Overview of Endoscopy Systems

Endoscopy is a medical procedure that permits the clinician to examine internal structure and to perform diagnostic and therapeutic procedures in a minimally invasive manner. The term endoscope originally referred to first-generation flexible gastroscopes, which were also used for upper and lower gastrointestinal (GI) endoscopy, as well as bronchoscopy, in larger patients. The term endoscope now refers to all sizes and styles of optical instruments used for internal exams, including both rigid and flexible gastroscopes, bronchoscopes, cystoscopes, arthroscopes, laparoscopes, and otoscopes.

A basic endoscope system typically consists of the endoscope, light source, air pump, video camera (or camera processor), and video monitor. Although it is possible to perform endoscopy without a camera and monitor, the current availability, advantages, and superiority of video systems have rendered fiberscopes and their eyepieces much less popular. The endoscope, light source, camera, and monitor comprise the “imaging chain,” which is ultimately responsible for creating the image viewed on the monitor. All of the components contribute to the displayed image, whose quality can only be as good as the weakest link in the chain.

Figure 27-1 illustrates a simple gastrointestinal endoscope “tower.” A mobile cart improves portability and accessibility, and should be capable of accommodating all of the components of the endoscope system. Much of the equipment (e.g., light source, camera, monitor) can be used for other endoscopic applications including arthroscopy, laparoscopy, cystoscopy, bronchoscopy, and video otoscopy.

Figure 27-1 A gastrointestinal endoscope tower including (top to bottom) monitor, camera processor, light source, and digital capture system.

In addition to the components of the imaging chain, the following equipment will be required for a state-of-the-art gastrointestinal endoscopy program:

Flexible Gastrointestinal Endoscopes

Not all flexible endoscopes are suitable for gastrointestinal endoscopy. The following features of a gastrointestinal endoscope are essential for the successful imaging of the GI tract:

A typical gastrointestinal endoscope consists of three main components: the hand piece, the insertion tube, and the umbilical cord (Fig. 27-2).

Figure 27-2 External anatomy of an Olympus flexible video endoscope.

(Reprinted with permission of Olympus America Inc.)

Endoscope Hand Piece

The hand piece is held in the left hand as shown in Figure 27-3. The index and middle fingers of the left hand control the suction and air/water valves. Fully depressing the suction or air/water valves will activate suction or irrigation (lens cleaning), respectively. Insufflation is activated by simply covering the hole in the top of the air/water valve using either the index or middle finger. The left thumb is used to control one or both deflection control knobs, which cause the bending motion of the insertion tube. The right hand is used to advance the insertion tube and to turn the deflection control knobs when the left thumb cannot easily reach them.

Figure 27-3 Recommended position of video endoscope handle in left hand.

Each of the deflection control knobs has a lock mechanism, which will secure the tip deflection in a fixed position. These locks may be useful when a lesion or structure is located and the examiner wishes to fix the deflected tip position for a period of time while performing the examination or recording images. In the author’s experience, most veterinarians rarely use these locks, and it is important to remember not to attempt to deflect the tip while the locks are engaged.

The hand piece also contains the inlet to the instrument channel, which is contiguous with the suction channel. When not in use, the channel inlet is kept closed with an airtight cap, so that air cannot escape or enter under the pressure of insufflation or when applying suction.

Some video endoscope hand pieces also contain buttons to control some of the electronic features such as image capture, white balance, light intensity, freeze frame, picture-in-picture, and electronic zoom.

Endoscope Umbilical Cord

The umbilical cord is the portion of the endoscope that connects to the light source and video processor. The light post and air inlet are inserted into an appropriate light source, which usually contains an integrated air pump for insufflation. Also found in this region are the connectors for a suction pump and the irrigation bottle. A standard suction pump is connected with plastic tubing of appropriate diameter. The irrigation water bottle is an accessory usually supplied by the manufacturer, and it is recommended that only demineralized water be used to prevent the buildup of minerals in the irrigation channel of the endoscope.

The pressure compensation valve found in this part of the endoscope serves two important functions. Before and after every procedure, a simple leakage test should be performed by attaching the manometer provided by the manufacturer (Fig. 27-4) and following factory instructions. Detecting leaks early can minimize costly repairs. The other purpose of the valve is to equalize the pressures between the interior and exterior environment during ethylene oxide gas sterilization or air shipment. The pressure compensation cap should never be left in place when the endoscope is being submerged in fluid, as this will cause fluid to leak into the endoscope.

Figure 27-4 Manometer for testing leakage of the endoscope.

The video cable connection with tight cap pictured in Figure 27-2 is a feature of true video endoscopes, but not fiberscopes (see next section). It is here that a video cable would be attached to connect the endoscope to a video processor.

Endoscope Dimensions

The key dimensions of an endoscope are its working length, outer diameter, and channel size. The preferred working length depends upon patient size. For example, a working length of 140 cm or more may be required to reach the duodenum of some giant breed dogs, whereas that length would be inconvenient and unnecessary in feline only practice. A small outer diameter (less than 8 mm) is most convenient for traversing the pylorus of cats and small dogs, but a large working channel (2.8 mm) is preferred to maximize the size of biopsy and foreign-body retrieval devices. Because of the diversity in body size and species differences, the desired combination of options may not be available in one model. The most versatile gastrointestinal endoscope for general small animal use will be at least 125 cm in length, no more than 9 mm in outer diameter, with a biopsy channel of at least 2.2 mm. Figure 27-5 shows a gastrointestinal endoscope designed for small animal use with these parameters in mind.

Figure 27-5 A small animal gastrointestinal endoscope with 140-cm working length, 7.8-mm diameter, and 2.8-mm channel.

Fiberscopes Versus Video Endoscopes

Before the advent of endoscopic video technology, all flexible endoscopes were dependent upon fiber optics to transmit an image from the tip of the scope to the eyepiece. Thousands of long thin fibers of optical glass are bundled into “coherent image bundles” capable of transmitting images over long distances while curving and bending through tortuous anatomy. Fiberscopes, as they are known, are still very much in use today, especially small-diameter models that are commonly used for respiratory and urinary endoscopy. However, they are most commonly used with a video camera attached to the eyepiece (Fig. 27-6), which enables the endoscopist and other members of the endoscopy team to view an enlarged image on a video monitor.

Figure 27-6 Fiberscope with endoscopic camera attached to the eyepiece.

True video endoscopes were introduced into medical and veterinary practice in the mid-1980s. A video endoscope image is initially sensed by a computer chip (image sensor) in the tip of the endoscope and transmitted electronically to a video processor, and finally onto the viewing monitor. While these endoscopes come at a higher cost, the images are not dependent on fiber technology, consequently they produce images of superior quality. The resolution of fiberoptic images is limited, and they often appear pixelated because of the cladding that surrounds individual glass fibers. Furthermore, it is inevitable that individual fibers in the image bundle will break over time, causing small black spots in the image (Fig. 27-7).

Figure 27-7 Fiberoptic image showing “pixelation” and broken fibers.

What is often referred to as the “chip in the tip” of a video endoscope is either a charge-coupled device (CCD) or complementary metal oxide semiconductor (CMOS) image sensor. Although both technologies were invented in the late 1960s, the CCD became dominant because it offered superior images with the technology available at the time. These days, both types of image sensors offer excellent performance with proper design. There is renewed interest in CMOS image sensors for endoscopes because of improvements in quality, potential cost savings, and the availability of smaller sensors that could be used to manufacture smaller diameter endoscopes.

It is worth noting that both fiberscopes and video endoscopes contain glass fibers extending the entire length of the umbilical cord and insertion tube. The fiber bundles found in both kinds of scopes are called incoherent because the orientation of the fibers is unimportant. Rather than transmitting images, these fiber bundles transmit light from the light source to the distal tip of the endoscope to illuminate the subject.

Accessories and Instruments for Flexible Endoscopes

A variety of instruments and accessories are available for flexible endoscopes, which may be designed for single or multiple usage (Fig. 27-8). Although single-use instruments have the advantage of being new and sharp, the multiuse instruments tend to be more cost-effective over time. A typical veterinary practice should have at least two biopsy forceps, three or more foreign-body graspers, and two or three balloon dilators available for immediate usage (see Chapter 55). Among the most popular styles of foreign-body retrieval instruments used by veterinarians are two-prong graspers, basket retrievers (dislodgers), and snares. Additionally, a cytology brush with protective tube is useful for both gastrointestinal and respiratory sampling. It is critical that only instruments of the appropriate size, style, and specification are used with any given endoscope. Channel damage by inappropriate instrumentation is a common cause of fluid invasion, which can result in costly repairs. Above all, instruments should never be forced through the channel against obvious resistance. If resistance is met while trying to pass an instrument through a deflected tip, it is recommended to straighten the tip, then pass the instrument before repositioning the tip.

Figure 27-8 Flexible instruments for use through the channel of flexible endoscopes.

Light Sources and Pumps

Most endoscopic light sources are either halogen or xenon. Halogen is the economical choice, whereas xenon offers a brighter, whiter light at a higher cost. It is important to realize that wattage alone is not necessarily a good indicator of brightness. The wattage simply refers to how much power is being used, but different light source technologies can provide vastly different amounts of light output using the same number of watts of electricity. For example, a 175-watt xenon light source is typically much brighter than a 175-watt halogen light source. Illumination will also depend on the condition and model of endoscope, as well as the light sensitivity of the camera being used. The best way to determine the adequacy of a given light source is to test the complete system in a patient.

Newer light-emitting diode (LED) light sources are becoming more readily available and offer several distinct advantages, including lower cost, longer lamp life (thousands of hours), and improved energy efficiency.

Light sources designed for gastrointestinal endoscopes typically have an integrated air pump and connector that accommodate both the light post and air inlet of an endoscope (Fig. 27-9). The air pump also provides the pressure for irrigation from the water bottle. In some instances the light source and air pump may be separate units, requiring connection by using a special light source adapter and tubing to connect the light source to the air pump.

Figure 27-9 Endoscope light source with integrated air pump.

A suction pump is also required for gastrointestinal endoscopy. A standard unit available in most veterinary practices is sufficient in most cases. It is attached to the connector found on the distal end of the umbilical cord of the endoscope.

Endoscopic Cameras and Monitors

Video cameras and monitors offer the following distinct advantages:

The basic components of an endoscopic camera system are the processor or “box” and the camera head, which contains an integral cable and connects to the eyepiece of an endoscope (see Fig. 27-6). As camera systems are usually designed to work with specific endoscopes, it is important to consider the compatibility of one with the other before making a purchase. Some camera systems are more versatile than others. The camera head contains a sensor (either CCD or CMOS) similar to the one found in the tip of a video endoscope. A camera head is only necessary, therefore, when using a fiberscope or rigid endoscope with an eyepiece. A video endoscope on the other hand will attach directly to the camera processor (also known as a camera control unit [CCU]) with a cable adapter that is inserted into the same receptacle for a camera head (Fig. 27-10).

Figure 27-10 Video endoscope attached to camera processor (top) and light source (bottom)

Endoscopic cameras are commonly classified as single chip or three chip, and the quality varies widely. Three-chip cameras theoretically provide higher resolution and more accurate color reproduction than single-chip cameras. However, high-quality single-chip video systems currently available may provide excellent image quality suitable for even the most demanding gastroenterologists. High definition (HD) video cameras are a newer technology for the endoscopy industry, fueled by the successes of the consumer electronics industry. It is beyond the scope of this chapter to discuss the intricacies of endoscopic video technology, but the reality is that numerous factors contribute to image quality. The best method of selecting a quality system is to work with a reputable manufacturer who is able to provide a demonstration of various options as well as a warranty. It is also important to take into account the supplier’s ability to service the unit over the period of time for which one expects to use it.

Monitor size and style is a matter of preference, but 13- to 20-inch monitors are most commonly used. Because of their size and weight, flat screen monitors are rapidly replacing the standard cathode ray tube (CRT) monitors of the past. The monitor should have the correct input to accept the highest quality video signal (cable) coming from the camera processor, and be of adequate resolution to take full advantage of the camera’s capabilities.

Capturing Images and Video

One of the most significant advantages to endoscopic video technology is the capability to capture images during a procedure for review at a later time. This can be achieved in a number of ways, from simply printing images on paper during the procedure to capturing digital images and videos with a dedicated archiving system that can store and manage the data for later retrieval (a searchable database). Some systems also have networking capability, including Digital Imaging and Communications in Medicine (DICOM) compatibility, so that the patient information and image data can be transmitted directly to a hospital’s central patient database. Newer digital image capture systems are contained within the same housing as the camera itself, which provides the advantages of space savings and portability (Fig. 27-11).

Figure 27-11 Compact unit for veterinary endoscopy includes camera processor, light source, monitor, and digital capture system all in one housing.

Indications

Regurgitation is the most important clinical sign associated with esophageal disease in the dog and cat. The initial diagnostic plan usually involves survey thoracic radiographs, barium esophagram, or fluoroscopic evaluation. Endoscopy is often utilized after radiographic studies to obtain supplemental diagnostic information or to provide direct therapy. Esophageal endoscopy with biopsy may assist in the diagnosis of esophagitis, granulomas associated with Spirocerca lupi infection, neoplasia, and strictures, as well as to facilitate removal of impacted foreign bodies and stricture dilation.^1–5 A thorough endoscopic examination of the esophagus should also be undertaken whenever gastroduodenoscopy is performed. Chapters 21 and 55 provide more details about the clinical signs related to esophageal disease.

Instrumentation

A flexible endoscope with a working length of at least 100 cm, an outside diameter less than 10 mm, and a 2.8-mm diameter biopsy channel is appropriate for endoscopic examination of the esophagus in most dogs and cats.^6–8 A flexible endoscope should also have four-way distal tip deflection, automatic water–air insufflation, and separate suction pump to evacuate fluid and gas from the gastrointestinal tract. In addition to channel biopsy with a flexible endoscope, rigid biopsy forceps can be passed alongside the endoscope, directly through a rigid endoscope (see the following), or a suction biopsy capsule can be used to obtain samples of the intact esophageal mucosa.

Although not optimal, rigid proctosigmoidoscopes have been used to examine the proximal portions of the esophagus. These instruments are inexpensive and available in a variety of diameters and lengths.^9,10 Rigid biopsy forceps permit sampling of larger pieces of tissue than those obtained with flexible biopsy forceps. Care must be taken during this procedure to grasp only mucosa and submucosa, so as not to perforate the esophageal wall. Rigid endoscopes do have some obvious limitations compared with flexible endoscopies. With rigid endoscopes, the ability to visualize the entire circumference of the esophagus is limited by the rigidity of the scope. Moreover, rigid endoscopes do not have the clarity of mucosal visualization and forceps dexterity associated with flexible endoscopes. Despite these limitations, rigid endoscopes are useful in the removal of foreign bodies lodged in the esophagus.^9,10

Patient Preparation and Restraint

Endoscopic examination of the esophagus requires the withholding of food, but not water, for at least 12 hours prior to the procedure.^6,11 If esophageal dilation or obstruction is present, endoscopy should be delayed until the esophagus is cleared of ingesta, which may require at least a 24-hour fast. Small amounts of fluid or food within the esophagus can be suctioned or lavaged into the stomach. Larger amounts of food impair visualization and increase the risk of aspiration during extubation and anesthetic recovery. Endoscopic examination of the esophagus requires general anesthesia to restrain the patient and protect the endoscope.^6,12,13

Diagnostic Procedures

The patient should be positioned in left lateral recumbency.¹⁴ A mouth speculum should be placed between the left upper and lower canine teeth to protect the endoscope from rubbing along the surface of the teeth, and to protect the endoscope if the patient were to awaken during anesthesia. To facilitate passage of the endoscope, the tongue should be grasped and the head and neck slightly extended by an assistant. The insertion tube of the flexible endoscope is passed over the base of the tongue, through the pharynx dorsal to the endotracheal tube, and into the proximal esophagus. The tip of the endoscope should be deflected slightly downward (ventrally) to follow the normal anatomic bend between the mouth and pharynx. The endoscopic tip usually passes easily through the upper esophageal sphincter during the initial insertion, generally making lubrication of the endoscope unnecessary. The proximal esophagus is best examined at the end of the procedure as the endoscope is withdrawn while air is being insufflated (Fig. 27-12).

Figure 27-12 Pharyngoesophageal junction. Endoscopic image of the pharyngoesophageal junction of a dog. This view is best obtained as the endoscope is being withdrawn and air is insufflated.

The esophageal lumen is usually in a state of collapse and when slightly distended has visible longitudinal folds (Fig. 27-13).^6,11,13,15 Constant air insufflation may be necessary to distend the proximal esophagus to allow visualization of the lumen and safe advancement of the endoscope. The endoscopic tip should be centralized within the esophageal lumen by adjusting the inner and outer control deflection knobs. Only minor tip adjustments are necessary, as the esophagus is a relatively straight tube from proximal to distal. By advancing the endoscope only when the lumen is clearly visible, the endoscopist will reduce the risk of esophageal perforation. The endoscope should be advanced until the tip veers away from the center of the lumen. The control knobs should be adjusted slightly to reposition the tip within the center of the lumen, and the endoscope advanced further along the esophagus. In this manner, the endoscope is slowly advanced through the esophagus and into the stomach. Although the entire esophageal mucosa can be visualized as the endoscope is slowly advanced, biopsy and cytologic samples should not be collected until the endoscope is slowly withdrawn at the end of the procedure. Otherwise, hemorrhage could obscure visualization of the esophagus distal to the biopsy site.

Figure 27-13 Proximal esophagus, dog. Endoscopic image of the proximal esophagus of a dog. The lumen is collapsed and longitudinal folds are visible. Air insufflation will expand the visible lumen and allow the endoscope to be safely advanced while the mucosa is examined.

The normal esophageal mucosa is pale pink, smooth, and glistening. In health, the esophageal lumen is usually devoid of food and fluid. The trachea will indent the distended esophagus, and the tracheal rings should be clearly visible (Fig. 27-14). At the tracheal bifurcation, it is common to see pulsation of the heart and/or aorta. The distal esophageal lumen often remains distended and air insufflation is less necessary. As the esophagus passes through the diaphragm and into the abdomen it may deviate as much as 30° toward the animal’s left side.¹⁵ The gastroesophageal junction is normally closed and often assumes a stellate mucosal pattern (Figs. 27-15, 27-16, and 27-17). A small amount of red gastric mucosa can be seen within the distal esophageal lumen.⁶

Figure 27-14 Tracheal indentation. Endoscopic image of the tracheal indentation of a dog (seen between the 3 to 4 o’clock position). Air is insufflated to distend the esophageal lumen, which is the dark area at the center of the photograph.

Figure 27-15 Distal esophagus, dog. Endoscopic image of the distal esophagus of a dog. The gastroesophageal sphincter is closed and is visible at the center of the image.

Figure 27-16 Gastroesophageal sphincter. Closeup endoscopic image of the gastroesophageal sphincter of a dog. The sphincter is closed and a stellate mucosal pattern is visible.

Figure 27-17 Gastroesophageal sphincter. Closeup endoscopic image of the gastroesophageal sphincter of a dog. The directional change of the esophagus, as it passes through the diaphragm into the stomach, is visible as the center of the sphincter is displaced laterally toward the 3 o’clock position of the distal esophageal lumen.

The normal esophageal mucosa is lined by a stiff stratified squamous epithelium and, because of these properties, it is often difficult to obtain mucosal samples using flexible biopsy forceps. On the other hand, tissue sampling of an intraluminal mass or ulcerated mucosa is relatively easy. To obtain a biopsy sample, the endoscope tip should be placed 1 to 2 cm from the area to be sampled and angled toward the esophageal wall. The biopsy forceps are advanced through the biopsy channel until they are visible through the endoscope. The biopsy forceps are opened by an assistant, and the endoscopist advances the forceps until mucosal contact is made. The forceps should be gently advanced until a slight bowing of the forceps can be seen. The assistant closes the forceps and the endoscopist snaps off the tissue sample by withdrawing the closed forceps into the biopsy channel. A small amount of hemorrhage may appear at the biopsy site. For more difficult biopsies, a rigid forceps can be passed alongside a flexible endoscope, or through an accessory rigid endoscope (see next), or a suction biopsy capsule can be used to obtain mucosal samples. As the endoscope is withdrawn, fluid, mucus, and blood should be aspirated through the biopsy channel. After the examination is completed, the area surrounding the endotracheal tube should be examined and any residual fluid should be aspirated to prevent aspiration during recovery.

When passing a rigid endoscope, the head and neck should be fully extended and the endoscope well lubricated. The endoscopic obturator should be placed inside of the rigid scope to facilitate passage into the proximal esophagus. To view the esophagus, the obturator should then be removed, the viewing lens closed, and air manually insufflated with the bulb to distend the esophagus. The endoscope should be slowly advanced as long as the lumen is clearly visible. To obtain a biopsy sample the endoscope should be placed within 1 cm of the lesion, the viewing lens opened, and rigid forceps passed into the endoscope. The esophageal mucosa should be gently grasped and the forceps moved back and forth within the endoscope. If the grasped tissue moves easily, it is safe to completely close the forceps and excise the sample. If the grasped tissue remains fixed to the esophageal wall, the forceps should be opened and the tissue released as a full-thickness tissue sample may have been grasped.

Besides the obvious length and diameter differences between dogs and cats, there are several other differences encountered when performing esophagoscopy in cats.^15,16 First, transverse folds are normally evident in the distal one-third of the feline esophagus as the muscular layer consists entirely of smooth muscle (Fig. 27-18). Second, it is common to visualize superficial blood vessels throughout the length of the feline esophagus (Fig. 27-19).

Figure 27-18 Distal esophagus, cat. Endoscopic image of the distal esophagus of a cat. The transverse folds associated with smooth muscle in the distal third of the esophagus are visible. Superficial blood vessels can be seen at 1, 5, and 8 o’clock.

Figure 27-19 Distal esophagus, cat. Closeup endoscopic image of the distal esophagus of a cat. Superficial blood vessels are visible throughout the image. The transverse folds are indistinct because of overdistention of the esophagus with air.

Therapeutic Procedures

Esophageal Stricture Balloon Dilation

Esophageal strictures are best managed with mechanical dilation (Fig. 27-20). Dilation may be achieved with balloon dilation catheters or bougienage tubes.^4,17–19 Esophageal tears have been reported with balloon dilation catheters, but the technology is still thought to be relatively safe in applying radial forces to the stricture site. A greater risk of perforation because of shearing forces applied by the instrument has been attributed to the use of bougienage tubes, although one recent report showed outcomes similar to those reported for balloon dilation.²⁰ Table 27-1 outlines the parameters needed for a successful balloon dilation. Multiple redilations at 1- to 2-week intervals may be necessary until the stricture is resolved.^3,4,17,21 Esophageal dilation is best performed with direct observation at the time of endoscopy, but it could be performed with videofluoroscopy.

Figure 27-20 Saline-filled balloon dilation catheter for esophageal dilation.

(Courtesy of Cook-Medical.)

Table 27-1 Strategies for Balloon Dilation Treatment of Esophageal Strictures

Intervention	Rationale	Implementation
Barium swallow	Determine location, length, and number of strictures	Barium suspension—30% weight/volume
General anesthesia	High-pressure esophageal dilation stimulates visceral pain	Inhalant anesthesia—e.g., sevoflurane, isoflurane
Patient positioning	Inspection of esophagus and stomach poststricture dilation	Left lateral recumbency for maximal maneuverability
Endoscopes	Direct observation, balloon placement, postdilation trauma	7.5- to 8.5-mm insertion tube, 2.8-mm biopsy channel
Balloon dilation catheters	Multiple catheter lengths and balloon diameters	8 mm × 8 cm to 18 mm × 8 cm balloon catheters*
Procedure	Repeated balloon dilations to achieve increase in luminal diameter	1 to 3 cycles of balloon inflation and deflation/procedure
Manometry	Monitoring of inflation and deflation pressures	Vacuum to 160 psi pressure gauges
Gastrostomy tube placement	Nutritional maintenance during recovery phase with severe strictures	Low-profile gastrostomy tube systems
Recovery phase	Protect esophageal mucosa, inhibit acid secretion, promote healing	Sucralfate, histamine H2-receptor antagonists
Recurrence/prevention	Most esophageal strictures require 2 to 4 successive balloon dilations	Repeat endoscopy at 13-day intervals as needed

^* Sure-Flex Esophageal Balloon Dilation Catheters, Rigiflex Esophageal Balloon Dilation Catheters

Clinical Indications

Indications for gastroscopy include clinical signs of vomiting, hematemesis, anorexia, nausea, and/or melena. Endoscopically detectable gastric diseases have multiple underlying pathogeneses (Table 27-2). Although gastroscopy is usually performed in animals with chronic signs of gastric disease, it should also be considered in animals with acute vomiting caused by gastric foreign body or gastric ulceration causing hematemesis. Followup gastroscopy may be used to monitor effects of therapy in patients with chronic gastritis or ulcers.² Initial diagnostic testing (e.g., complete blood count, serum chemistry, urinalysis, abdominal imaging) serves to eliminate common metabolic disorders (e.g., renal failure, hepatobiliary disease, hypoadrenocorticism, or feline hyperthyroidism) that might mimic primary gastric disease. Endoscopic examination should only be performed after thorough history, physical examination, and diagnostic testing have failed to identify the cause of clinical abnormalities.

Table 27-2 Gastric Diseases or Interventions That Typically Require Gastroscopy

Endoscopic Instruments

A flexible endoscope having a working length of at least 100 cm, an outer insertion tube diameter of 9 mm or less, and four-way tip deflection is ideal for most gastroscopic examinations. Endoscopes with an accessory channel diameter of greater than 2.2 mm will accommodate larger biopsy forceps and foreign-body retrieval devices. For inexperienced endoscopists and feline practitioners, an outer insertion tube diameter of 7.9 mm or less will permit easier duodenal intubation when performing esophagogastroduodenoscopy. Video endoscopes are the current gold standard for clinical practice as they provide superior optics with higher resolution when compared to conventional fiberoptic endoscopes. Video endoscopes also permit simultaneous viewing of procedures by multiple personnel (advantageous for training or assistance with interventions such as gastric foreign-body retrieval) and image capture options, such as video recording. The obvious disadvantage of the video endoscopic systems is their cost. Fiberoptic endoscopes are less expensive, and are equally useful for performing a detailed gastroscopy with collection of targeted mucosal biopsies by an experienced endoscopist.³

A variety of endoscopic accessories should be on hand for both diagnostic and therapeutic purposes. Multiple biopsy forceps and cytology brushes will be needed for adequate tissue sampling and histologic diagnosis. Both multiple use and “single-use” biopsy forceps are available in a variety of styles for gastroscopic examinations. Similarly, gastric foreign bodies come in all shapes, sizes, and angularities, and will often require specific and sometimes several different types of retrieval instruments to successfully remove the object(s) from the gastric lumen.

Patient Preparation

Dogs and cats requiring gastroscopy should have food withheld for 12 to 18 hours prior to endoscopic examination. This minimizes the amount of residual ingesta in the gastric lumen in most instances. Animals with delayed gastric-emptying disorders may have retained luminal debris, ingesta, or fluids in spite of proper patient preparation. Large-breed dogs (>30 kg bodyweight) undergoing gastroscopy may also have gastric retention of fluids, possibly associated with the stress of hospitalization and handling by strangers. In these instances, careful aspiration of free gastric fluid may still permit adequate visualization of mucosal surfaces for lesion detection and tissue sampling.

Gastroscopy should not be performed for 12 to 24 hours following a barium-contrast study, particularly if gastric retention is suspected. The delay should be sufficient time for gastric emptying of barium to occur and to permit optimal endoscopic viewing of all gastric mucosal regions. Survey abdominal radiography will confirm the presence of retained (gastric) barium if there is a question as to its presence. Suction of liquid barium through the accessory channel should never be performed as residue might adhere to the walls of the biopsy channel.

General anesthesia will be required for gastric endoscopy whether it be for diagnostic or therapeutic purposes. Patients should always be placed in left lateral recumbency as this facilitates passage of the endoscope through the antrum and pylorus. This allows any retained fluid to drain away from these regions into the gastric body and facilitates examination of these structures prior to duodenal intubation. Lastly, a mouth gag or oral speculum should be placed to prevent damage to the endoscope in case the animal should awaken from anesthesia during the procedure.

Performing Gastroscopy

A proper gastroscopic procedure should include direct visual inspection of all areas of the stomach.¹ A working knowledge of the normal gastric mucosal anatomy and anatomic landmarks will help the endoscopist to correctly maneuver the endoscope for viewing the gastric fundus, body (corpus), cardia (retroflexed view), incisura angularis (key anatomic structure), antrum, and the pylorus prior to duodenoscopy. Recognition of the location and appearance of normal gastric landmarks will also help to distinguish morphologic abnormalities of these structures, such as focal ulcers that may occur along the incisura or chronic pyloric mucosal hypertrophy, which might obscure the pyloric orifice.

As the endoscope is advanced along the distal esophagus toward the gastroesophageal sphincter (GES), the endoscopist should note the tone (i.e., open vs. closed) and position of the sphincter orifice. Using gentle forward pressure while insufflating air, the endoscope is directed through the GES and passed with minimum resistance into the gastric lumen. Once the GES is traversed, the endoscope is advanced only a short distance while variable degrees of air are insufflated to gently separate the rugal folds. This allows the endoscopist to achieve spatial orientation within this viscus by visualizing the gastric body (corpus), antrum, and incisura angularis. This “birds-eye” view of the stomach permits a panoramic view of the gastric body and greater curvature of the stomach as the insertion tip is moved laterally in a sweeping fashion using both left and right tip deflections (Fig. 27-21). Care is taken to control insufflation such that moderate separation of the rugal folds occurs without overly distending the stomach. A combination of insufflation and aspiration of air optimizes visualization of individual rugal folds and the mucosa along the greater curvature of the gastric body. Once these structures are adequately visualized, the endoscope is advanced through the proximal stomach toward the antrum until the incisura angularis can be identified (Fig. 27-22). This key anatomic landmark appears as a distinct ridge of tissue that serves to separate the body of the stomach from the antrum. The identification of the angularis also allows the endoscopist to orient themselves to the location of the lesser curvature (to the right) and the greater curvature (to the left) when the animal is in left lateral recumbency.

Figure 27-21 “Bird’s-eye” view of the proximal stomach as the endoscope is advanced through the gastroesophageal sphincter. A, This illustration shows the approximate position of the endoscope. B, Endoscopic appearance of the greater curvature of the stomach in a dog photographed from the position of the endoscope shown in A.

Figure 27-22 Endoscopic appearance of the angularis and antrum in a cat after moderate air insufflation. The antrum is characterized by an absence of rugal folds.

The next endoscopic maneuver performed is the retroversion or J-maneuver, which allows a “head-on” visualization of the angularis and the cardiac and fundic regions of the stomach.¹ This procedure begins as the endoscope tip is positioned at about the level of the angularis or is deflected off the greater curvature proximal to the antrum while the endoscope tip is deflected maximally in an upward direction. With slight forward advancement of the endoscope, the endoscope tip is then rotated laterally until the angularis is visualized “head-on.” This view allows the endoscopist to see both the antrum located below this structure and the air-distended gastric body located above it (Fig. 27-23). This “head-on” view of the angularis may not be possible in cats because of anatomic constraints when manipulating the endoscope. To view the cardia and fundus, the endoscope tip is now rotated 180° and retracted toward the esophagus. The endoscope tip is rotated laterally left and right to closely inspect these areas and to view the endoscope as it passes into the stomach through the cardia (Fig. 27-24). Although these regions of the stomach are less commonly affected by mucosal disease, this procedure is generally performed quickly and can identify foreign bodies or gastric ulcers, especially in dogs. Retroversion is slowly reversed by advancing the endoscope forward until the proximal antral mucosa and angularis return into view.

Figure 27-23 Angularis and retroversion (J-maneuver) in a dog. A, This illustration shows the approximate location of the endoscope. B, Endoscopic appearance of the angularis as viewed “head-on” during the retroversion maneuver. The antral canal is seen at the bottom of the field and the gastric body, fundus, and cardia are viewed at the top. The endoscope is seen in the central background as it enters the esophagus through the gastroesophageal sphincter.

Figure 27-24 Retroversion (J-maneuver) in a dog. Retroflexed view of the endoscope as it passes through the gastroesophageal sphincter.

The antrum is readily identified by the location of the angularis, the absence of rugal folds, and the observation of peristaltic waves of contraction (usually seen in dogs) that propagate down toward the pylorus. In cats, passage of the endoscope past the angularis and into the proximal antrum may result in a temporary “red out” as the endoscope tip abuts against the antral mucosa. Advancing the endoscope forward with the tip deflected in an upward direction results in observation of the antral canal and pylorus. In most dogs the endoscope can easily be passed around the angularis and through the antral canal. The pylorus is easily visualized in most animals. Exceptions include patients with retained ingesta or accumulated fluids within the pyloric canal. In dogs, the pyloric orifice is often located off center and is partially obscured by fold(s) of mucosa (Fig. 27-25). Cats have a pyloric orifice that is more centrally located in the pyloric canal. Passage of the endoscope through the pylorus may be easy or difficult. The key to successful passage is keeping the pylorus in the center of the endoscopic field.¹ The position of the pylorus can change as a consequence of antral contractions or breathing patterns by the animal, necessitating slight directional changes of the endoscope tip as it is advanced toward the pylorus. In many dogs, the endoscope is often passed through the pylorus with relative ease. However, in other patients the endoscopist may find it challenging to intubate the duodenum through a closed or “spastic” pylorus. This situation is further complicated by mucosal “red out” as the endoscope tip contacts the pyloric mucosa. Slow gradual directional changes of the endoscope tip will usually be successful in identifying the pyloric orifice in these instances. Steady forward pressure is then applied to advance the endoscope. Excessive force should never be used. Gentle insufflation and careful repositioning of the endoscope tip while advancing will result in eventual success in traversing the pylorus. Pharmacologic manipulation to decrease pyloric tone and facilitate passage of the endoscope through the pylorus has not proven successful in either dogs or cats.^4,5

Figure 27-25 Distal antrum and pylorus in a dog. A, This illustration shows the approximate position of the endoscope. B, Endoscopic appearance of the closed pylorus within a mucosal fold. Only slight changes in tip deflection are required to pass the endoscope through the pylorus.

Technical Concerns

Gastroscopy can be easily and safely performed in most dogs and cats. Cardiopulmonary complications related to anesthesia or excessive prolonged air insufflation causing gastric distention are uncommon.⁶ If respiratory compromise is noted, the stomach should be rapidly deflated to stabilize the patient. The respiratory rate may increase in patients while advancing the endoscope through the pylorus. Passing the endoscope into the antral canal and pylorus of large dogs (>30 kg body weight) may result in inadvertent retroversion (e.g., looping) of the endoscope in the stomach.¹ This situation may occur when excessive air insufflation causes gastric distention and the endoscopist loses orientation within the cavernous lumen. If loop formation occurs, the endoscopist should retract and reposition the endoscope while suctioning off air until the angulus can be viewed. This procedure allows the endoscopist to regain spatial orientation and once again advance the endoscope forward to the pylorus. Small diameter endoscopes (7.9 mm or less) should be used in cats as they are more maneuverable and permit easier duodenal intubation. Gastric perforation is a potential complication of gastroscopy but is rare.

Normal Endoscopic Appearance

The gastric mucosa is normally smooth, pink, and glistening. The rugae appear as linear folds that are uniform in size, shape, and distensibility. Even small amounts of retained gastric or duodenal secretions may obscure portions of the mucosa. Hair can also occasionally be observed within the gastric lumen of cats. The antrum is delineated by the presence of the incisura angularis and is characterized by a paler pink mucosal appearance and an absence of rugal folds. Antral contractions may be observed during gastroscopy in both dogs and cats. The pylorus is easily identified in most animals and may be open or closed.

Abnormal Endoscopic Appearance

Gross mucosal abnormalities are commonly seen in dogs and cats with gastric disease (Fig. 27-26). Lesions may be focal or diffusely distributed throughout the entire gastric mucosa; consequently, careful inspection of all gastric regions will enhance the likelihood that mucosal abnormalities will be detected. Endoscopic lesions of mucosal friability, granularity, and ulcers or erosions are commonly associated with histopathologic abnormalities.^7–10 Friability describes the ease with which the mucosa bleeds upon contact with the endoscope or biopsy instrument (see Fig. 27-26A). An increase in mucosal texture is termed increased granularity (see Fig. 27-26B). Mucosal ulceration-erosion refers to an endoscopically visible breach in the mucosal surface that is often associated with active hemorrhage. Ulcers are focal defects that extend deeply into the adjacent mucosa and often contain hemorrhage and a fibrinonecrotic center (see Fig. 27-26C). Erosions are discrete, superficial mucosal defects that do not have raised margins or necrotic centers (see Fig. 27-26D). Erythema denotes mucosal redness that can be a pathologic or a physiologic response to altered mucosal blood flow, which, in turn, is associated with anesthesia. Mass lesions may be benign (e.g., antral polyp) or malignant (e.g., tumor) and are not readily differentiated based on appearance alone. The presence of food or large volumes of gastric fluids in a properly prepared patient is suggestive of gastric retention. Gastric nematodes (P. rara) may also be observed along the gastric body of a dog with a history of chronic vomiting. Finally, alterations in the distensibility of the gastric wall suggest submucosal infiltrative disease or extragastric compression.

Figure 27-26 Gross mucosal abnormalities seen with gastric diseases. A, This image shows mucosal friability of the gastric body. B, A severely increased granularity of the gastric rugae. C, A focal ulcer along the angularis. D, Numerous superficial erosions of the mucosa on the rugal folds. Note that all of these abnormal appearances are commonly associated with infiltrative and inflammatory disorders affecting the gastric mucosa.

Gastric Biopsy

Gastroscopy is usually performed to obtain gastric-tissue biopsies. Tissue samples should be obtained during gastroscopy whether or not endoscopic abnormalities can be identified.^1,3 Histopathologic lesions of the stomach may be present in patients with an endoscopically normal gastric mucosa. Several different styles of biopsy forceps should be available, including those with smooth or serrated cups, with or without a central spike (Fig. 27-27).¹¹ Personal preference and operator experience are often the main reasons for selection of specific types of forceps. Serrated cup forceps without a central spike are often preferred because they cause fewer biopsy artifacts. The diameter of the endoscope’s accessory channel will dictate what size forceps may be used. A channel size of 2.8 to 3 mm facilitates the use of large forceps for mucosal biopsy. The advantage of large forceps is the ability to sample larger and more diagnostic tissue samples. However, the use of forceps that can be passed through smaller diameter endoscopes might still yield excellent quality biopsies for diagnostic purposes.¹²

Figure 27-27 A variety of pinch forceps used for acquiring gastric biopsies. The serrated jaw forceps consistently provides the largest tissue samples for histopathologic evaluation and is thus preferred.

If gastric lesions are not obvious, the best biopsy samples are obtained from rugal folds along the gastric body. The rugae are prominent and it is easy to grasp large-size tissue samples for diagnostic evaluation. The biopsy forceps are advanced at a 45° to 90° angle into the rugal folds and six to eight mucosal biopsies are collected. Cytologic specimens obtained with a sheathed cytology brush or cytologies made as imprints directly from tissue samples will complement mucosal histopathology.¹³ Gross abnormalities of mucosal friability or increased granularity may be biopsied directly. Superficial mucosal erosions should be biopsied at the edge of the lesion. Gastric ulcers require that tissue sampling be performed along the rim of the ulcer at the interface of abnormal and normal tissue. Taking biopsies from the ulcer pit is not advised as the diagnostic yield is minimal and there is some risk of perforation during the procedure. Masses should be biopsied deeply to avoid necrotic surface debris and superficial cells, which may confound the diagnosis. If diffuse neoplasia is suspected, multiple biopsy specimens collected from deep within the lamina propria should be obtained from both the normal and abnormal appearing mucosa.