The endoscopic classification developed in Japan [15] and promoted by international consensus in Paris is analogous for superficial neoplastic lesions of the esophagus, stomach, and colon [1, 11] (see Fig. 4.2a). Diagnostic failure mainly comes from a) misclassification of type 0–IIa versus type 0–Is lesions (which is of minor importance for cancer miss rates) and b) under-detection of type 0–IIc lesions which is a major cause for cancer miss rates, because even small 0–IIc neoplasias show a high rate of progression to invasive cancer [1, 7].

Superficial protruding lesions (0–Ip, Isp, Is) are easily detectable. In the stomach, they comprise hyperplastic polyp (glandular cysts, multiple in chronic type B gastritis, 80–90 %), adenoma (5–10 %, with high risk of malignant foci) or differentiated adenocarcinoma (2–3 %), inflammatory polyps (e.g., eosinophilic granuloma, ~2 %), rarely fundic gland polyps (e.g., in familial adenomatous polyposis), hamartomas (e.g., in juvenile polyposis or Peutz-Jeghers syndrome), or hereditary polyposes (e.g., Cowden syndrome, Cronkhite-Canada syndrome). Protruding submucosal lesions must be evaluated by particle biopsy or EUS-guided fine needle biopsy to distinguish MALT lymphomas and submucosal tumors, e.g., carcinoid, lipoma, gastrointestinal stroma tumor, leiomyoma, and rare other tumors.

In colon, most mucosal lesions are protruding; about two-thirds are adenomas (some with HGIN or early cancer), and one-third are harmless hyperplastic polyps that must not be confused with serrated adenoma [1, 4, 11]. Submucosal tumors (lipoma, carcinoid [mainly in rectum], rare leiomyoma) are covered with normal or inflammatory mucosa and so are hamartomas (Peutz-Jeghers polyp and juvenile polyp) and inflammatory pseudopolyps. The latter predominantly occur in chronic ulcerative colitis (UC) that generally poses a challenge to detect and distinguish neoplasia from inflammatory regenerative alterations.

Flat lesions, i.e., slightly elevated, completely flat, and slightly depressed lesions (IIa, IIb, IIc), are less striking on WLI and deserve continuous attention for changes in color and/or surface structure of the mucosa in the esophagus, stomach, and colon. The majority of early cancers (75–80 %) in squamous and columnar epithelial esophagus and in stomach are flat lesions (IIa, IIb, IIc) [1]. Small early gastric cancers (EGC) typically display reddish type 0–IIc lesions when well differentiated and small pale type 0–IIb lesions, often with intact surface structure, when poorly differentiated. The latter are hard to detect and constitute about 15 % of flat EGC in Japan and a higher fraction (up to 40 %) in Western countries [16].

About 36 % of colonic neoplasias present type 0–IIa flat lesions, and about 2–5 % type 0–IIc depressed lesions [4, 7]. As the tumor progresses in size and sm invasion, flat depressed neoplasia (0–IIc) may gain an elevated hyperplastic rim (types 0–IIc + 0–IIa) and become entirely elevated (types IIa + IIc) or ulcerated (0–III) in case of deeply sm-invasive growth (Fig. 4.2a). Shape and deformation of a lesion during inflation/desufflation of the organ also provide information on invasive growth into muscularis mucosae or deep sm/proper muscle layer (Fig. 4.2b).

Laterally spreading-type neoplasia (LST) (Fig. 4.2c) has been defined by Kudo et al. as flat or elevated neoplastic lesion in the colon of more than 10 mm diameter [7]. These neoplasias (mostly adenomas) are barely distinguishable in color from the surrounding normal mucosa and can be quite flat or low elevated. Chromoendoscopy with indigo carmine is advisable to demonstrate tumor extension. Uraoka et al. characterized the spectrum of LST, including nongranular-type LST with high probability of malignant foci (up to 50 %) [17]. The risk of malignancy in granular-type LST is often considered low (<5 %), justifying piecemeal resection, but has also been observed as high as 25 % [17, 18].

The importance of magnification for analysis of surface structure has been established in the colon [7], esophagus [19], and stomach [20]. High-definition (HD) endoscopes, even with the color CCD system, have a physical magnification up to 2 mm distance from the epithelial surface yielding an optical magnification of at least 45-fold. In combination with the 1.5 times digital zoom, these endoscopes offer at least 65-fold magnification (e.g., Exera II or Lucera, OLYMPUS). There are zoom endoscopes with adjustable image magnification up to 120-fold and depth of field (DoF) of 2–3 mm in both the sequential RGB and the simultaneous color CCD system. Moving the endoscope closer than 2 mm to or further than 3 mm from the tissue causes the image to go out of focus. Therefore, the use of a distal attachment on the zoom endoscope is essential to keep precise distance from the lens for clear, focused images (Fig. 4.3). With the dual-focus endoscopes (e.g., Exera III or Lucera Elite, OLYMPUS), the user can switch between standard mode and near mode for close focus observation (with wider DoF 2–6 mm).

Illumination of the mucosa with spectral light from band filters in the light source (narrow-band imaging NBI, Olympus) or computer-based filtering for spectral light bands in the image processor (e.g., FICE, Fujinon, or i-Scan, Pentax), as well as CE, augments the contrast and enhances visibility of structures (image-enhanced endoscopy, IEE) while changing the image color [8, 21–24]. NBI shows hemoglobin absorbance and thus presents images of the microvascular pattern in the superficial mucosal layer (lamina propria) and submucosal vessels. It is based on light filtering for dual narrow-band illumination. From the broadband white light of the xenon lamp, two bands are split with wavelength of 415 and 540 nm that illuminate the surface of the mucosa. The 415 nm blue light band improves the imaging of capillaries (showing up in brown) in the lamina propria (LPM), and the 540 nm green band focuses on small vessels in submucosa (in cyan) allowing to characterize the microvascular pattern (MVP) in normal and neoplastic mucosa [8] (Fig. 4.4). Image processor settings – fine-tuning of enhancement of lines, contrasting of outlines, and color tone – are essential for image quality of magnifying IEE using NBI [9, 10]. The Fujinon intelligent color enhancement system (FICE, Fujinon) is a computer-based system for enhancement of spectral light bands in the image processor. FICE yields IEE of mucosal surface structure and vascular pattern comparable to NBI [23]. The post-imaging digital filter technique (i-Scan, Pentax) is tuned for enhancement of surface structure (SE mode) or red-green-blue spectral bands for “tone enhancement” (TE mode) [21]. FICE and i-Scan use diagnostic principles established for NBI, and key findings reported for NBI also apply [8, 21–24].

Adenomas in gastrointestinal tract are defined on histology by cylinder epithelial cells with enhanced proliferation, even structure of pseudoglands, and noninvasive growth pattern (Fig. 4.6a, b). These clonal epithelial neoplasms form different macroscopic types, e.g., flat types 0–IIb and 0–IIc or flat protruding types 0–IIa that can also grow to sessile or polypoid adenoma or expansively spread out to larger-size, flat or flat-elevated, laterally spreading-type neoplasias (LST, in colon).