Gastrointestinal endoscopy in dogs

Introduction

Endoscopy is a versatile and minimally invasive technique used to visualize the gastrointestinal (GI) lumen, perform biopsies for further analysis such as histopathology or bacterial analysis, and to deliver treatment for problems such as strictures, polyps or foreign body removal. Although complications of routine endoscopic procedures are rare 1, endoscopy must be performed after a thorough workup and should never be a substitute for a complete history, physical examination, appropriate laboratory procedures and other diagnostic imaging. It is especially important to note that endoscopy and endoscopic biopsy are not always indicated, especially in animals with chronic GI disease, without appropriate therapeutic trials (e.g., deworming, dietary modification, antimicrobial trial). In conjunction with other diagnostic modalities, endoscopy can be both a powerful diagnostic tool for many GI disorders in dogs and an invaluable therapeutic tool, particularly for the retrieval of gastric or esophageal foreign bodies.

This article will consider the benefits of endoscopy in dogs using five case studies. Interventional endoscopy and laparoscopy are beyond the scope of this paper.

Endoscopic equipment

Standard GI videoendoscopy equipment consists of a flexible endoscope, a light source, a videoprocessor, a monitor and an air pump; a videorecording system is frequently connected to the system 2 3. A variety of instruments and accessories are also available, including biopsy forceps, cytology brushes, aspiration/injection needles and foreign body forceps/baskets 4. The main considerations when choosing an endoscope are its length, the outer diameter of the scope, and the diameter of the accessory channel. In dogs, a scope of 8-9 mm diameter and 100-140 cm in length is the most versatile for routine GI endoscopy 2 5, although in the largest breeds this might be too short to pass the ileo-colonic sphincter or the pylorus. It is usually better to select a scope with an accessory channel with a 2.8 mm diameter, which will accept the largest biopsy forceps; this enables a better biopsy quality.

Endoscopic findings should be recorded (ideally including pictures) immediately after the procedure, and standardized reporting forms have been recently proposed (see: www.wsava.org/guidelines/gastrointestinal-guidelines).

Esophageal endoscopy

Indication and patient preparation

The clinical signs of esophageal disease include regurgitation, dysphagia, hypersalivation, coughing, anorexia, and halitosis. Esophageal endoscopic examination should only be performed after obtaining a thorough history, physical examination, thoracic radiographs (including contrast studies if appropriate), and (where indicated) fluoroscopic examination 6. Esophageal endoscopy, sometimes with biopsy, can offer additional information for the diagnosis of foreign bodies (Box 1), strictures (Box 2), esophagitis, granuloma associated with Spirocera lupi, and neoplasia. The healthy esophagus is usually very difficult to biopsy and, in general, if samples can be taken easily it means that the esophageal mucosa is abnormal. Esophageal endoscopy requires general anesthesia (ideally after 8-12 hours fasting), with the patient in left lateral or sternal recumbency. If motility is impaired, such that there is retention of food within the esophagus, a 24-hour fast (or even esophageal lavage after tracheal intubation) may be required to permit successful endoscopy.

Contrast studies, especially using barium, should be avoided before endoscopy because this may impair visualization of the mucosa. If such studies are performed, endoscopy must be postponed for at least 24 hours.

Esophageal endoscopy is best undertaken with a flexible scope; rigid endoscopes may be used to remove large foreign bodies, but increase the risk of esophageal perforation and do not allow for extensive esophageal inspection.

Case 1

An 11-month-old male Pug dog was referred for acute anorexia and regurgitation that had developed 3 days previously. Physical examination and bloodwork were unremarkable. Thoracic radiography identified an unusual opacity in the distal esophagus, strongly suggestive of a bony foreign body (Figure 1). Endoscopy revealed the esophagus to be dilated at the thoracic inlet, with a large bone embedded into the esophageal wall just cranial to the cardia (Figure 2). Despite altering the patient’s position several times, a prolonged endoscopic session failed to retrieve the foreign body, which was eventually pushed into the stomach. Subsequent endoscopic inspection revealed no gastric abnormalities, but considering the severe necrotic ulcerative esophageal lesions and the high risk of esophageal perforation, a gastrotomy was performed only two days later to retrieve the bone. Treatment with omeprazole, sucralfate, antibiotic and methylprednisolone was then administered for 10 days. A postoperative stricture was considered a possible complication, and if clinical signs had persisted a further endoscopic evaluation would have been undertaken, but recovery was uneventful and one year later the dog remained well. 

Case 2

A 9-month-old neutered female Labrador was referred with a history of chronic (one month) regurgitation/vomiting of food, invariably a few minutes after ingestion. Hypersalivation and severe weight loss over the last month were also reported. The dog’s appetite was good but she was unable to keep food down. The dog had been spayed one week before clinical signs appeared. On physical examination, her body condition score was 2/9, with moderate muscle atrophy and dehydration evaluated at 8%. The dog had ptyalism, and palpation of the ventral neck was painful. Bloodwork revealed minor hyperproteinemia, hypernatremia and hypochloremia, compatible with regurgitation/ hypersalivation. Radiography showed the rostral half of the thoracic esophagus to be dilated (Figure 3). With the dog anesthetized and in left lateral recumbency, endoscopy revealed a severe esophageal stricture (Figure 4), possibly secondary to gastroesophageal reflux during the recent anesthetic episode. The tip of the scope could not be passed through the stricture, but the lesion was successfully dilated using a balloon passed through the scope and inflated with water (Figure 5). Caudal to the stricture, severe multifocal ulceration was noted (Figure 6) but no abnormalities were seen within the stomach. In all, three balloon dilations (at intervals of 5- 6 days) were required to obtain satisfactory resolution of the stricture. After the second dilation, fluoroscopy with a barium meal was performed: esophageal motility was normal with moist food, whereas a dry food bolus could not pass the stricture without the dog swallowing water. No gastroesophageal reflux was observed during fluoroscopy. Omeprazole, sucralfate and methylprednisolone were prescribed between each stricture dilation and for two weeks after the last treatment. Three months after the last dilation, the patient was doing well and had gained weight, but only moistened kibble was tolerated, with dry kibble inducing regurgitation.

Gastric endoscopy

Indication and patient preparation

Clinical signs of gastric disease include vomiting, hematemesis, anorexia, nausea, halitosis and/or melena. Gastric endoscopy is particularly recommended for patients with chronic GI disease, but may also be indicated if an acute problem such as a gastric foreign body or ulceration is suspected 7. During the procedure, and especially when there are chronic GI signs, duodenal endoscopy should also be performed. For most cases with chronic vomiting, duodenal (rather than gastric) endoscopy and biopsy will actually provide the diagnosis. Gastric endoscopy with biopsy can typically assist in the diagnosis of gastritis, neoplasia, chronic hypertrophic gastropathy, and ulcers, but (as previously mentioned) endoscopy should only be performed after a thorough work-up. Endoscopy can also enable foreign body retrieval and removal of polyps, or assist in placement of a feeding tube. Endoscopy requires general anesthesia (again ideally after fasting for at least 8-12 hours, and sometimes up to 24-36 hours if delayed gastric emptying is suspected), with the dog placed in left lateral recumbency for the procedure. Contrast studies, especially if using barium, must be performed at least 24-36 hours before endoscopy, as barium can impair visualization of the mucosa and also damage the scope. If necessary, abdominal radiography can be performed before endoscopy to evaluate for residual barium. The main limitation of gastric endoscopy is that it cannot diagnose submucosal disease and GI motility disorders. In addition, the size or shape of some foreign bodies can mean that endoscopic retrieval is impossible, and removal of large trichobezoars can also be very prolonged using a scope; in such cases, surgical removal may be a rational alternative.

Case 3

A 12-year-old intact female Shih Tzu was referred with a history of vomiting daily for the last 9 months, unresponsive to empirical treatment (deworming, antibiotics, dietary trials, gastric protectants). Physical examination revealed a low body condition score (2/9) and 10% body weight loss over the last 3 months. Blood chemistry, CBC, urinalysis, cPL test, fecal parasite screening and thoracic radiography revealed no abnormalities, but folate and cobalamin were both severely decreased (folate was 2.59 ng/mL (reference interval: 5-12) and cobalamin < 150 ng/L (RI: 250-800)). Severe thickening of the gastric wall was noted on abdominal ultrasound, with a focal reaction in the mesenteric fat (Figure 7). Ultrasound-guided fine-needle aspiration of the stomach wall revealed a neutrophilic inflammation. Given the strong suspicion of neoplasia, gastric endoscopy was performed. The esophagus, stomach fundus and the greater curvature were normal, but the lesser curvature and the antrum were rigid and did not dilate on insufflation; there was no ulceration. The severity of the changes to the antrum meant that the scope could not be passed through the pylorus (Figure 8). Histopathology revealed a gastric adenocarcinoma with a very poor prognosis, and the dog was euthanized a few days later (Box 3).

Duodenal/ileal endocopy

Indication and patient preparation

Clinical signs of small intestinal disease include chronic or recurrent vomiting and/or diarrhea, abdominal pain, weight loss, GI bleeding (hematemesis, melena or anemia) or irregular appetite. After excluding systemic disease for dogs with weight loss and chronic diarrhea and/ or vomiting, the decision to perform endoscopic examination 8 is based on:

• The severity of the clinical signs, or if there is GI bleeding

• A non-response to empirical treatment (deworming, dietary modifications, antibiotic trial)

• Laboratory test results (hypoalbuminemia, positive fecal α1-antiprotease, low-serum cobalamin and/or folate with normal TLI)

• Abdominal ultrasound findings (intestinal wall changes or intestinal hyperechoic mucosal striations in a hypoalbuminemic dog 9

Surgical (rather than endoscopic) biopsy may be a better option for diagnosis in some cases, especially if abdominal ultrasound reveals a focal intestinal disease in a segment that cannot be reached by the scope, or if abnormalities are detected deep into the mucosa. Although the least invasive method for obtaining intestinal biopsies, there are certain situations where endoscopy may be contraindicated: e.g., severe clinical conditions such as hypovolemia, hypotension or coagulopathy, or where the patient is at increased risk for anesthesia. In these cases, depending on the clinician’s assessment, medical treatment may be employed to stabilize the patient and endoscopic examination can be delayed. Again, endoscopy should only be performed after a thorough work-up including ultrasound, fecal parasite screening, blood samples (including TLI, folate and cobalamin levels) and urinalysis. The two main limitations are that endoscopic biopsies are superficial and can only diagnose conditions affecting the mucosa, and that it can be difficult to pass the pylorus or the ileocolic sphincter in some patients. An “up-and-down” endoscopic approach is now recommended for dogs with chronic GI disease which require intestinal biopsies, because some diseases processes, including inflammation and lymphangiectasia, can be heterogeneously distributed along the small intestine 10 11. Recent studies have defined the minimal number of adequate endoscopic biopsies necessary to reach a diagnosis 12 13 14 (Table 1). Duodenal/ileal endoscopy requires general anesthesia, and the dog should be fasted for 8-12 hours beforehand and placed in left lateral recumbency; ileoscopy requires a longer fasting period and the preparation employed for colonoscopy (see below) should be followed.

Case 4

A 10-year-old female Border Collie was referred with chronic (3 months) mixed bowel diarrhea, with no response to empirical treatment. Other than a low body condition score, clinical examination was unremarkable. Blood samples revealed hypoalbuminemia (13.3 g/L (23-39)), hypomagnesemia (0.15 mmol/L (0.7-1.0)) and hypocobalaminemia (84 ng/L (200-800)). Bile acid tests, CBC, urinalysis, clotting panel, fecal parasite screening, and thoracic radiography did not reveal any abnormalities. On ultrasound, gastric motility was noted to be abnormal. Considering the severe hypoalbuminemia, bi-directional endoscopy (gastro-duodeno-ileo-colonoscopy) was performed after correcting the hypomagnesemia. Colonic endoscopy was normal. The scope was passed successfully through the ileocolic valve and revealed prominent villi, strongly suggestive of lacteal dilation (Figure 9). The esophagus and stomach were normal but the duodenal mucosa was friable, again with prominent villi. Biopsies were taken from all GI segments, revealing moderate duodenal inflammation and lymphangiectasia and severe changes in the ileum (Box 4). Prednisolone and metronidazole, combined with cobalamin supplementation and a hypoallergenic diet, were initiated. The dog showed both clinical and biochemical improvements within a few days; treatment was withdrawn after six weeks without recurrence of clinical signs.

Colonic endocopy

Indication and patient preparation

Clinical signs of colonic disease include especially signs of large bowel diarrhea, e.g., diarrhea with tenesmus, dyschezia, mucus, and hematochezia. Other signs of colonic disease include vomiting, constipation, hematochezia without diarrhea and mixed bowel diarrhea. Vomiting may be seen in up to 30% of colonic disease cases, and hematochezia without diarrhea is reported in 70% of dogs with rectal tumors 15. Colonic endoscopy requires general anesthesia, again with the dog in left lateral recumbency. Patient preparation involves complete rectal and colonic fecal evacuation, partly because residual fecal material impairs visualization and may prevent complete examination up to the ileo-colonic sphincter, and partly because ileal scoping is now recognized as an essential part of the endoscopic work-up in patients with small bowel signs 16. There are various ways to prepare the patient; the authors prefer a two-stage protocol:

• The dog must only be fed a low-residue diet (e.g., boiled chicken or white fish) for 4-5 days before endoscopy.

• The patient is hospitalized the day before the procedure and fasted; enemas are administered 24 and 12 hours prior to colonoscopy, with a third enema just before the dog is anesthetized.

Each enema should be performed with 30-50 mL/kg of warm water, without soap. Other type of enema solutions (e.g., sodium phosphate) are not recommended, as life-threatening metabolic disorders with severe hypernatremia, hypocalcemia, hyperphosphatemia, and polycythemia have been reported 17. One study suggested that polyethylene glycol (PEG)-containing electrolyte solution given orally is preferable to administration of multiple enemas when preparing dogs for colonoscopy 18. However, large volumes of PEG are required (> 50 mL/kg) which can be difficult to administer, often necessitating nasogastric or orogastric intubation.

Case 5

A 9-month-old male Boxer was referred for chronic large bowel diarrhea with hematochezia, tenesmus, and fecal mucus for 5 months, with no response to empirical treatment (fenbendazole, toltrazuril, metronidazole, enrofloxacin). Initially, the entire litter had shown the same signs, but the other puppies had improved when treated with enrofloxacin. No weight loss or failure to grow was noted, and the dog was correctly vaccinated and dewormed. There was no abnormality on physical examination, including rectal examination. Fecal parasite screening, CBC, biochemistry, TLI/folate/cobalamin levels, and urinalysis were normal. Abdominal ultrasound revealed submucosal vessels, with several disseminated nodules and petechiae in the descending colon (Figure 10). These findings were suggestive of severe colonic inflammation or (less likely) neoplasia; the dog’s age and breed suggested that granulomatous colitis was the most likely diagnosis, and this was confirmed on biopsy (Box 5). Enrofloxacin was prescribed for 6 weeks, along with a hypoallergenic diet, and the patient dramatically improved within 5 days; no relapse has been reported several years after the diagnosis.