Classification of image-enhanced endoscopy in colon tumors

One-Zoong Kim

doi:10.5946/ce.2024.263

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Review Classification of image-enhanced endoscopy in colon tumors: One-Zoong Kim; Clinical Endoscopy 2025;58(3):337-351.
DOI: https://doi.org/10.5946/ce.2024.263
Published online: May 8, 2025

Department of Internal Medicine, Uijeongbu Eulji Medical Center, Eulji University, Uijeongbu, Korea

Correspondence: One-Zoong Kim Department of Internal Medicine, Uijeongbu Eulji Medical Center, Eulji University School of Medicine, 712 Dongil-ro, Uijeongbu 11759, Korea E-mail: biblian@eulji.ac.kr

Current affiliation: Department of Internal Medicine, CHA Bundang Medical Center, Seongnam, Korea

• Received: September 30, 2024 • Revised: December 12, 2024 • Accepted: December 13, 2024

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (https://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Abstract
INTRODUCTION
HISTOLOGY AND PATHOLOGY OF COLON TUMOR
ENDOSCOPIC CLASSIFICATION OF COLON TUMORS
CLASSIFICATION OF IMAGE-ENHANCED ENDOSCOPY IN COLON TUMOR
CONCLUSIONS
NOTES
REFERENCES

Abstract

Colorectal cancer accounts for 10% of global cancer cases in each year, making accurate evaluation and resection crucial. Imaging-enhanced endoscopy helps differentiate between hyperplastic polyps and adenomas, guiding treatment decisions. Colon tumors are classified into benign (e.g., serrated and adenomatous polyps) and malignant (e.g., adenocarcinomas). The Paris classification categorizes superficial neoplastic lesions by morphology, while laterally spreading tumors are classified by size and growth pattern. Effective classification aids in determining resectability and appropriate interventions for colon tumors, ultimately improving patient outcomes. Image-enhanced endoscopy improves colon tumor diagnosis using various techniques like dye, optical, and electronic methods. Kudo’s pit pattern categorizes lesions based on surface morphology using dye, while Sano, Jikei, and Hiroshima classifications focus on vascular patterns using narrow-band imaging (NBI). The NBI International Colorectal Endoscopic (NICE) classification integrates these methods to identify lesions, especially deep submucosal invasive cancers. The Workgroup Serrated Polyps and Polyposis (WASP) classification targets sessile serrated lesions, and the Japan NBI Expert Team (JNET) classification further refines adenoma categorization with low- and high-grade adenoma. The Colorectal Neoplasia Endoscopic Classification to Choose the Treatment (CONECCT) classification consolidates multiple systems for comprehensive assessment, aiding in treatment decisions and potentially applicable to artificial intelligence for diagnostic validation across imaging modalities like linked color imaging, blue light imaging, or i-scan.
Keywords: Adenomatous polyps; Colonic polyps; Colorectal neoplasms; Endoscopy; Narrow band imaging

INTRODUCTION

Approximately 10% of cancer patients diagnosed worldwide each year have colorectal cancer, making it the second most common cancer in women and the third most common in men.¹ To treat effectively, active efforts are being made to resect detected colon tumors using endoscopy. The need to accurately evaluate the characteristics of lesions through enhanced imaging endoscopy for effective resection of colon tumors is also increasing. Therefore, distinguishing between hyperplastic polyps and adenomas can help determine whether to perform polypectomy or evaluate the likelihood of submucosal invasion in larger suspicious colorectal lesions to inform future treatments, including surgery. Various classifications of image-enhanced endoscopy have been proposed to assist in the decision-making processes. This article aimed to explain how benign and malignant tumors of the colon are described through various classifications and image-enhanced endoscopy classifications based on pathological knowledge of the colon. Additionally, the accuracy of the image-enhanced endoscopy classification for each type of colon tumor is summarized.

HISTOLOGY AND PATHOLOGY OF COLON TUMOR

Histologically, the mucosal layer of the colon contains numerous interspersed elongated tubular crypts (intestinal tubular crypts and crypts of Lieberkühn) that extend downward towards the muscularis mucosa. Beneath the muscularis mucosa lies the submucosa, which consists of dense, irregular connective tissue containing glands and autonomic ganglion cells embedded within it. The muscularis propria is composed of thick smooth muscles. The serosa surrounds the muscularis and consists of loose connective tissue.²

Colon tissue can transform into tumors owing to various factors, leading to pathologically significant findings. Colon tumors are broadly classified into benign and malignant tumors, with those that protrude towards the mucosal surface and are visually identifiable, referred to as polyps.³ Benign tumors can be largely categorized into adenomatous and serrated polyps, with adenomatous polyps being more common and serrated polyps accounting for only 15% to 45% of all colorectal polyps.⁴ Serrated polyps can be further divided into three subtypes: hyperplastic polyps, sessile serrated lesions, and traditional serrated adenomas.

Hyperplastic polyps are histologically characterized by a narrow base and serrations limited to the upper half of the crypts showing straight crypts. Sessile serrated lesions appear flat and neckless, with serrations present throughout the crypt. Traditional serrated adenomas exhibit villous or tubulovillous structures and cellular dysplasia on their surface.⁴

Tubular adenomas are characterized by the proliferation of the dysplastic columnar epithelium, which expands crypts to form tubular structures. The surface comprises dysplastic epithelial glands in the head region, while the base forms a pedunculated polyp of normal tissue.³ Villous adenomas grow leaf-like toward the mucosa. Dysplasia in adenomas refers to the loss of architectural orientation and uniformity among the epithelial cells. Low-grade dysplasia indicates mild abnormalities in cell arrangement and slight atypia (pseudostratified, hyperchromatic, and penicillate nuclei), whereas high-grade dysplasia shows significant abnormalities in cell arrangement and more pronounced atypia (prominent nucleoli and loss of nuclear polarity).⁴

Malignant tumors originating from epithelial cells are classified as carcinomas, and in the colon, these tumors exhibit a glandular pattern and are thus referred to as adenocarcinomas.³ Early colorectal cancer is defined as cancer cells confined to the mucosa or submucosa, regardless of lymph node metastasis. Invasive adenocarcinoma, which invades the submucosa, is characterized by a desmoplastic response surrounding dysplastic cells, small angulated glands, single-cell infiltration, cribriform growth patterns, and solid sheets of cells. Notably, the dysplastic epithelial cells migrated downwards from the surface.⁴

Invasive adenocarcinoma is classified into the following relative categories based on the extent of submucosal (sm) invasion: sm1 (invasion of one-third of the submucosal layer), sm2 (invasion of two-thirds of the submucosal layer), and sm3 (complete invasion). sm1a indicates horizontal invasion of less than one-fourth the length of the tumor portion in the mucosa, sm1b indicates invasion of one-fourth to one-half, and sm1c indicates invasion of more than one-half (Fig. 1).⁵^,⁶ A study conducted in six hospitals in Japan involving 865 cases of submucosal invasive tumors found that tumors with a submucosal depth of less than 1,000 μm had a 0% rate of lymph node metastasis.⁷^,⁸ Therefore, invasive adenocarcinoma is considered endoscopically resectable when the depth of sm invasion is less than 1,000 μm, and is referred to as superficial submucosal invasive cancer. If the depth of sm invasion is 1,000 μm or greater, it is classified as deep submucosal invasive cancer, which typically requires surgical resection. Advanced colorectal cancer is defined as cancer cells invading beyond the muscularis propria.⁹ Advanced colorectal cancer is morphologically classified based on the classification of advanced gastric cancer. The classification of advanced gastric cancer was proposed by Borrmann in 1926¹⁰ and later developed in Japan. Borrmann type I, polypoid; type II, ulcerative; type III, ulceroinfiltrative; and type IV, diffuse infiltrative; type V, unclassified.¹¹

ENDOSCOPIC CLASSIFICATION OF COLON TUMORS

Colon tumors are typically less than 1 cm in size and are described using the Paris classification system. Tumors that exceed this size are categorized as laterally spreading tumors (LST).

Paris endoscopic classification of superficial neoplastic lesions

In 1993, Kudo published a classification system for early-stage cancer.⁵ The classification includes Ip for pedunculated lesions, Ips for subpedunculated lesions, Is for sessile types, IIa for flat elevated types, IIb for flat types, and IIc for depressed types. In 1997, the Japanese classification was published, changing Ips to Isp (semipedunculated).¹² Subsequently, in 2002, an international workshop in Paris involving endoscopists, surgeons, and pathologists led to the establishment of the Paris endoscopic classification of superficial neoplastic lesions. The term “superficial” refers to lesions that invade only the mucosa and submucosa, and to distinguish them from advanced cancers classified as Borrmann type 1 to 4, they were designated as type 0. Among the polypoid lesions, pedunculated lesions were classified as 0-Ip, sessile lesions as 0-Is, elevated non-polypoid lesions as 0-IIa, flat lesions as 0-IIb, depressed lesions as 0-IIc, and excavated lesions as 0-III. To differentiate the height of Is and IIa, a height of 2.5 mm, based on the closed biopsy forceps, was used.¹³ Therefore, the Japanese classification’s Isp is not included. In the second Japanese classification published in 2009, Isp was retained and changed to the subpedunculated type.¹⁴ However, Isp was recently included in the Paris classification (Fig. 2).¹⁵^,¹⁶

LST classification

The term LST was proposed by Kudo and refers to nonpolypoid lesions that grow laterally and are at least 1 cm in size. LSTs can be classified into two categories: LST granular type and LST nongranular type. The granular subtype is further divided into homogeneous and nodular mixed types, whereas the nongranular subtype is categorized into elevated and pseudodepressed types (Fig. 3).¹⁷^,¹⁸

CLASSIFICATION OF IMAGE-ENHANCED ENDOSCOPY IN COLON TUMOR

Image-enhanced endoscopy refers to endoscopic examinations that improve image quality using dye, optical, and/or electronic methods.¹⁹ For instance, using a dye like indigo carmine and then magnifying the observation corresponds to Kudo’s pit pattern.²⁰ Optical methods involve the Olympus dual focus system, which provides 45× magnification (GIF-HQ290; Olympus Corporation),²¹ while electronic methods include high-definition cameras that achieve 30–35× magnification and electronic chromoendoscopy, which selectively uses specific wavelengths.¹⁹

Dye chromoendoscopy uses dyes such as indigo carmine, which are not absorbed by the mucosal glands, to better distinguish morphological changes, lesion boundaries, surface glandular patterns, and sizes of suspicious lesions.²²

Electronic chromoendoscopy includes Olympus narrow-band imaging (NBI), texture and color enhancement imaging (TXI), red dichromatic imaging (RDI), Fujifilm FICE (Fuji intelligent color enhancement or flexible spectral imaging color enhancement), blue light imaging (BLI), linked color imaging (LCI), and the i-scan (PENTAX). NBI enhances observation of tumors by excluding red light from white light and only illuminating with blue and green wavelengths, thus increasing contrast between the tumor and the mucosa.²³ TXI consists of two modes: TXI mode 2 combines brightness adjustment and texture enhancement, brightening dark areas and suppressing local reflections, while TXI mode 1 enhances color contrast.²⁴ RDI uses three narrow-band lights of slightly longer wavelengths—green, yellow, and red—to detect deeper blood vessels or bleeding points.²⁵ FICE similarly minimizes red and green light while enhancing blue light to better detect lesions on the mucosal surface.²⁶ BLI uses short-wavelength blue laser and light-emitting diode light²⁷ to improve visualization of microvessels.²⁸ To enhance the contrast in dark BLI images, LCI by digital processing increases the redness of the tumor mucosa and whitens the background mucosa.²⁹ I-scan employs software to emphasize pixel edges of lesions for surface enhancement, enhances contrast with a focus on blue, and separates red, green, and blue light for various tone enhancements.³⁰ The electronic chromoendoscopy systems of these companies, although differing in specific methods, share a similar principle. They used short-wavelength light to better visualize surface tumors (NBI, BLI) and enhance the brightness of the darkened image (TXI, LCI, i-scan).³¹ Next, we examined the classification of various image-enhanced endoscopy systems that utilize image enhancement technology.

Kudo’s pit pattern

Kudo’s pit pattern classification, introduced in 1996, categorizes lesions into five main types. Types I and II refer to non-neoplastic epithelial tissues and indicate normal, inflammatory, or hyperplastic tissues. Their shapes can be round, star-shaped, or papillary with associated pits. Types III_L, III_s, IV, and V were classified as neoplastic lesions. Types III_L and IV are protruding tumors, with type III_L having a longer or larger arrangement than normal or a shorter, denser arrangement, whereas type IV exhibits a branched or gyrus-like pattern. Types III_s and V represent depressed tumors, with type III_s showing small tubular or round pit shapes, and type V displaying a nonstructural appearance. Type III_L was predominantly adenomatous, with 1,145 of 1,233 cases identified, whereas type IV included 150 adenomas among 269 cases and 72 cancers. Of the 33 cases classified as cancer, 22 were type V, with 11 showing submucosal invasion.²⁰^,³²

Subsequently, Kudo further divided type V into type V_A (amorphous sign) and type V_N (nonstructural pattern), based on the extent of submucosal invasion. Type V_A is characterized by asymmetric pits, irregular pit sizes, and irregularly arranged lines, indicating superficial submucosal invasion (sm1). Type V_A showed SM invasion in 26.5% of cases. Type V_N appeared exfoliated on the surface and presented a completely nonstructural pit pattern, suggesting sm2 or sm3 invasion. After 2001, this classification was updated to include type V_I (irregular) and type V_N (Fig. 4).³³^,³⁴ Fujii et al.³⁵ demonstrated that type VI with a demarcated area indicates submucosal invasion. Types III_L, III_s, IV, and VI without a demarcated area were classified as noninvasive types, whereas type IV with a demarcated area and type V_N were classified as invasive types (Fig. 5).³⁶ The diagnostic accuracy for noninvasive types was 95% for superficial SM and 83% for deep SM.

Sano classification

In 2006, Sano et al.³⁷ classified polyps based on the honeycomb-like arrangement of the mucosal capillary network surrounding the glands. This capillary network is referred to as a meshed capillary vessel. When observed with NBI, if the capillaries are not visible or are faint, they indicate hyperplastic polyps (type I). If the capillaries were clearly visible, slightly thickened, and sparsely distributed, they suggested an adenoma (type II). Type III is characterized by clearly visible capillaries that are thick, irregular in diameter, exhibit a branched appearance, are curtailed, or show irregularity with a dense distribution, indicating cancer. To treat polyp lesions, Sano et al.³⁷ recommended a three-step strategy based on NBI observations: type I should be monitored; type II should undergo endoscopic resection; and for type III, chromoendoscopy should be performed to assess the pit pattern. If the pattern is classified as V_I, endoscopic resection is advised; however, if it is classified as V_N, surgical referral should be considered (three-step strategy).

In 2010, type III tumors were further subdivided based on the presence of submucosal invasion. Type IIIA is characterized by clearly visible microvascular structures, a high density of microvessels, lack of uniformity, and irregularities that may include branching or interrupted patterns. Type IIIB shows a clear demarcation between the normal and cancerous mucosa on the surface (demarcated area), with very few blood vessels or sparse microvascular areas (Fig. 6).³⁸ In a study involving 130 lesions, the diagnostic accuracy of distinguishing superficial sm from deep sm between types IIIA and IIIB was 87.7%.³⁸ Based on these findings and those of Fujii, type II and type IIIA with a demarcated area should undergo endoscopic resection. If the surface pattern remains, chromoendoscopy should be performed for types IIIB and IIIA with a demarcated area. If the pattern is classified as type V_I without a demarcated area, endoscopic resection is recommended; if there is a demarcated area or if it is classified as type V_N, surgical intervention is indicated. If no surface pattern was observed, surgery was performed (modified three-step strategy).²¹

Jikei classification

In 2008, the Jikei classification system was introduced by Jikei University School of Medicine in Tokyo, Japan. Pattern 1 indicates that blood vessels are not visible, whereas pattern 2 shows slightly dilated blood vessels. Pattern 3V describes a villous lesion with dilated vessels arranged in a regular pattern, whereas pattern 3I features dilated vessels in an irregular arrangement. Pattern 4 was characterized by interrupted or sparse vascular patterns (Fig. 7).³⁹ Using this classification, the accuracy of predicting submucosal invasive cancer for type 4 was 90.5%, with a sensitivity of 78.9% and a specificity of 95.9%.⁴⁰

Hiroshima classification

In 2009, Hiroshima University introduced a classification method for observing the vascular patterns using NBI. Type A refers to cases in which the microvessels are not visible or are extremely unclear. Type B describes thin microvessels observed around the pit, where a clear pit can be seen through the nests formed by these microvessels. Type C features irregular microvessels with heterogeneous diameters and distributions (Fig. 8).⁴¹ Type C is further divided into three subtypes. Type C1 consists of irregularly arranged microvessels, with slightly unclear pits observed through them, and a homogeneous distribution of vessel diameter. Type C2 also had an irregular network of microvessels; however, the pits observed were irregular, with a heterogeneous diameter and distribution of the vessels. Type C3 showed no visible pits, thick irregular vascular diameters, heterogeneous distribution, and areas devoid of vessels (Fig. 9).⁴¹ Type A is primarily associated with hyperplastic polyps (80%), type B is associated with 79.7% of adenomas, and type C includes 29.9% with superficial submucosal invasion and 48.5% with deep submucosal invasion. Of these, type C1 has 42.2% with superficial submucosal invasion, type C2 has 54.5% with deep submucosal invasion, and type C3 shows 100% deep submucosal invasion.⁴¹

Showa classification

In 2009, Showa University in Japan published a classification system that utilized NBI. In this classification, the normal mucosa exhibits a honeycomb-like vascular pattern, whereas faint patterns have thin and unclear vessels. Regular vascular network patterns are primarily observed in adenomas, whereas dense vascular patterns are characterized by well-developed and significantly thick vessels. Irregular vascular patterns feature disrupted networks and tortuous vessels, typically with larger-diameter vessels (twice that of surrounding vessels). The sparse vascular patterns indicated a reduced presence of vessels (Fig. 10).³⁹ Among the 617 polyps in the faint category, 30 of 47 were hyperplastic polyps and 17 were adenomas. In the network pattern, 371 of 377 cases were adenomas. For the dense pattern, 127 of 139 were adenomas, whereas for the irregular pattern, 23 of 34 were cancerous, primarily protruding types. In the sparse pattern, 23 of 29 patients had cancer, primarily in the depressed form. Notably, irregular or sparse patterns indicated that 40 of the 63 cases were superficial submucosal invasive cancers.⁶

Narrow-band imaging International Colorectal Endoscopic classification

In 2013, the Narrow-band imaging International Colorectal Endoscopic (NICE) classification was published, which categorizes lesions as follows: type I represents hyperplastic polyps, characterized by a color similar to that of the surrounding normal mucosa or light brown. The vessel pattern was either not observed or showed faint patterns across the lesion, while the surface pattern may exhibit uniformly sized dark or white spots or a homogeneous absence of pattern.³²^,⁴² This appearance is likely due to the histological findings of serrated crypts confined to the upper half of the lesion.⁴³ Type II refers to adenomas, which display a darker brown color than the surrounding normal mucosa. The vessel pattern featured a brown vascular network surrounding the white epithelium of the crypt openings. The mucosa can appear oval, tubular, or branched, which is consistent with the development of dysplastic epithelial crypts. Type III indicates deep submucosal invasive cancer, with a brown or dark brown color compared to the surrounding normal mucosa. Occasionally, areas with unclear borders appear white. The vessel pattern is disrupted or missing, and the mucosal appearance is amorphous and may be absent (Fig. 11).³²^,⁴² These findings are thought to result from dysplastic epithelial cells, which are amorphous surface pattern, migrating deeply from the surface into the submucosa.⁴³ When using this classification, the average accuracy among five endoscopists was 90.0% (85.1%–93.3%), with a sensitivity of 91.8% (86.7%–95.2%), specificity of 88.3% (83.6%–91.6%), positive predictive value of 88.1% (83.3%–91.4%), and negative predictive value of 91.9% (87.0%–95.3%).⁴²

The Workgroup Serrated Polyps and Polyposis classification

In 2016, the Workgroup Serrated Polyps and Polyposis (WASP) classification was introduced in the Netherlands specifically to address the characteristics of nonpedunculated serrated lesions. This classification system differentiates these lesions based on their surface and vascular patterns. If the lesion had a brown color and/or brown vessels, and if the mucosal surface was oval, tubular, or branched, it was classified as type 2. If these features were not present, they were classified as type 1. Among type 1 polyps, if the lesion exhibited two or more of the following characteristics: clouded surface, clear borders, irregular mucosal pattern, and black dots within the crypts, it was identified as a sessile serrated lesion; otherwise, it was considered a hyperplastic polyp. Type 2 polyps were classified as sessile serrated lesions if they exhibited the aforementioned characteristics; otherwise, they were classified as adenomas (Fig. 12).⁴⁴ When nine endoscopists used the WASP classification, the accuracy improved from 63% (54%–86%) to 79% (72%–86%).⁴⁴ The distinctive features of sessile serrated lesions are thought to stem from a more developed serrated architecture, which extends to the bottom of the crypts. This structure allows for more space on the mucosal surface where mucus from the colon can accumulate, giving it a clouded appearance. Additionally, clearer borders and irregular surface patterns resulted from the more pronounced serrated architecture, leading to the visibility of the black dots within the crypts.⁴³

The Japan NBI Expert Team classification

The Japan NBI Expert Team (JNET) classification, reported in 2016, builds on the NICE classification by incorporating magnified endoscopic findings. Type 1 represents hyperplastic polyps or sessile serrated lesions with an invisible vascular pattern and a mucosal pattern consisting of regular dark or white spots similar to the surrounding normal mucosa. The JNET classification allows for a more detailed observation of the mucosal and vascular patterns than the NICE classification, further subdividing adenomas into low-grade dysplastic adenomas and high-grade dysplastic adenomas/superficial submucosal invasive cancers. Low-grade dysplasia (type 2A) features regular vascular patterns (regular caliber, regular meshed/spiral pattern) and regular surface morphologies (tubular, branched, or papillary). High-grade dysplasia and shallow submucosal invasive cancer, as type 2B, present with variable vascular diameters, irregular distribution, and an irregular or obscure surface pattern.³⁹ The mucosal morphology of adenomas is thought to reflect the development of dysplastic epithelial glands, and as the degree of dysplasia increases, the irregularity of the mucosal pattern becomes more pronounced. Additionally, vascular development also increases in hyperplastic polyps, sessile serrated lesions, and adenomas as dysplasia becomes more severe.⁴³ Deep submucosal invasive cancer, such as type 3, may exhibit loose vessel areas and interruptions in thick vessels, with the mucosal surface described as amorphous areas (Fig. 13).³⁹ When using the JNET classification, the ability to differentiate deep submucosal invasive cancer showed an accuracy of 82.3%, sensitivity of 45.4%, specificity of 98.6%, positive predictive value of 93.3%, and negative predictive value of 80.3%.⁴⁵

Colorectal Neoplasia Endoscopic Classification to Choose the Treatment classification

The Colorectal Neoplasia Endoscopic Classification to Choose the Treatment (CONECCT) classification, developed in France in 2019, was created to integrate seven existing classifications and describe five subtypes of colorectal lesions: the Paris classification, LST classification, Kudo’s pit pattern, NICE classification, JNET classification, Sano’s vascular pattern, and the WASP criteria. IH type refers to hyperplastic polyps, visually corresponding to small polyps (≤10 mm) of type IIa, with a color that is clear or similar to the background. The vascular pattern showed few visible vessels and the fine vessels did not follow the contours of the lesions. The crypts were round and white, and the lesions were not removed. The IS type refers to non-pedunculated serrated lesions that appear flat, such as Paris IIa or IIb, with indistinct borders. The color is a variety of yellowish mucosa (appearing red on NBI), and no black spots are present at the base of the crypts. The crypts were dark and round. The IIA type represents adenomas, which are typically rare depressed lesions among the Paris types Ip, Is, or IIa that appear darker than the background. The vascular pattern was regular, following the crypts, had elongated or branched shapes, and sometimes exhibited a cerebriform appearance. R0 or piecemeal resection is recommended for IS and IIA cases. IIC type denotes high-risk adenomas or superficial submucosal invasive cancer, sometimes presenting as micronodules (≥1 cm) on IIc or IIa lesions, or on granular/nongranular LSTs. It appears black, with an irregular vascular pattern and no avascular areas, and maintains crypt integrity without amorphous regions. Treatment involves endoscopic mucosal resection or endoscopic submucosal dissection for R0 resection, particularly for lesions >20 mm. Type III is a deep invasive adenocarcinoma, sometimes resembling type III or IIc, with nodular areas and spontaneous bleeding. The color can vary from heterogeneous dark to clear in amorphous areas. The vascular pattern consisted of irregular, large interrupted vessels or absent vessels (avascular areas). Crypts may be absent, amorphous, destroyed, or irregular (with clear demarcations). This lesion typically requires lymphadenectomy (Fig. 14).⁴⁶ The CONECCT classification demonstrated a sensitivity of 77.8% (52.4%–93.6%) and specificity of 97.9% (94.6%–99.4%) for deep submucosal invasive cancer.⁴⁷

CONCLUSIONS

Kudo’s pit pattern involves observing the pit patterns using chromoendoscopy, whereas the Sano, Jikei, and Hiroshima classifications utilize NBI to classify the microvascular patterns of lesions through electronic chromoendoscopy. The Showa classification categorizes surface and vascular patterns. The NICE classification integrates the Sano, Hiroshima, Showa, and Jikei classifications and employs NBI to differentiate between pit and vascular patterns for identifying deep submucosal invasive cancer. The WASP classification specifically distinguishes sessile serrated lesions, whereas the JNET classification subdivides adenomas into low- and high-grade dysplasia. Finally, the CONECCT classification allowed for the comprehensive assessment of hyperplastic polyps, sessile serrated lesions, high-grade dysplastic adenomas, and the presence of submucosal invasion in suspicious colorectal cancer lesions. There are studies that have applied the NICE classification to i-scan⁴⁸ and research on the classification that differentiates hyperplastic polyps from adenomas using LCI.⁴⁹ However, most of these classifications are based on studies using NBI. Given that other imaging-enhanced endoscopies operate on similar principles, the CONECCT classification can be adapted for use with LCI, BLI, or i-scan (PENTAX) to create a more universal classification system. Recently, artificial intelligence (AI) endoscopy has been developed to assist endoscopists in polyp detection and support diagnosis. When validating the effectiveness of AI endoscopy, a comparison with the accuracy of classification using image-enhanced endoscopy may provide a more objective evaluation. For example, the CONECCT classification can be applied to an AI to validate its diagnostic accuracy.

Conflicts of Interest

The author has no potential conflicts of interest.

Funding

None.

Fig. 1.

Classification of the degree of submucosal invasion. We divided submucosal cancers into sm1, 2, and 3, according to the depth of invasion, and further divided sm1 lesions into 1a, 1b, and 1c, according to the width of invasion. Reused from the article of Wada et al. Gastrointest Endosc 2009;70:522–531, with original copyright holder’s permission.⁶

Fig. 2.

Schematic representation of the Paris classification of polyp morphology. M, mucosal layer; SM, submucosal layer. Adapted from Johnson et al. Can J Surg 2023;66:E491–E498, according to the Creative Commons license.¹⁶

Fig. 3.

Laterally spreading tumor (LST) classification. SMI, submucosal invasion; LST-G, LST granular; LST-NG, LST non-granular; CI, confidence interval. Adapted from Castillo-Regalado and Uchima. World J Gastrointest Endosc 2022;14:113–128, according to the Creative Commons license.¹⁸

Fig. 4.

Kudo and Tsuruta pit pattern classification for colorectal neoplasia. Adapted from Tanaka et al. Dig Endosc 2004;16:S161–S164, with original copyright holder’s permission.³³

Fig. 5.

(A) A highly magnified image showing irregular pits that vary in size. (B) In a low magnification colonoscopic image, the pits do not occupy the entire surface; this pattern defined the non-V lesion in the present study. (C, D) Magnifying pictures. Adapted from Ohta et al. Dig Endosc 2004;16:308–314, with original copyright holder’s permission.³⁶

Fig. 6.

Capillary pattern classification. Adapted from Ikematsu et al. BMC Gastroenterol 2010;10:33, according to the Creative Commons license.³⁸

Fig. 7.

Jikei classification. Adapted from Sano et al. Dig Endosc 2016;28:526–533, with original copyright holder’s permission.³⁹

Fig. 8.

NBI magnification findings of colorectal lesion. Microvessels are not observed or are extremely opaque (type A); fine microvessels are observed around the pits, and clear pits can be observed via the nest of microvessels (type B); microvessels are irregular, and the vessel diameter or distribution is heterogeneous (type C). Reused from the article of Kanao et al. Gastrointest Endosc 2009;69(3 Pt 2):631–636, with original copyright holder’s permission.⁴¹

Fig. 9.

NBI magnification subclassification of type C. Microvessels comprise an irregular network, pits observed via the microvessels are slightly nondistinct, and vessel diameter or distribution is homogeneous (C1); microvessels comprise an irregular network, pits observed via the microvessels are irregular, and vessel diameter or distribution is heterogeneous (between types C1 and C3) (C2); pits via the microvessels are invisible, irregular vessel diameter is thick, or the vessel distribution is heterogeneous, and avascular areas are observed (C3). Reused from the article of Kanao et al. 2009;69(3 Pt 2):631–636, with original copyright holder’s permission.⁴¹

Fig. 10.

Showa classification. Adapted from Sano et al. Dig Endosc 2016;28:526–533, with original copyright holder’s permission.³⁹

Fig. 11.

The NBI international colorectal endoscopic (NICE) classification. ^a)Can be applied using colonoscopes with or without optical (zoom) magnification. ^b)These structures (regular or irregular) may represent the pits and the epithelium of the crypt opening. ^c)Type 2 consists of Vienna classification types 3, 4 and superficial 5 (all adenomas with either low or high grade dysplasia, or with superficial submucosal carcinoma). The presence of high grade dysplasia or superficial submucosal carcinoma may be suggested by an irregular vessel or surface pattern, and is often associated with atypical morphology (e.g., depressed area). Adapted from Hayashi et al. Gastrointest Endosc 2013;78:625–632, with original copyright holder’s permission.⁴²

Fig. 12.

The WASP classification: method for optical diagnosis of hyperplastic polyps, sessile serrated adenomas/polyps and adenomas based on the NICE criteria and the Hazewinkel criteria in a stepwise approach. Reused from the article of IJspeert et al. Gut 2016;65:963–970, with original copyright holder’s permission.⁴⁴

Fig. 13.

The Japan NBI Expert Team (JNET) classification. ^a)If visible, the caliber in the lesion is similar to surrounding normal mucosa. ^b)Micro-vessels are often distributed in a punctate pattern and well-ordered reticular or spiral vessels may not be observed in depressed lesions. ^c)Deep submucosal invasive cancer may be included. Adapted from Sano et al. Dig Endosc 2016;28:526–533, with original copyright holder’s permission.³⁹

Fig. 14.

The Colorectal Neoplasia Endoscopic Classification to Choose the Treatment (CONECCT) table. The words in bold are the ones that require particular attention when analyzing lesions. LST, laterally spreading tumor; NBI, narrow-band imaging; ESD, endoscopic submucosal dissection. Adapted Fabritius et al. Endosc Int Open 2019;7:e1197–e1206, according to the Creative Commons license.⁴⁶

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Classification of image-enhanced endoscopy in colon tumors

Clin Endosc. 2025;58(3):337-351. Published online May 8, 2025

DOI: https://doi.org/10.5946/ce.2024.263

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Classification of image-enhanced endoscopy in colon tumors

Fig. 1. Classification of the degree of submucosal invasion. We divided submucosal cancers into sm1, 2, and 3, according to the depth of invasion, and further divided sm1 lesions into 1a, 1b, and 1c, according to the width of invasion. Reused from the article of Wada et al. Gastrointest Endosc 2009;70:522–531, with original copyright holder’s permission.6

Fig. 2. Schematic representation of the Paris classification of polyp morphology. M, mucosal layer; SM, submucosal layer. Adapted from Johnson et al. Can J Surg 2023;66:E491–E498, according to the Creative Commons license.16

Fig. 3. Laterally spreading tumor (LST) classification. SMI, submucosal invasion; LST-G, LST granular; LST-NG, LST non-granular; CI, confidence interval. Adapted from Castillo-Regalado and Uchima. World J Gastrointest Endosc 2022;14:113–128, according to the Creative Commons license.18

Fig. 4. Kudo and Tsuruta pit pattern classification for colorectal neoplasia. Adapted from Tanaka et al. Dig Endosc 2004;16:S161–S164, with original copyright holder’s permission.33

Fig. 5. (A) A highly magnified image showing irregular pits that vary in size. (B) In a low magnification colonoscopic image, the pits do not occupy the entire surface; this pattern defined the non-V lesion in the present study. (C, D) Magnifying pictures. Adapted from Ohta et al. Dig Endosc 2004;16:308–314, with original copyright holder’s permission.36

Fig. 6. Capillary pattern classification. Adapted from Ikematsu et al. BMC Gastroenterol 2010;10:33, according to the Creative Commons license.38

Fig. 7. Jikei classification. Adapted from Sano et al. Dig Endosc 2016;28:526–533, with original copyright holder’s permission.39

Fig. 8. NBI magnification findings of colorectal lesion. Microvessels are not observed or are extremely opaque (type A); fine microvessels are observed around the pits, and clear pits can be observed via the nest of microvessels (type B); microvessels are irregular, and the vessel diameter or distribution is heterogeneous (type C). Reused from the article of Kanao et al. Gastrointest Endosc 2009;69(3 Pt 2):631–636, with original copyright holder’s permission.41

Fig. 9. NBI magnification subclassification of type C. Microvessels comprise an irregular network, pits observed via the microvessels are slightly nondistinct, and vessel diameter or distribution is homogeneous (C1); microvessels comprise an irregular network, pits observed via the microvessels are irregular, and vessel diameter or distribution is heterogeneous (between types C1 and C3) (C2); pits via the microvessels are invisible, irregular vessel diameter is thick, or the vessel distribution is heterogeneous, and avascular areas are observed (C3). Reused from the article of Kanao et al. 2009;69(3 Pt 2):631–636, with original copyright holder’s permission.41

Fig. 10. Showa classification. Adapted from Sano et al. Dig Endosc 2016;28:526–533, with original copyright holder’s permission.39

Fig. 11. The NBI international colorectal endoscopic (NICE) classification. a)Can be applied using colonoscopes with or without optical (zoom) magnification. b)These structures (regular or irregular) may represent the pits and the epithelium of the crypt opening. c)Type 2 consists of Vienna classification types 3, 4 and superficial 5 (all adenomas with either low or high grade dysplasia, or with superficial submucosal carcinoma). The presence of high grade dysplasia or superficial submucosal carcinoma may be suggested by an irregular vessel or surface pattern, and is often associated with atypical morphology (e.g., depressed area). Adapted from Hayashi et al. Gastrointest Endosc 2013;78:625–632, with original copyright holder’s permission.42

Fig. 12. The WASP classification: method for optical diagnosis of hyperplastic polyps, sessile serrated adenomas/polyps and adenomas based on the NICE criteria and the Hazewinkel criteria in a stepwise approach. Reused from the article of IJspeert et al. Gut 2016;65:963–970, with original copyright holder’s permission.44

Fig. 13. The Japan NBI Expert Team (JNET) classification. a)If visible, the caliber in the lesion is similar to surrounding normal mucosa. b)Micro-vessels are often distributed in a punctate pattern and well-ordered reticular or spiral vessels may not be observed in depressed lesions. c)Deep submucosal invasive cancer may be included. Adapted from Sano et al. Dig Endosc 2016;28:526–533, with original copyright holder’s permission.39

Fig. 14. The Colorectal Neoplasia Endoscopic Classification to Choose the Treatment (CONECCT) table. The words in bold are the ones that require particular attention when analyzing lesions. LST, laterally spreading tumor; NBI, narrow-band imaging; ESD, endoscopic submucosal dissection. Adapted Fabritius et al. Endosc Int Open 2019;7:e1197–e1206, according to the Creative Commons license.46