Advanced Endoscopic Imaging: Polyps and Dysplasia Detection

NICE criterion

Type 1

Type 2

Color

Same or lighter than background

Browner relative to background

Vessels

None or Isolated lacy vessels

Brown vessels surrounding white structures

Surface pattern

Dark or white spots of uniform size, or Homogenous absence of pattern

Oval, tubular, or branched white structures surrounded by brown vessels

Likely pathology

Hyperplastic

Adenoma

Adapted from Hewett, D.G., et al., Validation of a simple classification system for endoscopic diagnosis of small colorectal polyps using narrow-band imaging. Gastroenterology, 2012. 143(3): p. 599–607 e1

Dye-based chromoendoscopy uses dyes that either absorb into the mucosa (vital dye) or remain on the surface of the mucosa (nonvital). The dye can be applied to targeted areas or to the entire colon (pan-chromoendoscopy). The dyes enhance topography of neoplastic lesions or the pit pattern. Kudo et al. showed the endoscopic pit pattern of dye-enhanced lesions correlated to histology [4]. Adenomatous lesions have a gyrus-like pit pattern, while hyperplastic lesions have an asteroid pit pattern.

Most commonly used dyes are indigo carmine and methylene blue , which both have a blue appearance endoscopically. Both are equally effective to distinguish abnormal mucosa. Indigo carmine is a nonvital dye that coats the mucosa and outlines the pit pattern, enhancing the contrast between varying mucosal morphology. It is applied with a concentration of 0.03–0.5% and lasts a few minutes. Because it is not absorbed, it disappears as it becomes diluted throughout the colon. Methylene blue is a vital dye, which actively absorbs into the intestinal epithelial cells (Fig. 14.1). Neoplasia and inflamed mucosa do not absorb the dye, making it appear brighter than normal mucosa. It is applied at a concentration of 0.1%. After application, the dye stains tissue for approximately 1 min and lasts up to 20 min [2]. Both stains have been shown to be safe with no significant side effects. There was concern that methylene blue may cause DNA damage, but no clinically significant DNA injury has been proven [2].

Fig. 14.1

Chromoendoscopy with methylene blue in a patient with ulcerative colitis. (a) Flat lesion with pale appearance was a tubular adenoma by histology. (b) Inflammatory polyp showed the same uptake of dye as surrounding tissue without the typical pale appearance or changes in the pit pattern. © Aquilant Endoscopy Ltd. with permission

Adequate visualization of mucosa with chromoendoscopy requires excellent bowel preparation. Any remaining material in the colon should be aspirated by the endoscopist when advancing through the colon. The dye is applied upon reaching the cecum directly into the accessory channel using a 60-mL syringe or a spray catheter. The dye can also be diluted into 1 L of sterile water and applied by the endoscopist by pressing the foot pedal of the water pump. The dye coverage is improved if the colon is decompressed. For pan-chromoendoscopy, segments of 20–30 cm are sprayed. Immediate inspection can be done with indigo carmine, while methylene blue requires 60 s to absorb. Methylene blue-coated tablets have been reported for the use in chromoendoscopy, with delivery of dye directly to the colon, but more studies will need to be done to determine the efficacy of this dye delivery [5].

In average-risk individuals, dye-based chromoendoscopy, in comparison with white light endoscopy (or high definition (HD) endoscopy) has shown significant benefit in detection of lesions that are commonly missed: diminutive polyps, proximal adenomas, and flat polyps. Adenoma detection rate (ADR) has been studied in chromoendoscopy, in comparison with white light colonoscopy. In comparison with standard white light colonoscopy, or HD colonoscopy, chromoendoscopy showed a small increase in ADR or no effect on ADR. The significant benefit of chromoendoscopy was shown to detect more diminutive polyps per person using dye-based chromoendoscopy [6]. Chromoendoscopy increases detection of more proximal, flat, and serrated lesions. Although this technique can significantly increase detection of the often missed lesions, the main disadvantage of dye-assisted chromocolonoscopy is the length of the procedure.

Patients with Inflammatory Bowel Disease (IBD) are at increased risk for colorectal cancer and require dysplasia surveillance after 8 years of diagnosis. Dye-assisted chromoendoscopy is superior to white light with standard biopsies and improves dysplasia detection by 3- to 4.5-fold [7]. Currently, European guidelines recommend chromocolonoscopy with standard biopsies for dysplasia surveillance in IBD patients. In the USA, chromoendoscopy is used commonly and is the preferred choice for dysplasia screening in IBD patients; however, this is currently not considered standard of care. More studies need to be done prior to establishing chromoendoscopy as the gold standard. Of note, the pit pattern may not be as clear in patients with long-standing inflammation as the background mucosa may appear abnormal. Because dysplasia may not be clear to identify, the American Gastroenterology Association recommends only experienced physicians perform chromoendoscopy.

Digital Chromocolonoscopy

Dyeless or digital chromocolonoscopy uses imaging-enhanced optical techniques. This technique uses optical technology to enhance lesions. Narrow band imaging (NBI) uses optical filters in the light source to enhance superficial and deep vessels (Fig. 14.2). Normally, white light bandwidth has red–green–blue. Hemoglobin absorbs green and blue light. NBI filters the white light to allow blue (415 nm) and green (540 nm) to pass but blocks red wavelengths. Neoplastic lesions in the colon tend to have altered mucosal vessels, which absorb the light, while normal mucosa reflects it. As a result, neoplastic lesions are enhanced under NBI.

Fig. 14.2

Narrow band imaging (NBI) of tubular adenomas of the colon in a single patient. (a) White light and (b) NBI showing a large flat tubular adenoma with polypoid component extending onto the folds. NBI delineates the adenomatous lesion from surrounding normal mucosa and so-called chicken skin mucosa. (c) White light and (d) NBI depicting a flat tubular adenoma. The pit pattern is accentuated by NBI in a lesion that appears subtle under white light

Studies have compared ADR using NBI or white light colonoscopy. NBI improved ADR in comparison with conventional white light colonoscopy but was the same in comparison with HD colonoscopy [8]. The main disadvantage of NBI is the dark color, which limits its use as a screening technique (Fig. 14.3).

Fig. 14.3

NBI of a hyperplastic polyp . (a) White light and (b) NBI show a hyperplastic polyp in the rectum

Another form of digital chromoendoscopy is the iScan (Pentax, Japan), which is a digital filter, which enhances certain wavelength patterns that are absorbed. The software is designed to enhance certain characteristics of the mucosa. Some studies showed that iScan may improve adenoma detection, which were mostly diminutive and hyperplastic.

Fujinon Intelligent Color Enhancement (FICE, Fujinon Inc., Japan) is similar to the iScan. FICE captures the whole white light spectrum. As the light is captured, a computer-based algorithm enhances certain combinations of wavelengths. FICE allows for better visualization of mucosal morphology and enhances vascular and pit patterns, but data showed that it did not improve ADR.

Improvement in Visualization

Several modalities have been developed to improve visualization in the colon. Diminutive polyps have a very low malignancy risk, but three or more predict risk of future colonic adenocarcinoma. The number and size of polyps at the time of the screening colonoscopy determines the subsequent screening intervals. Therefore, not missing polyps is crucial in determining a patient’s future risk and screening intervals. Diminutive polyps are more likely to be missed, especially if located behind folds, where a colonoscope cannot easily visualize the mucosa. Several colonoscope accessories have been created in order to improve visualization.

Cap-Assisted Colonoscopy

Cap-assisted colonoscopy (Fig. 14.4a) is performed with a 4 mm clear plastic cap on the end of the colonoscope. This device is designed to improve mucosal visualization by pulling back folds, where polyps may hide. The cap is also meant to avoid a “red-out” during advancement to the cecum, when maneuvering around flexures. A randomized, prospective trial did not find significance in the adenoma detection rate but had shown an improvement in the cecal intubation rate [9].

Fig. 14.4

Devices that attach to the distal tip of colonoscopes. (a) Endoscopic caps: (1) Hard straight cap. (2) Hard oblique cap. (3) Large caliber soft oblique cap. With permission Sumiyama, K, Rajan E. Endoscopic caps. Tech Gastroinest Endosc 2006; 8(1):28–31 [20]. © 2006 Elsevier Inc. (b) EndoRing^®. (c) Endocuff^®

EndoRing

The EndoRing (EndoAid Ltd., Caesarea, Israel) (Fig. 14.4b) is a circular colonoscope cap device that fits on the end of most colonoscopies. It has 3 layers of clear, soft, and flexible rubber-silicone rings, which help to flatten folds upon withdrawal. The rings are soft and should allow for terminal ileum intubation. This device was studied in a randomized controlled multicenter study, the CLEVER study [10]. The investigators compared tandem colonoscopies: EndoRing-assisted colonoscopy, followed by immediate standard exam, versus a standard colonoscopy followed immediately by EndoRing-assisted colonoscopy. This study (funded by EndoAid) compared adenoma miss rate of the two groups. The group that received the EndoRing-assisted colonoscopy first had a statistically significant lower rate of polyp miss rate (10.4%), compared with 48.3% adenoma miss rate in the group that started with a standard colonoscopy. Of note, the EndoRing-assisted colonoscopies had statistically significant longer procedure time, which may account for the difference in adenoma detection. Overall, this device increased adenoma detection, without significant hindrance to the endoscopist, especially diminutive polyps in the proximal colon, where the majority of polyps are missed.

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