1. Introduction

Gastroduodenoscopy is an important diagnostic procedure in dogs and cats with chronic gastrointestinal disturbances. It allows direct assessment of the esophageal, gastric and duodenal mucosa in combination with taking fluid samples and mucosal biopsies for further microbiological and histological examination. Histology is needed to reveal different types of chronic inflammatory bowel diseases such as lymphocytic-plasmocytic, eosinophilic, histiocytic or granulomatous enteritis. It is also possible to diagnose tumors and intestinal lymphangiectasia with gastroduodenoscopy when the proximal parts of the small intestine are involved in the disease process.

Furthermore, gastroduodenoscopy can be extended to diagnose diseases of the biliary tract and the exocrine pancreas via endoscopic retrograde cholangio-pancreatography (ERCP). ERCP is an imaging technique that combines endoscopy and fluoroscopy. Morphological changes of the biliary tract and exocrine pancreas can be visualized by endoscopic guided retrograde filling of both duct systems with contrast medium. This imaging technique has been successfully used in people already for decades and has currently been introduced into veterinary medicine.

Endoscopically guided therapeutic interventions in the upper gastrointestinal tract include foreign body removal out of esophagus and stomach, balloon dilation of esophageal strictures, the placement of percutaneous gastric and jejunal tubes for enteral feeding and possibly ERCP guided sphincterotomy of the major papilla in patients with biliary outflow problems.

2. Gastroduodenoscopy-indication, contraindication, complication and performance

Indications for gastroduodenoscopy in dogs or cats are:

 Chronic or recurrent vomiting / regurgitation

 Hematemesis / melaena

 Chronic or recurrent small intestinal diarrhea

 Chronic or recurrent abdominal pain

 Anorexia and weight loss

 Suspected esophageal / gastric foreign body

The following technical requirements are needed to perform a gastroduodenoscopy:

 Flexible fiber optic or video gastroscope

 Adjustable light source, insufflation-, suction- and rinse-device

 Biopsy forceps

 Foreign body removal devices (forceps, noose, basket)

 Container with 4% formaldehyde solution and blotting paper for storage/transport of mucosal biopsies

 Sterile containers for material (fluid, biopsies) for microbiological examinations

Before starting an endoscopy, contraindications such as increased risk for anesthesia, hemorrhagic diathesis, and esophageal, gastric or intestinal perforation have to be excluded.

Possible complications include excessive bleeding, perforation and gastric torsion. However, with careful use of endoscopy these complications are extremely rare. Using ERCP for the diagnosis and treatment of biliary and pancreatic diseases, complications can be acute pancreatitis and sphincterotomy induced perforation as described in human medicine.

Limitations of diagnostic gastroduodenoscopy are caused by anesthesia which influences the assessment of gastrointestinal peristalsis and secretion, by the limited length of the endoscope that allows only the assessment of proximal parts of the intestine, and by the size of the biopsies allowing only the histological evaluation of the mucosa and submucosa but not of the muscularis.

Total anesthesia is necessary for gastroduodenoscopy to avoid injuries to the patient and the expensive endoscope. In dogs, L-methadone should not be used for anesthesia because it can cause a spasm of the pylorus which leads to difficulties in endoscopic passage of this anatomic structure. Diazepam can be used for premedication and ketamine with xylacine for induction of anesthesia in dogs. An alternative is the premedication with medetomidine and butorphanole followed by induction with propofol. In cats, it is possible to use intravenous combination anesthesia such as ketamine with xylacine, ketamine with diazepam, or butorphanole with medetomidine and ketamine. In case of an expected vagal induced bradycardia, atropine can be added to the premedication. For maintenance of anesthesia, isoflurane inhalation is used after orotracheal intubation of the dog or cat. It is advisable to intubate all patients undergoing a gastroduodenoscopy to avoid aspiration pneumonia during the procedure.

Gastroduodenoscopy can be performed after a starvation phase of 12-18 hours. The anesthetized patient has to be placed in left recumbency to allow an easy visualisation and passage of the pylorus. To avoid damage to the endoscope in case of an unexpected awakening of the patient, the mouth should be secured with a gag and a rope. During the procedure, the endoscope should never be pushed forward without a proper view to avoid possible perforation in case of ulcerations. The endoscopic examination includes the assessment of intraluminal contents (fluids, foreign bodies, bezoars, feces), of mucosal conditions (color, thickness, erosions, ulcers, polyps, tumors), and of the wall elasticity as an indicator for intramural changes (inflammation, tumor).

Endoscopy always should be completed with the withdrawal of 6-8 biopsies from both the gastric and the duodenal mucosa. Biopsies should be taken at the end of the examination to avoid bleeding artifacts during the visual assessment of the mucosa. The size of the biopsy is dependant on the size and type of the biopsy forceps and the biopsy technique. The size of a biopsy forceps is limited to the diameter of the endoscope's working channel. It is advisable to use the biggest possible biopsy forceps with a tip that flexes to the side when the forceps opens. This allows an adjustment of the forceps to the mucosa especially in the duodenum. Bigger pieces of mucosa can be gained when the previously inflated air is sucked out of the duodenum shortly before closing the forceps. For gastric biopsies, it is helpful not to inflate the stomach to much because biopsies are easier to take from the tip of gastric folds. Mucosal biopsies should be placed on a filter paper and into a biopsy container before placing them into formaldehyde. This measure helps to place duodenal villi in longitudinal axis for histological assessment and to avoid the shrinkage of the mucosal tissue as an effect of formaldehyde fixation.

Withdrawal of duodenal content for quantitative analysis of bacterial colonization in the small intestine is suggested to be the gold standard for the diagnosis of small intestinal bacterial overgrowth. However, technical difficulties of this technique have led to its limited use in clinical practice.

3. Endoscopic retrograde cholangio-pancreatography (ERCP)

Recent experimental and clinical studies have revealed that it is possible to use ERCP as a diagnostic tool in dogs weighing > 10 kg. With ERCP it is possible to diagnose pathological changes of the duodenal papillae and the biliary and pancreatic duct systems as signs of malformation, inflammation or neoplasia.

For ERCP, a side view endoscope, fluoroscopy equipment and a video recorder or computer for documentation are needed. Further instruments are special ERCP catheters with distal marking lines and a contrast medium (e.g., iomeprol, Imeron® 300, Bracco-Byk Gulden). When the side view endoscope is placed in the proximal duodenum, the dog is repositioned from left lateral to dorsal recumbency so that the optic of the side view endoscope points to the minor or major papilla. The more caudal situated minor papilla is cannulated with the ERCP catheter before the major papilla to avoid bleeding artifacts at the major papilla that prevent the visualisation of the minor papilla. After insertion of the catheter into the minor papilla 1.0-2.0 ml contrast medium is administered into the pancreatic duct system under fluoroscopy control. Filling of pancreatic parenchyma with contrast medium must be avoided since this can induce acute pancreatitis as known from humans. For contrast filling of the canine bile duct system and gallbladder, 20.0-40.0 ml contrast medium can be administered through the major papilla by ERCP-catheter.

First studies have shown that ERCP can be performed successfully in dogs and provides a good visualization of the common bile duct and the accessory pancreatic duct. The technique allows an objective measurement of duct length and diameter with a relatively low risk of ERCP induced pancreatitis. The clinical use of ERCP in a limited number of clinical cases has already shown the possibility to reveal duct abnormalities by this technique.

4. Therapeutic gastroduodenoscopy

Endoscopic withdrawal of foreign bodies is indicated when swallowed objects are exclusively in parts of the gastrointestinal tract that can easily be reached with the endoscope such as esophagus or stomach. It is contraindicated when esophageal foreign bodies are very sharp or can cause esophageal perforation. In those cases and if the foreign objects are already in the intestine, surgical intervention is the treatment of choice. Otherwise it is relatively easy to remove foreign objects such as wood pieces, bones, fishing hooks, stones, small balls, coins and plastic material. To avoid a closure of the lower esophageal sphincter or an injury of the esophagus while removing sharp foreign objects, a bell shaped plastic cover can be placed on the tip of the endoscope. The foreign body can be pulled into the cover for safe removal.

For the dilation of benign esophageal strictures endoscopic guided balloon dilation or bougienage can be used. Balloon dilation is the preferred technique using "through the scope" balloon catheters or catheters that are placed parallel to the endoscope into the esophagus. The balloon diameter has to be adjusted to the size of the patient's esophagus and the stricture in order to gain treatment success but not to rupture the esophagus. It is advisable to repeat the balloon dilation 1-3 times every 2-4 days to avoid an intense re-stenosis by scarring of the balloon induced tear. In severe cases, the local injection of methylprednisolone is thought to be useful. However, there is some discussion about the real benefit of glucocorticoid administration after balloon dilation. Further post-dilation treatment includes 48 hours fasting, blockers of gastric secretion (H2-blockers, omeprazole), sucralfate, and if indicated prokinetics (e.g., cisapride).

Endoscopy guided placement of a percutaneous gastric tube (PEG-tube) is an alternative to its surgical or "blind" placement. It is indicated in dogs and cats with expected long lasting difficulties in voluntary eating or with severe catabolic diseases or metabolic disturbances such as feline hepatic lipidosis. Endoscopic guidance has the advantage of secure placement of the percutaneous tube under vision control especially for veterinarians who are just beginning to use this minimal invasive technique of forced enteral feeding.

Endoscopic placement of jejunal feeding tubes for post-gastric feeding has recently been described but its use is still limited to specialized clinics.

References

Books

1.  Cotton, PB, Williams CB: Practical gastrointestinal endoscopy. 4^th ed., Blackwell Science, Oxford, 1996

2.  Kraft W. Tierärztliche Endoskopie. 1^st ed., Schattauer, Stuttgart, 1993

3.  Tams T.R. Small Animal Endoscopy, 2^nd ed., Mosby, St. Luis, 1999

Articles

1.  Armstrong PJ, Hardie EM. Percutaneous endoscopic gastrostomy. A retrospective study of 54 clinical cases in dogs and cats. J Vet Intern Med. 1990 Jul-Aug; 4(4): 202-6.

2.  Dargent F. Esophagitis and esophageal stricture-a practical approach for diagnosis and treatment. Proceedings of the 14^th ECVIM-CA Congress, Barcelona, 2004: 50-51

3.  German AJ, Day MJ, Ruaux CG, Steiner JM, Williams DA, Hall EJ. Comparison of direct and indirect tests for small intestinal bacterial overgrowth and antibiotic-responsive diarrhea in dogs. J Vet Intern Med. 2003 Jan-Feb; 17(1):33-43.

4.  Heuter K. Placement of jejunal feeding tubes for post-gastric feeding. Clin Tech Small Anim Pract. 2004 Feb; 19(1):32-42.

5.  Jergens AE. Percutaneous endoscopic jejunostomy tubes: clinical applications and technique. Proceedings of the 20th ACVIM Congress, DALLAS, TX 2002, 509-10

6.  Sellon RK, Willard MD. Esophagitis and esophageal strictures. Vet Clin North Am Small Anim Pract. 2003 Sep; 33(5):945-67.

7.  Spillmann T, Happonen I, Sankari S, Wittker A, Kähkönen T, Westermarck E. Evaluation of serum values of pancreatic enzymes after endoscopic retrograde pancreatography in dogs. Am J Vet Res, 2004,65: 616-19

8.  Spillmann T, Happonen I, Kähkönen T, Fyhr T, Westermarck E. Endoscopic retrograde cholangio-pancreaticography in dogs, Vet Radiol & Ultrasound 2004, in press

9.  Zoran DL. Gastroduodenoscopy in the dog and cat. Vet Clin North Am Small Anim Pract. 2001 Jul; 31(4):631-56.