarrhoea should undergo a work up to detect underlying metabolic, parasitic, infectious and pancreatic causes before pursuing primary intestinal disorders. The diffuse nature of many intestinal causes of small bowel diarrhoea and protein losing enteropathies means that duodenoscopy may enable a diagnosis to be obtained without recourse to surgery. Combined gastroscopic and duodenoscopic examination enables lesions to be localised to the stomach, duodenum or both. Radiographs obtained before duodenoscopy are usually low yield but are performed to screen for partial obstructions caused by intussusceptions or foreign bodies, peritonitis, mass lesions and abnormalities of the liver, kidney and spleen. Contrast radiography is expensive and time consuming but may help detect intestinal lesions distal to the duodenum.

Technique and Findings

Gross abnormalities such as undigested food, large amounts of fluid, tumors, foreign bodies and parasites are easily detected. The mucosa should be evaluated for increased redness or pallor, petechiation, erosions, ulcers and increased granularity. Deflation and inflation of the duodenum enables detection of alterations of distensibility and mucosal irregularities. Biopsy forceps are used to determine if the mucosa is excessively friable.

Colonoscopy

As the diagnostic and therapeutic approaches to large and small intestinal disease are different, it is important to localize the likely site of disorders to the large or small bowel. Characteristic findings of large bowel diarrhea are increased frequency, urgency, tenesmus, low faecal volume and the presence of mucus and fresh blood. Vomiting and weight loss are rarely present.

Differential diagnoses of large bowel diarrhea include infectious (Campylobacter, Salmonella), parasitic (whipworms, Giardia), inflammatory (eosinophilic, lymphoplasmacytic, granulomatous, histiocytic, neutrophilic), neoplastic (polyps, adenocarcinoma, lymphosarcoma), anatomic (intussusception, stricture) and functional causes. Large bowel diarrhoea can also occur in association with systemic disorders (pancreatitis, uraemia, hypothyroidism, hypoadrenocorticism) and small intestinal disease.

A full physical and rectal examination are essential to rule out extracolonic disorders with presenting signs similar to large bowel disorders, e.g., prostatomegaly, perineal hernia and perianal problems. A faecal sample should be examined for parasites and cultured for Campylobacter and Salmonella. If signs are severe or chronic, a biochemical profile, urinalysis and complete blood count should be submitted to screen for systemic disease. In many animals with large bowel diarrhoea the physical exam, faecal exam and blood tests are normal, enabling the clinician to localise the problem to the large bowel. The next step in the investigation of large bowel diarrhea is proctoscopy/colonoscopy.

Technique and Findings

Colonoscopy is usually performed in animals with severe signs and those who have failed initial therapy. Routine bloodwork, fecal examination, cultures etc. should be performed prior to colonoscopy. Survey radiographs of the abdomen can also be obtained prior to colonoscopy. Thirty-six to 48 hours of starvation and enemas (2-3 warm water the evening and morning before the procedure) are necessary to prepare the colon for viewing. Oral colonic lavage solutions may also be used. 'GoLYTELY' has been recommended for use in dogs (26 ml/kg by stomach tube twice, one hour apart, 12-18 hrs before endoscopy). Colonoscopy is undertaken with a rigid proctoscope or a flexible endoscope with the animal under general anaesthesia. Fiberoptic endoscopes allow the caecum to be visualised. The animal is placed in left lateral recumbency. A digital examination is performed prior to inserting the scope. The scope is advanced as far as possible. With the patient in left lateral recumbency the caecum is usually on the right hand side and appears more open than the ileocolic orifice which is often clamped shut. Entry to the ileum may be achieved by inserting the forceps through the ileocolic orifice, using them as a guide wire to gently advance the endoscope. Biopsies are taken while withdrawing the scope. Do not overinsufflate the colon with air during/after taking biopsies. Biopsies should always be taken, even though the colon looks grossly normal.

Abnormalities include poor distensibility, ulceration, erosion, masses and increased friability. Gross abnormalities such as polyps and ulcers are easily detected, but may be obscured by feces if the colon is poorly prepared. Careful evaluation of the colonic vasculature is advocated in patients with unexplained frank blood loss into the stool--angiodysplasia has been reported as a cause in dogs.

Biopsy Techniques

Biopsy forceps are advanced carefully down the biopsy channel with the endoscope tip in neutral position. If any resistance is met, the forceps must be withdrawn and the endoscope straightened prior to further advancement. When the forceps are seen protruding from the endoscope they can be opened and pushed against the area to be biopsied. It is best to be as perpendicular to the biopsy site as possible before closing the forceps. Overdistension flattens the mucosa and makes it hard to take biopsies. An estimation of mucosal friability should be made while taking biopsies. Pinch biopsy forceps only penetrate the superficial mucosa but repeated biopsies at the same site allow deeper layers to be evaluated. Biopsies must be minimally handled and placed immediately in formalin for histopathologic examination. Impression smears of biopsies may reveal the presence of inflammatory and neoplastic cells, and pathogenic bacteria or fungi.

Table 1. Indications for GI endoscopy.

Table 2. Utility of endoscopy for investigation of esophageal, gastric and small intestinal abnormalities.