Clinical indications and techniques for upper and lower GI endoscopy (Proceedings)

Introduction

In recent years, the availability and extended use of rigid and flexible endoscopy has led to a marked increase in diagnostic procedures involving visualization and biopsy of the upper and lower gastrointestinal (GI) tract in domestic animals. Endoscopy provides rapid, minimally invasive examination of mucosal surfaces and permits procurement of tissues for histologic and cytologic examination, or of fluid specimens for laboratory evaluation.

Key to the success of GI endoscopy in detecting mucosal disease is proper biopsy technique. Pertinent considerations include 1) the organ being sampled, 2) nature of the suspected lesion, 3) presence of focal versus diffuse mucosal disease, 4) selection of biopsy instrumentation, and 5) post-biopsy specimen handling considerations.

Esophagoscopy And Gastroscopy

Normal Mucosal Appearance

The endoscopic appearance and texture of mucosal surfaces varies. The normal esophageal mucosa is pale, white-to-glistening pink. Small amounts of froth or bile-stained gastroduodenal fluid are occasionally seen. The distal one-third of the feline esophagus has prominent circumferential mucosal folds which are not observed in the dog. This is the result of the change from striated muscle (proximal two-thirds) to smooth muscle (distal one-third) which occurs in the feline esophagus. The tunica muscularis of the canine esophagus consists entirely of skeletal muscle. The gastroesophageal junction is usually highlighted by a mucosal color change to bright pink or red and is considered normal in both the dog and cat.

Gastric mucosa is normally smooth and glistening pink with rugal folds which are uniform in size, shape, and distensibility. Submucosal blood vessels are typically seen in the gastric body region following insufflation of air. The pyloric antrum is delineated by the presence of the incisura angularis, and is characterized by a paler pink mucosal appearance and absence of rugal folds. Antral peristaltic waves are commonly observed. In most animals, the pylorus is readily identified and variable degrees of pyloric dilation will be seen.

Abnormal Mucosal Appearances

Gross mucosal abnormalities are common and range from the obvious, such as intraluminal masses, to discrete erosions. Mass lesions are usually seen with infiltrative mucosal diseases (malignant neoplasia, benign polyps, inflammatory disorders) and may be pedunculated or sessile. Masses should be biopsied deeply to avoid necrotic surface debris and superficial cells which may obscure a correct diagnosis. If diffuse neoplasia is suspected, multiple biopsy specimens deep within the lamina propria should be obtained from both normal and abnormal appearing mucosa.

Consistent endoscopic terminology has been proposed to aid in lesion description and the formulation of a definitive diagnosis. Erythema denotes mucosal redness which may be pathologic or a normal physiologic response to endoscope induced trauma, blood flow changes associated with anesthesia, or warm water enemas. Friability describes the ease with which the mucosa is damaged by contact with the endoscope or biopsy instrument. Alterations in mucosal texture are described as increased granularity. Granularity of the intestinal mucosa may be influenced by gland height and crypt depth as the light of the endoscope reflects off these structures.

Mucosal ulceration - erosion is defined as an endoscopically visible breach in mucosal integrity, often associated with active hemorrhage. Ulcers are typically focal, crateriform, well-circumscribed lesions which extend deeply into the adjacent mucosa and contain central fibrinous exudate. Erosions are discrete, superficial mucosal defects which do not have raised margins or necrotic centers. Ulcers and erosions are characteristic of inflammatory and neoplastic lesions. Erosive lesions are biopsied directly without complication. Ulcerative lesions are best biopsied by obtaining specimens from the ulcer rim as it interfaces with adjacent tissue. Mucosal biopsies from tissue surrounding an ulcer should also be obtained to characterize benign from malignant ulcer disease.

Endoscopic Biopsy Of The Esophagus

Indications: Clinical signs of dysphagia, regurgitation, excessive salivation, vomiting, hematemesis, suspicion of stricture, diverticulum, or foreign body.

Patient preparation: Withhold food for 12-18 hours. Animals having esophageal retention of ingesta or barium contrast may require additional time.

Instrumentation: Flexible endoscopy is preferred. Biopsy accessories should include serrated jaw pinch forceps (most useful), foreign body graspers, and a balloon catheter for dilatation of strictures. Mucosal biopsy of the esophagus is uncommonly required except for intraluminal mass lesions.

Abnormal findings: Mass lesions (neoplastic most commonly), esophagitis (mucosal erythema, hemorrhage, erosions), stricture, foreign body, focal or generalized dilatation, and perforation.

Biopsy recommendations: It is difficult to obtain esophageal biopsy specimens since the mucosa is tough and the biopsy instrument cannot be easily positioned perpendicular to the mucosal surface. Biopsy of mass lesions with pinch forceps often yields only superficial epithelia. Mass lesions should be biopsied deeply to avoid necrotic surface debris and superficial cells which may obscure a correct diagnosis. Always obtain specimens from the border delineating grossly normal mucosa from the abnormal mass. In my experience, exfoliative cytology of mass lesions is as or more useful than histopathology given the above limitations.

Endoscopic Biopsy Of The Stomach

Indications: Clinical signs referable to gastric diseases, including anorexia, weight loss, chronic vomiting, hematemesis, and melena. Specific diseases diagnosed via gastroscopy include chronic gastritis, gastric ulcer/erosions, foreign bodies, gastric nematodes, and pyloric mucosal hypertrophy.

Patient preparation: Withhold food for 12-18 hours. Animals having gastric retention of ingesta or barium contrast will require that food be withheld for 24-36 hours.

Instrumentation: Flexible endoscopy to visualize the cardia, fundus, body, antrum, and pyloric regions of the stomach. Instrumentation should include serrated jaw pinch forceps for mucosal biopsy and retrieval forceps (three-pronged and basket types) for removal of foreign bodies.

Abnormal findings: Mucosal granularity (eg, increased mucosal texture seen with inflammatory or neoplastic infiltrative diseases), increased tissue friability (denoted by excessive mucosal hemorrhage following contact with the endoscope or biopsy instrument), excessive erythema (quite subjective), mass lesions, rugal distortion, ulcer/erosions, incomplete gastric distention, retained gastric contents, foreign body, and intraluminal parasites.

Biopsy recommendations: Gastric biopsies are always obtained regardless of mucosal appearance. Serrated jaw pinch forceps produce the greatest tissue purchases. Six to eight good quality biopsy specimens should be procured. Focal lesions such as masses, erosions, and ulcers should be biopsied directly. Masses are repeatedly biopsied deeply, and at the junction of normal from abnormal appearing mucosa. Ulcerative lesions are best biopsied by obtaining specimens from the ulcer rim as it interfaces with adjacent tissue. Brush cytology may allow for rapid tentative diagnosis of mucosal disease. In the absence of gross mucosal abnormalities, obtain multiple random biopsies from the rugal folds of the gastric body. The antrum is not routinely sampled unless gross lesions are present.

Enteroscopy And Colonoscopy

Normal Mucosal Appearance

The duodenal mucosa has a more granular texture, as compared to other alimentary tract organs, due to its prominent villous architecture. Color of the duodenal and jejunal mucosa varies from pale pink to yellow-red in animals having active bile discharge. Submucosal lymphoid aggregates appear as oval, slightly depressed mucosal structures present along the descending duodenum and should not be interpreted as small ulcers. Other mucosal structures which should not be mistaken as lesions include the major duodenal papilla (present in the dog and cat) and minor duodenal papilla (present only in the dog).

Normal colonic mucosa is pale pink, smooth, and glistening. Submucosal blood vessels are readily observed with adequate insufflation. Lymphoid aggregates, 3-5 mm in diameter and umbilicated, are diffusely abundant in the aboral colon. Visual inspection of the cecum and ileocolic valve should be performed in all patients undergoing full colonoscopy. Parasitism, cecal inversion, ileocolic intussusception, inflammatory bowel disease, and neoplasia may cause mucosal lesions in this region.

Endoscopic Biopsy Of The Small Intestines

Indications: Patients having clinical signs of small intestinal disease, including chronic small bowel diarrhea, weight loss, alterations in appetite (most commonly anorexia), vomiting, and melena. Specific small intestinal diseases diagnosed via enteroscopy include inflammatory bowel disease (IBD), intestinal neoplasia, duodenal ulcer/erosions, and gastrointestinal Histoplasmosis. Enteroscopy is particularly useful in obtaining small bowel biopsies in protein-losing enteropathy patients where poor wound healing subsequent to surgery may be of concern.

Patient preparation: Withhold food for 12-18 hours for upper small bowel examination. Retrograde ileoscopy will require more extensive patient preparation (see colonoscopy).

Instrumentation: Flexible endoscopy is required to traverse the pylorus and to visualize the descending duodenum. The jejunum is often accessible to endoscopic evaluation in small dogs and most cats. Serrated jaw pinch forceps (without bayonet) are most useful for small bowel biopsy procedures.

Abnormal findings: Alterations in mucosal texture (increased granularity), friability, and hyperemia are commonly observed. Increased granularity, friability, and erosions are often associated with mucosal inflammation seen with IBD and intestinal neoplasia. Ulcers (uncommon) and erosions (more common) are characteristic of inflammatory and neoplastic lesions. A milky-white mucosal appearance or milky exudate within the intestinal lumen may be seen in dogs with lymphangiectasia.

Biopsy recommendations: Duodenal/jejunal biopsies are always obtained regardless of mucosal appearance. Duodenal tissue is normally quite friable and good technique is essential! Serrated jaw pinch biopsy forceps should be used to obtain 10-15 good quality specimens. Focal lesions are biopsied directly. The best biopsies are obtained by directing the instrument perpendicular to the mucosal surface. Alternatively, "blind" biopsies may be procured by passing the biopsy forceps as far as possible down the lumen until resistance is met. Due to their friability, special care is advised when removing small intestinal specimens from biopsy forceps.

Endoscopic Biopsy Of The Large Intestines

Indications: Clinical signs of chronic colonic disease including large bowel diarrhea (exhibited by tenesmus, dyschezia, hematochezia, or the passage of mucoid feces). Colonoscopy is particularly useful in the diagnosis of IBD (lymphocytic-plasmacytic colitis) or rectal masses in both dogs and cats.

Patient preparation: Withhold food for 18-24 hours. In dogs, I prefer to administer two doses of a colonic electrolyte lavage solution (GoLYTELY, 20 ml/kg/dose given 4-6 hours apart orally) the afternoon before an AM endoscopy. The morning of the procedure, I give a warm-water enema to both dogs and cats.

Instrumentation: Flexible endoscopy allows for visualization of all colonic regions as well as retrograde ileoscopy. Biopsy instrumentation should include serrated jaw pinch biopsy instruments.

Abnormal findings: Similar as for enteroscopy including increased mucosal granularity, increased friability, and the presence of ulcer/erosions. Loss of submucosal vascularity is a significant finding and may be caused by mucosal edema, the accumulation of exudate (blood, mucous, necrotic debris), or infiltration of inflammatory or neoplastic cells. Masses and colonic nematodes (Trichuris vulpis) are less common endoscopic observations.

Biopsy recommendations: Colonic biopsies are always obtained regardless of mucosal appearance. Flexible endoscopy is preferable since examination and biopsy of the transverse and ascending colons may also be performed. Focal lesions are biopsied directly. In the absence of gross mucosal abnormalities, obtain 3-4 biopsy specimens from each colonic region using serrated jaw pinch biopsy forceps.

Suggested Readings

1. an der Gaag I. The role of biopsy in the diagnosis of gastrointestinal conditions in small animals. Veterinary Annual 34th issue; 1994:141-154.

2.Willard MD. Colonoscopy. In Tams TR (ed): Small Animal Endoscopy, Philadelphia, CV Mosby Co, 1999, pp 217-245.

3. itt ME. Biopsy of the gastrointestinal tract. In Bonagura JD, Kirk RW (eds): Current Veterinary Therapy XII, Philadelphia, WB Saunders, 1995, pp 675-678.

4. ams TR. Endoscopic examination of the small intestine. In Tams TR (ed): Small Animal Endoscopy, Philadelphia, CV Mosby Co, 1999, pp 173-216.