Introduction

This chapter is focused on practical aspects of esophagogastroduodenoscopy (EGD) in children with the goal of facilitating the learning curve of optimal and safe EGD techniques and also a brief description of some rare pathology of the upper GI tract. The detailed review of common disorders of the esophagus, stomach, and duodenum will be discussed in corresponding chapters.

Indications for EGD

Indications for EGD are covered in Chapter 10.

Assembling the equipment and preprocedure check‐up

To ensure proper function of endoscopic equipment during endoscopy, the key elements of the system should be checked prior to the procedure. This begins with turning the system on and establishing a white balance for a proper color scheme, and optimal brightness of the monitor. Proper function of the water delivery system is confirmed by water spurting vigorously from the nostril while pressing and holding down the air‐water valve. If water is not running out at a decent pressure, check the status of the air pump, adjust the pressure level (medium level is optimal), check if the connecting tube from the water container to the endoscope is unclamped, confirm tight connection of the endoscope with the light source and the water container to the endoscope, tighten the cap of the water container and determine if the air‐water valve is properly mounted. Consider sequential replacement of the air‐water valve, water container and the endoscope, if all other options have been exhausted.

Check and adjust the intensity of the suction. If it is inadequate, check the suction system in a stepwise fashion: make sure that the wall‐mounted suction valve is turned on and the suction canister is sealed off, and that the suction cable is tightly connected to the endoscope and the suction canister. If suction is still inadequate, reassemble the suction canister properly. Then, check the suction valve: pull it out for visual inspection, dip it in water and reinsert it back by pressing down into the suction nostril of the control panel until a soft click occurs. Replace the endoscope if all previous steps have failed.

Wipe the lens of the endoscope with an alcohol swab if the image is blurry.

Endoscope handling

The endoscopist holds the control panel of the endoscope in the left slightly extended palm by the fourth and fifth fingers with the connecting tube hanging behind the thumb (Figure 11.1). The index and middle fingers are positioned comfortably above the suction and air‐water valves respectively (Figure 11.2). This allows the endoscopist to use the thumb for rotation of the large up/down (U/D) angulation knob in a clockwise or counterclockwise direction (Figure 11.3). An additional rotation can be achieved by “locking” the angulation knob from above by the middle finger and repositioning the thumb to the adjacent cog from below in a ratchet‐wheel fashion (Figure 11.4).

The thumb can also be used for adjustment of the small right/left (R/L) angulation knob. However, the easiest way to produce lateral deflection of a flexed‐up bending portion of the endoscope is to twist the left forearm in a clockwise or counterclockwise direction. The generated force is then transmitted from the control panel to the shaft of the endoscope and deviates the tip of the endoscope toward the target. The effectiveness of this technique is directly related to the degree of straightening of the working part of the endoscope between the control panel and the biteguard. However, the R/L angulation knob becomes very useful during target biopsy, the U‐turn maneuver, and intubation of the second portion of the duodenum.

The endoscopist uses the right hand to advance, withdraw, and rotate the shaft of the endoscope. In addition, the right hand is in charge of manipulations with biopsy forceps or other accessories.

Preparation for esophageal intubation

A finely executed esophageal intubation is the key to a safe and successful EGD. Therefore, it is difficult to overestimate the importance of all steps involved in preparation to this phase of EGD.

This begins with proper positioning of the patient on the examination trolley. In children, this can usually be achieved only with adequate sedation. The patient should rest on the examination gurney on the left side with the spine supported by a folded pillow, preventing them from rolling back. The head should be in a neutral position or slightly flexed. Excessive flexion of the neck is counterproductive because it increases the angulation of the endoscope on its way from the mouth to the esophageal orifice, requiring additional force to propel the shaft forward. It is usually associated with discomfort and irritability. On the other hand, excessive neck extension propels the endoscope toward the trachea and should also be avoided. Care should be taken to prevent lateral flexion of the neck and a predictable deviation of the bending portion sideways in the mouth and hypopharynx. Keeping the patient in the optimal position during EGD minimizes the risk of aspiration and facilitates proper localization of lesions within the stomach and duodenum and transition of the endoscope through the pylorus and into the distal duodenum.

The other important component of the preparation routine for EGD is straightening the shaft of the endoscope before inserting it into the mouth. This can be achieved by the examiner positioning themselves about a foot away from the gurney and about two feet away from the patient’s head (the suggested distances are the subject of adjustments based on the actual height and length of a stretched right arm of the endoscopist). The straightening of the endoscope will facilitate its alignment with the esophageal axis, a midline navigation toward the esophagus and steering along the stomach and the duodenum.

Lastly, placement of a biteguard is mandatory for all children, except infants without teeth. The biteguard serves three important functions.

• Protection of the endoscope.
  
• Facilitation of proper positioning of the endoscope between the palate and the tongue.
  
• Anchoring of the suction catheter.

A modern biteguard consists of a plastic cylinder with a front hollow bumper and side‐clips with an attached strip of ribbon, preventing it from sliding to the side.

Despite its clever design, close attention should be paid to the position of the biteguard to avoid mechanical damage of the endoscope when the child becomes more awake or agitated. To prevent accidental trauma, both lips should be gently pulled in corresponding directions (up or down), protecting them from entrapment between the teeth and the biteguard.

Techniques of esophageal intubation

Three different techniques can be used for esophageal intubations: direct vision insertion, blind, and finger assisted. The direct vision technique is the method of choice for pediatric upper GI endoscopy with forward‐viewing endoscopes. Before insertion of the scope into the mouth, the proper function of the angulation mechanism is confirmed by corresponding deviation of the tip of the endoscope to the lateral and vertical movements of the angulation knobs. The bending portion is lubricated to the level of 20 cm and curved slightly downward to mark the vertical plane of the endoscope and to align it with the longitudinal axis of the pharynx by synchronous twisting of the control panel and the shaft. Then, the endoscope is passed through the bite block and advanced over the tongue. Direct observation through the biteguard is necessary to insure the correct/midline position of the scope within the mouth before further insertion. This is especially important in infants and toddlers due to the relatively small volume of the oral cavity and easy displacement of the tongue toward the pharynx by the biteguard.

If the tongue is flipped up or sticking out through the biteguard, attempts to insert the endoscope may push it toward the pharynx, increasing the risk of apnea and accidental trauma of the buccal or pharyngeal mucosa, due to lateral displacement of the instrument. A simple solution is to remove the biteguard from the mouth, fit it over and slide it along the shaft. This opens up more room for manipulation within the oral cavity. Once the bending portion is placed over the tongue, the biteguard is fitted back into the mouth.

From this moment on, attention should be switched to the monitor. While looking at the screen, it is worth remembering about the reverse nature of the endoscopic images which could explain the appearance of a relatively pale tongue with its papillae surface on the upper portion of the monitor and palatine raphe at the bottom (Figure 11.5).

These two structures are the landmarks of the midline approach to the pharynx. Gentle advancement of the endoscope along this pathway and bending it down guarantees a smooth transition into the pharynx and avoidance of accidental trauma. The lumen of the oropharynx may vanish briefly. Two structures, the root of the tongue in the upper portion of the screen (Figure 11.6) and the uvula at the bottom, may emerge just before appearance of the pharynx. The distant view of the epiglottis is the sign that the endoscope is in the pharynx. The epiglottis will occupy the upper part of the screen as a crescent‐shaped structure (Figure 11.7). In approaching the epiglottis, the tip of the scope should be brought down toward the posterior wall of the pharynx. Failure to find the epiglottis indicates that the endoscope was advanced too far anteriorly (above the epiglottis), or too close to the crico‐arytenoid cartilage, or was angled laterally. Always follow the rule of thumb: pull the endoscope back until orientation is fully restored. A reappearance of the uvula pointed up from the bottom of the screen, the tonsils or the median raphe of the tongue at the top of the monitor is a sign that the scope is withdrawn too far back. Reposition the shaft along the midline and move it forward and down slowly until the larynx is approached.

The larynx has a triangular shape with the epiglottis above, two small spherical structures of arytenoid cartilage at the bottom, and the aryepiglottic fold on one side (Figure 11.8). The true vocal cords can be occasionally seen as a white/silver reversed letter “V” (Figure 11.9). A close view of the vocal cords is a warning sign of excessive deviation of the endoscope anteriorly. Remember that the esophageal orifice is hiding behind the crico‐arytenoid cartilage, i.e. at the very bottom of the screen. In order to reach it, the tip of the endoscope should be angled downward toward the posterior wall of the pharynx.

Direct midline intubation of the esophagus is practically impossible due to significant resistance generated by the larynx toward the posterior pharyngeal wall. This force will push the endoscope either to the right or left of the larynx (Figure 11.10). If the scope has slipped to the right, rotate the shaft clockwise to about a one‐quarter turn and, vice versa, twist the shaft counterclockwise if the scope slid to the left (Figure 11.11). Advance the shaft forward gently and angle the bending portion up simultaneously. Appearance of the vertical mucosal fold (Figure 11.12) is the sign to switch rotation in the opposite direction to avoid entering the piriform recess.

The final aspect of esophageal intubation could be simple, if the orifice of the cervical esophagus appeared open (a gentle push forward will propel the endoscope into the esophagus), or could be more challenging if the esophageal orifice is obscured by the tight crico‐pharyngeal sphincter. In this case, direct the tip of the endoscope slightly down below the larynx into a narrow space between the larynx and adjacent pharynx, then deflect the bending portion up and advance the scope forward, guided by the diminishing resistance, toward the evolving cervical esophagus (Figure 11.13). In case of persistent resistance or loss of orientation, pull the endoscope back to the level of the crico‐arytenoid cartilage and repeat esophageal intubation from the opposite side of the larynx.

In neonates and infants under general anesthesia, a gentle side‐to‐side wiggling helps to overcome a noticeable resistance within the cervical esophagus created by the endotracheal tube.

During swallowing, the larynx is moving upwards to protect the airways. It is useful to pull the endoscope back, wiggling with the swallow, and advance it quickly forward through the briefly opened esophagus. However, all upper GI endoscopy in children should ideally occur under GA so this should not be an issue. When the tip of the endoscope is submerged between the cricoid cartilage and posterior wall of the pharynx for longer than 10 seconds, it may induce irritability and agitation even in well‐sedated patients. Apnea and/or bradycardia, especially in infants and toddlers, may also occur due to constant pressure on the larynx and irritation of the nearby superior laryngeal nerve. If intubation of the esophagus lasts more than 15 seconds, it is wise to pull the endoscope out until the child regains normal breathing.

Additional signs to abort esophageal intubation are significant resistance to the passage of the endoscope, the presence of light in the lateral neck, and loss of orientation. Again this should not really be an issue for GA – there is no real excuse for unsuccessful esophageal intubation.

Exploration of the esophagus, stomach, and duodenum

Within the esophagus, the endoscope should be advanced strictly under direct observation of the esophageal lumen. A detailed visualization of the cervical esophagus is challenging due to a tonic contraction of the upper esophageal sphincter. An intense air insufflation is necessary to keep the cervical esophagus partially open.

The thoracic portion of the esophagus is normally patent, except for brief peristaltic activity. It makes detailed examination of the entire tubular esophagus quite easy without air insufflation. Distension of the esophagus with air is indicated only in a few situations such as extraluminal compression, foreign bodies, esophageal varices. and severe esophagitis. Intermittent clockwise or counterclockwise rotations of the endoscope help to keep the esophageal lumen fully visible.

The thoracic esophagus is tapered down at the area of the second physiological narrowing created by the left main bronchus. It is always unilateral (Figure 11.14). A bilateral narrowing of the thoracic esophagus is pathological and warrants further work‐up to rule out a double aortic arch or aberrant subclavian artery.

A useful landmark in the distal esophagus is pulsation of the left atrium. The distal esophagus acquires a funnel shape right above the diaphragm (Figure 11.15). It narrows down and deviates to the left, passing through the diaphragmatic notch (third physiological narrowing). The border between the relatively pale esophageal and bright gastric mucosa, the so‐called “Z‐line,” is slightly irregular (Figure 11.16). The location of the Z‐line in relation to the hiatal notch varies. In general, elevation of the Z‐line by 2 cm or more above the diaphragm is abnormal. The most reliable endoscopic marker of a diaphragm notch is a sequential constriction of the esophageal lumen during inspiration following by relaxation of the same segment with expiration. Respiratory excursion of the diaphragm is blunted in a deeply sedated child with shallow breathing, especially during antegrade approach. Location of the diaphragm in relation to the Z‐line becomes more obvious during retrograde observation (U‐turn maneuver).

To follow the natural course of the abdominal portion of the esophagus, the endoscope has to be slowly advanced and rotated counterclockwise with simultaneous elevation of the tip of the instrument. The straightforward approach to the stomach will result in a loss of orientation due to the close proximity of the posterior wall of the cardia or upper body. The stomach is recognized by the folds of the greater curvature between 5 and 7 o’clock as well as a pool of mucus (Figure 11.17). At this point, the endoscope should be rotated clockwise and bent downward until a panoramic view of the gastric body is achieved (Figure 11.18). Four slightly outlined folds between 1 and 3 o’clock highlight the lesser curvature. These folds disappear quickly during insufflation.

It is important to minimize pumping air into the stomach, especially in neonates and infants, who are quite sensitive to gastric distension and may become irritable, start retching and develop respiratory distress or bradycardia.

Exploration of the distal portion of the gastric body is facilitated by an additional clockwise rotation and upward deflection of the tip of the endoscope. The junction between the gastric body and antrum is marked by a prominent incisura angularis from above and loss of folds of the greater curvature from below (Figure 11.19). Further elevation of the tip facilitates transition of the endoscope toward the antrum.

Resistance or loss of orientation warrants pulling back. In some cases, especially in infants and younger children, it is difficult to reach the pylorus just by pushing the endoscope forward. Instead, it is more productive to use a repetitive back and fore movement in combination with clockwise rotation and advancement of the endoscope slightly deeper each time until the pylorus is reached.

A normal pylorus looks like a ring, which disappears during peristalsis. The length of the normal pylorus channel during relaxation is approximately 3–5 mm. For successful intubation of the pylorus, the endoscope should be advanced along the prepyloric folds. The tip has to be bent slightly downward to avoid flipping into a retroflexed (U‐turn) position (Figure 11.20).

If the pylorus is lost during peristalsis, it is useful to either wait until it opens up spontaneously or to pull the endoscope 3–4 cm backward to regain a panoramic view of the prepyloric antrum.

Gentle pressure is usually sufficient to navigate the endoscope through the pylorus. In some cases, attempts to bypass the pylorus will move the endoscope away from the target. In such circumstances, pull the endoscope back into the gastric body, decompress the stomach and approach the pylorus as close as possible following the direction of prepyloric folds. Apply gentle pressure on the gastric wall and direct the tip toward the visible portion of the pyloric ring using the R/L angulation knob simultaneously until the endoscope is fully engaged within the pylorus. Sometimes, it is useful to pull the shaft back slightly to straighten the bending portion of the scope.

Passage of the pylorus is manifest by the disappearance of resistance and change of the mucosal pattern from smooth to villous/velvet type. The endoscopist must be careful to avoid blind trauma of the duodenal bulb due to rapid advancement of the endoscope. The duodenal bulb should be examined carefully before exploration of the second portion of the duodenum. The endoscope has to be pulled back toward the pylorus slowly and deviated to the right to achieve a panoramic view of the duodenal bulb (Figure 11.21).

There is a “blind” zone in the proximal part of the duodenal bulb between the 3 and 6 o’clock positions. Rotating the patient into the prone position facilitates exploration of this area.

The walls of the duodenal bulb are labeled traditionally as the anterior, posterior, lesser, and greater curvatures (Figure 11.22).

Certain corrections in orientation within the duodenal bulb should be made in relation to the stage of the procedure: the antegrade phase is always associated with coiling of the endoscope within the stomach and distortion of normal anatomy. Alternatively, the endoscope is more or less straightened during the retrograde stage of the procedure and the shape of the duodenal bulb regains its normal pattern (Figure 11.23).

Accurate mapping of lesions in the duodenal bulb is important, for example in patients with duodenal ulcers. Ulcers on the posterior wall of the distal portion of the duodenal bulb or the superior duodenal angle are associated with a high risk of severe bleeding due to intense blood supply to the area and close proximity of the pancreas.

The most efficient and safe way to intubate the second and third portions of the duodenum is the so‐called “pull and twist” technique. The order and specific steps of this maneuver depend on the position of the mucosal folds which outline the transitional zone between the distal portion of the duodenal bulb and the superior duodenal angle: vertical versus horizontal (Figures 11.24 and 11.25).

In a “vertical” scenario, exploration of the second portion of the duodenum begins with advancement of the endoscope and positioning it just behind the AC line. The next step is bending the tip of the endoscope up and to the right into the 5 o’clock direction. This will anchor the scope to the superior duodenal angle. The final step is rotation of the shaft clockwise roughly 90° and pulling it back simultaneously until the duodenal lumen becomes clearly visible. If the duodenal folds are visible but the lumen is not, rotate the endoscope counterclockwise about a quarter turn and orient the tip in the 10–11 o’clock direction.

Intubation of the second portion of the duodenum can be challenging in a “horizontal” scenario. In this case, try a technique for a “vertical” scenario first. If unsuccessful, pull the endoscope back to the upper portion of the gastric body, decompress the stomach and intubate the duodenal bulb. Then, position the endoscope in the middle of the duodenal bulb and rotate it counterclockwise. The goal of this maneuver is to untangle the proximal duodenum and “unlock” the superior duodenal angle. Continue counterclockwise rotation and pull the endoscope back simultaneously until the second portion of the duodenum is reached.

In contrast to the majority of pediatric patients, a “pull and twist” technique has a limited role in intubation of the second portion of the duodenum in neonates and infants. Instead, a gentle push of the thin (less than 6 mm) instrument is safe and the preferred method. However, if this scope is unavailable, a regular 9 mm pediatric endoscope can be used but it is more stiff. Attempts to perform a “pull and twist” maneuver usually resuls in displacement of the endoscope back into the stomach. To overcome this obstacle, advance the endoscope toward the superior duodenal angle and move the tip to the right. If resistance is minimal, continue advancement. Rotate the endoscope counterclockwise about 15–20° as soon as the “crescent” of the duodenal lumen becomes visible. Direct the scope toward the lumen using the up/down angulation knob to achieve a panoramic view of the second portion of the duodenum. Advance the endoscope forward until the duodenal lumen begins moving away due to increased resistance and looping of the endoscope in the stomach.

The hallmark of the second portion of the duodenum is the papilla of Vater (Figure 11.26). During the antegrade stage of the procedure, the major papilla is usually found between 9 and 11 o’clock on the medial wall of the second portion of the duodenum. During withdrawal of the endoscope from the distal duodenum, the location of the major papilla is shifted toward the 12 o’clock position.

Detailed images of the papilla of Vater can be obtained with a side‐viewing duodenoscope (Figure 11.27).

The small duodenal papilla is located 3–4 cm proximal to the major one. It can be found in the right upper corner of the lumen between the 1 and 2 o’clock positions. It is a smooth, 4–5 mm structure, which resembles a sessile polyp.

The hallmark of the third portion of the duodenum is the superior mesenteric artery responsible for a prominent pulsation of the right part of the duodenal wall.

The lumen of the fourth portion of the duodenum is narrowed at the level of the ligament of Treitz (Figure 11.28).

The withdrawal phase of upper GI endoscopy is the best for detailed observation of the entire duodenum, stomach, and esophagus. Retrograde inspection of the proximal stomach or the so‐called U‐turn maneuver is the best technique for careful exploration of the gastric cardia and fundus. It is reasonable to perform it at the end of the examination except for children with portal hypertension or acute bleeding from the stomach.

The U‐turn technique consists of the following steps: first, position the tip of the endoscope in the middle of the gastric body and orient it toward the anterior wall in the 10 o’clock direction. Second, bend the tip of the endoscope further up and advance the shaft forward until the incisura angularis appears, separating the gastric body on the left from the antrum on the right part of the screen (Figure 11.29). Third, pull the endoscope back and rotate it clockwise to achieve a close‐up view of the fundus (Figures 11.30 and 11.31).

For a detailed image of the cardia, target biopsy or precise hemostasis, find the grooves between the shallow folds of the lesser curvature during counterclockwise rotation and pull the endoscope back slowly. Recognition of the Z‐line indicates the end of withdrawal (Figure 11.32). This part of the U‐turn maneuver should be performed with caution to avoid accidental impaction of the sharply bent tip of the endoscope in the distal esophagus.

To get away from the cardia, safely push the endoscope forward, rotate it clockwise and return the control knobs to the neutral position. Check and unlock the control knobs if they lock accidentally to avoid blind trauma of the gastric mucosa. Decompress the stomach as much as possible before withdrawal. Careful examination of the esophagus should be carried out at the end of the procedure.

Biopsy technique

Histological and histochemical analysis is crucial for definitive diagnosis of many diseases involving the GI tract, for example reflux or eosinophilic esophagitis, chronic gastritis, celiac disease, and chronic inflammatory bowel disease. Correct interpretation of regular microscopy slides is problematic without adequate tissue samples and virtually impossible without proper mounting of specimens in children with villous atrophy or dysplasia.

It is always feasible to obtain adequate tissue samples, even with small pediatric size biopsy forceps, if the endoscopist is familiar with the appropriate technique. There are three rules of endoscopic biopsy.

• It is not a blind procedure.
  
• The length of the biopsy forceps beyond the tip of the endoscope is in reverse correlation with the precision of the biopsy.
  
• Forceful pushing of the forceps up against the wall is a dangerous and ineffective way to obtain an adequate tissue sample.

The technique of esophageal biopsy is more complicated than either gastric or duodenal mucosal sampling. This is related to the tangential position of the forceps along the esophageal wall and the relatively narrow space within the tubular esophagus.

The proper technique of esophageal biopsy consists of the following steps. First, the endoscope is positioned 1–2 cm above the target. Then, the bending segment of the endoscope is configured into an L‐shape by rotation of the control knobs upwards and to the right. The goal of this maneuver is orientation of the forceps perpendicular to the mucosa. The biopsy forceps should be advanced just enough to be fully open. Finally, suction is applied, forcing mucosa into the biopsy cap before it closes. The protocol of esophageal biopsy sampling for specific diseases will be discussed in the relevant chapters.

The larger volume of the stomach and duodenum makes the biopsy process less complicated, unless the target lesion is located in the gastric cardia or posterior wall of the proximal portion of the duodenal bulb, and the distal segment of the superior duodenal angle.

To obtain an adequate sample from the target lesion, the biopsy forceps should be positioned as much perpendicular to the surface of mucosa as possible. Application of excessive force to the forceps compromises safety, sample volume and quality of the biopsy, and should be avoided. In general, target biopsy for different areas within the stomach requires different approaches. Thus, biopsy of lesions within the gastric cardia and subcardia areas is more accurate during the U‐turn maneuver. Biopsies from the antrum of the stomach are more efficient if taken when the endoscope is partially withdrawn into the distal portion of the gastric body with the tip deflected upwards.

Biopsy from the anterior wall of the duodenal bulb should be taken when the endoscope is positioned just beyond the pylorus. Biopsy from the distal portion of the duodenal bulb requires slightly deeper insertion of the scope.

Biopsy from the second and third portions of the duodenum provides better samples if taken from the edge of duodenal folds with minimal imbedding into the mucosa. A perpendicular orientation of the forceps to the mucosal folds eliminates the need for deep and forceful imbedding of the biopsy cap into the tissue, prevents mucosal trauma and sampling artifacts, and guarantees the best tissue samples.

Proper orientation and mounting of tissue specimens is crucial for correct histological diagnosis of celiac sprue, inflammatory bowel disease, and dysplasia in patients with long‐standing ulcerative colitis, Barrett’s esophagus, and polyps. The proper tissue mounting technique on a fine synthetic mesh adds no more than 3–5 minutes to the endoscopic procedure. The orientation of tissue samples is more precise with a magnifying glass lamp.

Several steps are involved in proper mounting technique.

• Wearing of tight‐fitting gloves free of talcum.
  
• Gentle transferring of a specimen from the open forceps to the index finger with or without the help of a dissecting needle.
  
• Uncurling of a specimen with a light touch of the side of the dissecting needle until the cleavage surface is exposed.
  
• Recognition of the surface area: the mucosal side of the specimen is more reddish and shiny.
  
• Complete uncurling of the specimen with the submucosal side facing up.
  
• Transferring the specimen from the index finger to the mesh, resting on the thumb of the same hand.
  
  
  
  • Touching the supporting mesh with half of the specimen.
    
  • Sweeping the visible part of the specimen to the mesh by placing one side of the dissecting needle between the biopsy specimen and the index finger.
    
  • Moistening the needle with water.
    
  • Pushing the remaining part of the specimen away from the index finger with the side of the needle.
    
  • Placing the mesh with mounted specimen upside down into the fixative solution to prevent it from floating off the supporting mesh.

The labeled bottle with fixative solution should contain no more than 2–3 biopsy specimens from each site of the GI tract.