Esophageal disorders

One potential indication of chromoendoscopy in the pediatric esophagus is intestinal metaplasia, i.e., Barrett’s esophagus. If this condition is suspected, the main aim of chromoendoscopy is to help increase the diagnostic yield of endoscopic biopsies. Positive staining with methylene blue could also be used to identify endoscopically invisible intestinal metaplasia of the cardia region which may exist in patients with GERD. However, it is questionable if methylene blue staining should be applied to all patients with long‐standing GERD who undergo upper endoscopy, since intestinal metaplasia can also be found in asymptomatic individuals and the advantage of methylene blue staining over random biopsy is controversial. In adult patients with short‐segment Barrett’s esophagus, the sensitivity of methylene blue staining for the detection of intestinal metaplasia varies from 60% to 98%, but is generally higher than that of random biopsies. Abnormal methylene blue staining can also be helpful in delineating dysplastic or malignant areas for endoscopic treatment such as mucosal resection or photodynamic therapy. If mucosectomy is planned, a minimum amount of methylene blue injected with saline into the underlying submucosa which stain it blue, thereby facilitating an accurate removal of the mucosal lesion.

In patients who have undergone mucosal ablation, chromoendoscopy could also help distinguish the regenerating squamous epithelium from residual Barrett’s mucosa. Lugol’s solution has also been used in follow‐up endoscopic examination of young patients who have been treated for Barrett’s esophagus or dysplasia, in order to promptly detect remnants of unstained Barrett’s epithelium.

Studies in adults have shown that chromoendoscopy with Lugol’s solution is superior to conventional endoscopy for the detection of severe dysplasia and early squamous cell carcinoma of the esophagus. In a Chinese population with a high esophageal cancer rate, chromoendoscopy with Lugol’s solution showed a sensitivity of 62–96% and specificity of 63%. However, esophageal dysplasia and cancer are extremely uncommon in pediatric patients and it should be kept in mind that Lugol’s solution can also stain an inflamed esophageal mucosa, namely reflux esophagitis.

Other staining techniques such as indigo carmine and acetic acid have been proposed in association with magnification endoscopy to detect Barrett’s esophagus and dysplasia. Staining with toluidine blue has been reported to have a very high (98%) sensitivity for Barrett’s esophagus, but cannot distinguish between gastric and intestinal metaplasia.

Although studies in adults have shown promising results, so far there are insufficient data supporting routine use of chromoendoscopy for detecting Barrett’s esophagus and dysplasia in children.

Helicobacter pylori infection and related disorders

To date, there are no clear‐cut indications for the use of chromoendoscopy to detect specific gastric disorders in clinical practice. At least two reactive dyes, however, deserve attention and may prove useful in the near future. Congo red stains acid‐secreting mucosa and has been used in adult patients to detect gastric atrophy, which appears as an area of negative staining on the dark blue/black background of the normal mucosa of the gastric fundus and body. Phenol red turns from yellow to red in the presence of alkaline pH, such as that related to the hydrolysis of urea by urease‐producing H. pylori, and has been used to map the extent of H. pylori colonization in the stomach. Both these staining techniques could, therefore, find an application in pediatric patients with long‐standing or refractory H. pylori infection.

Celiac disease

Gluten‐sensitive enteropathy (celiac disease) usually result in endoscopically visible changes of the duodenal mucosa, including a “mosaic” pattern, loss or indentation (scalloping) of Kerckring’s folds, and a visible vascular pattern. Chromoendoscopy with methylene blue emphasizes the mosaic pattern, although it does not seem to increase the diagnostic yield of endoscopy, at least when performed by experienced gastroenterologists. In one study, indigo carmine scattering combined with magnification endoscopy proved superior to standard endoscopy for the detection of small bowel enteropathy, mainly because it was able to distinguish between total and partial villous atrophy. However, since the diagnosis of celiac disease is established by histology and not by endoscopy, duodenal biopsies should be taken whenever celiac disease is suspected, irrespective of the endoscopic appearance of the duodenal mucosa. Therefore, the major contribution of chromoendoscopy in celiac disease is to allow for better targeting – and consequently some sparing – of duodenal biopsies.

Polyposis syndromes

Chromoendoscopy may be very useful to detect smaller lesions in the duodenum of patients with familial adenomatous polyposis (FAP). Small flat duodenal adenomas may, in fact, go unnoticed during standard endoscopy and even capsule endoscopy, but can be identified as negative‐staining lesions when an absorptive dye such as methylene blue is sprayed onto the mucosa. In colonic polyposis, the main aim of chromoendoscopy is the same as in the duodenum, i.e., to increase the detection rate by facilitating the identification of small flat polyps, especially adenomas. The preferred dye for the detection of colonic polyps is indigo carmine, a contrast stain that pools in areas of mucosal irregularity and often gives a three‐dimensional effect, which is particularly useful for the detection of small protruding lesions. Needless to say, magnification endoscopy and high‐resolution endoscopy can add to the accuracy of the technique. In adult studies, left‐sided or total colonic indigo carmine staining significantly increased the detection rate of small flat or depressed adenomas. Chromoendoscopy can also help distinguish between hyperplastic and adenomatous polyps, as they produce different staining patterns. In a recent multicenter study, more than 90% of colonic polyps were correctly classified according to the staining pattern, and for adenomatous polyposis, the sensitivity and specificity were 82% and the negative predictive value was 88%.

Inflammatory bowel disease

In inflammatory bowel disease (IBD), the greatest potential for chromoendoscopy is the ability to detect dysplasia or cancer early in patients with long‐standing ulcerative colitis. Colonic dysplasia and colitis‐related colon cancer may also, occasionally, be a problem in pediatric patients, as in the case of ulcerative colitis presenting before 10 years of age, especially if associated with sclerosing cholangitis. In a randomized controlled trial on 174 patients with long‐standing ulcerative colitis, total colonic methylene blue staining was clearly superior to conventional surveillance endoscopy with biopsy for the detection of early neoplasia (32 versus 10 overall intraepithelial lesions; 24 versus 8 low‐grade and 24 versus 10 in flat mucosa).

Other indications

In the duodenal bulb, methylene blue spray can help identify areas of gastric metaplasia, which is a marker of inflammation such as that related to H. pylori infection. Methylene blue was also used to identify the minor papilla in patients with pancreas divisum.

Equipment

Special reusable spray catheters such as those used for ERCP (e.g., Olympus PW‐5L1) are preferable. The biopsy channel of all modern pediatric video‐endoscopes allows the passage of such catheters (Figure 17.1). It is also convenient to use a new biopsy channel cap in order to minimize the leakage of dye. Endoscopists and support staff with less experience in chromoendoscopy should be particularly careful, as most dyes can produce a fairly persistent staining of skin and clothing. Depending on the specific indication and need, different types of stains can be used, such as stains that are absorbed by the mucosa (vital stains), stains that produce contrast (reactive stains), and stains for tattooing of the mucosa (Table 17.1).

Methylene blue

Methylene blue is actively absorbed by the intestinal epithelium and does not stain nonabsorptive tissues such as the normal esophageal or gastric mucosa. Optimal staining requires washing of the mucosa with a mucolytic agent such as N‐acetylcysteine prior to spraying a 0.25–0.5% solution of the dye, and subsequent washing with water. The absorptive intestinal epithelium – including metaplastic epithelium as in Barrett’s esophagus – is stained blue, whereas the nonabsorptive epithelium – such as ectopic gastric metaplasia – is delineated as an area of negative staining against a blue‐stained background. The presence of dysplasia or early malignancy within Barrett’s epithelium results in inhomogeneous staining, as a consequence of the differential absorption of methylene blue from cells that are depleted of goblet cells and have less cytoplasm.

Methylene blue is generally considered to be safe. However, it has been reported that, once photosensitized by white light, methylene blue may induce oxidative damage of the DNA and although it does not usually stain the dysplastic intestinal epithelium, there is concern that it may increase the risk of carcinogenesis in patients with Barrett’s esophagus. The parents of patients in whom methylene blue staining is being used should be warned that their child’s urine and stool might temporarily acquire a green‐bluish color.

Lugol’s solution

Lugol’s solution contains iodine, which has a special affinity for the glycogen contained in squamous epithelia. For this reason, it is most commonly used in the esophagus, where the normal squamous epithelium is stained green/brown to dark brown or black. Malignancy, dysplasia, metaplasia or even simple inflammation is associated with glycogen depletion and the affected mucosa will thus appear as an unstained area on a dark stained background. Severe allergic reactions to iodine have been reported, so allergy to iodine should be carefully excluded in patients who are undergoing chromoendoscopy with Lugol’s solution.

Toluidine blue

Toluidine blue is a basic dye that binds to the nuclear DNA of epithelial cells, and can, therefore, be used to identify tissues with an increased DNA synthesis such as malignancy. Toluidine blue staining has mainly been used in endoscopic screening for malignant gastric ulcers and early squamous esophageal cancers in at‐risk populations, such as heavy alcohol drinkers and smokers.

Indigo carmine

Indigo carmine is the most widely used contrast stain, and is especially useful to identify and define the margins of neoplastic lesions. Indigo carmine, in fact, typically pools in areas of mucosal irregularity, which are stained indigo (blue/violet) color. After washing, pits, grooves and edges of the lesion are highlighted and this may produce a three‐dimensional effect, which is particularly useful for the detection of small superficial lesions. Indigo carmine at a concentration of 0.1–0.5% is usually sprayed onto the gut mucosa, but may also be given orally in a capsule. Although mostly utilized to identify small superficial polyps, indigo carmine has been applied in several other conditions such as Barrett’s esophagus, gastric cancer, sprue, and ulcerative colitis.

Congo red

Congo red reacts to an acidic pH by changing from red to dark blue or black. Its major application is the identification and mapping of nonsecretory gastric mucosa such as that of gastric atrophy, intestinal metaplasia and gastric cancer, which will appear red in contrast to blue/black secretory areas. A stimulation of acid production with pentagastrin is therefore necessary before staining.

Phenol red

Phenol red is also a reactive dye, but unlike Congo red it reacts to an alkaline pH by changing from yellow to red. Patients should undergo pretreatment with a proton pump inhibitor and an anticholinergic, plus the local application of a mucolytic. Once 0.1% phenol red and 5% urea have been sprayed onto the gastric mucosa of H. pylori‐infected individuals, the alkalinized mucosa is stained red whereas areas of intestinal metaplasia in the stomach will stain negative.

Acetic acid

Acetic acid is a newcomer to GI chromoendoscopy. Preliminary studies suggest that acetic acid stain may help identify Barrett’s esophagus as well as duodenal atrophy in celiac disease, by delineating the features of the metaplastic or atrophic intestinal epithelium.

India ink

When injected into the mucosa, 1% India ink produces a permanent black staining. India ink can be injected superficially into the mucosa to mark the site where a worrisome polyp has been endoscopically removed, or it can be injected deeper to mark a lesion that has to be removed surgically.

Patient sedation

As the main aim of chromoendoscopy is to allow for the visualization of small and fine features of the gut mucosa, the whole procedure can be rendered completely useless if the patient is restless or agitated. Therefore, unless the patient is fully cooperative – which is the exception rather than the rule in pediatric endoscopy – adequate sedation is mandatory to maintain the patient still throughout the procedure. Conscious sedation with midazolam 0.05–0.01 mg/kg IV may not be sufficient in infants or very anxious children, where deep sedation with propofol or a brief general anesthesia may be necessary.

Preparation of the mucosa

There is no doubt that chromoendoscopy gives better results when the gut mucosa to be examined is cleared of mucus (and blood, bile or food debris, if present). So, whenever possible, the mucosa should be washed prior to staining. A better washing is obtained if forceful pressure is applied with a syringe either through the spray catheter or directly into the biopsy channel. If absorptive dyes such as methylene blue or Lugol’s solution are to be used, the mucosa should be washed with a few mL of 10% N‐acetylcysteine to adequately remove mucus. Once the tissue has been stained, a wash with water or saline can remove the excess, nonabsorbed dye. If the vision is disturbed by bubbles or foam, a small volume of an antifoam preparation (e.g., simethicone 10–20 drops) can be added to the wash. A spasmolytic drug such as hyoscine N‐butylbromide can be administered IV to reduce peristalsis or smooth muscle spasm and maximize visualization of the mucosal area of interest. As mentioned above, when a pH‐sensitive dye is used, acid secretion should be either stimulated or suppressed, depending on the dye being used.

Staining technique

The technique for staining is fairly simple. Once the gut area of interest has been reached and adequately washed (see above), the endoscope and the tip of the catheter should be directed towards the mucosa with a combination of clockwise and counterclockwise rotation movements, and the dye should be sprayed onto the mucosa while the tip of the endoscope is gently and slowly withdrawn. The only exception is India ink staining which is, in fact, a permanent tattoo of the mucosa and as such requires injection into the mucosa or submucosa. Once satisfactory images are obtained, it is always advisable to take photographs of the stained mucosa, in order to compare staining features with the histological abnormalities, to assess interobserver variability and also to monitor the improvement of the staining technique over time. Recently, guidelines have been proposed for optimal chromoendoscopy in ulcerative colitis (Table 17.2), but most of these guidelines do apply to chromoendoscopy in general.

Barrett’s esophagus and related disorders

Methylene blue is absorbed by the intestinal epithelium, so it has been used for the endoscopic detection of the intestinal metaplasia typical of Barrett’s esophagus, especially when the diagnosis is uncertain, as it may be in short‐segment Barrett’s. The staining is usually homogeneous but in short‐segment Barrett’s it may be somewhat patchy due to the presence of nonintestinal columnar cells. More importantly, in Barrett’s esophagus, the pattern of methylene blue staining is irregular and heterogeneous if dysplasia or cancer is present (Figure 17.2). Heterogeneously stained or light blue/unstained areas should be biopsied with particular care in search of high‐grade dysplasia and early adenocarcinoma. If Lugol’s solution is used, Barrett’s epithelium, dysplasia or carcinoma will appear as areas of negative staining on the dark green/brown stained background of the normal squamous epithelium.

Helicobacter pylori infection and related disorders

In patients with long‐lasting H. pylori infection, chromoendoscopy with Congo red will demonstrate gastric atrophy as an area of negative staining on the dark blue/black background of the normal mucosa of the gastric fundus and body. Chromoendoscopy with phenol red will define the extent of H. pylori colonization in the stomach by producing a yellow staining throughout the affected gastric mucosa, which is alkalinized by urease.