Colorectal Polyp Classification and Risk Stratification

Overview of Paris Classification

The Paris classification should be used as standard nomenclature to describe the surface morphology of colorectal polyps, providing a common language for stratifying advanced pathology risk and informing removal strategy, as recommended by the American Gastroenterological Association 1, 2
The Paris classification divides lesions into three major morphologic categories, including Type 0-I (Polypoid Lesions), Type 0-II (Non-Polypoid Lesions), and Type 0-III (Excavated), with each category having distinct characteristics and implications for patient care 1, 2, 3

Type 0-I lesions are further classified into pedunculated (0-Ip) and sessile (0-Is) lesions, with pedunculated lesions having a stalk and sessile lesions being flat, and each type having different risks and management strategies 1, 3
Type 0-II lesions are classified into superficially elevated (0-IIa), flat (0-IIb), and slightly depressed (0-IIc) lesions, with each type having different risks and management strategies, and depressed lesions carrying the highest malignancy risk 1, 2, 3
The American College of Gastroenterology recommends that depressed (0-IIc) lesions be carefully evaluated due to their high malignancy risk, with overall submucosal invasion risk ranging from 27%-35.9% 1, 2
Flat elevated (0-IIa) lesions have a substantially lower risk of submucosal invasion, ranging from 0.7%-2.4%, and are generally considered to be at lower risk for malignancy 1, 2

For non-pedunculated adenomatous lesions (Paris 0-II and 0-Is) ≥10 mm, surface morphology should also be described as granular or non-granular LST, as recommended by the American Society for Gastrointestinal Endoscopy 1, 2, 4
LST-Granular (LST-G) subtypes include homogeneous even-sized nodules and mixed-sized nodules, with each subtype having different risks and management strategies, and LST-G with homogeneous even-sized nodules having the lowest submucosal invasion risk (<2%) 3
LST-Non-Granular (LST-NG) subtypes include pseudodepressed and flat elevated lesions, with each subtype having different risks and management strategies, and LST-NG pseudodepressed lesions having the highest invasion risk (27.8% for 10-19 mm; 41.4% for 20-29 mm) 3

Photo documentation of all lesions ≥10 mm before removal is strongly recommended, with suggested documentation of post-resection defect, as recommended by the American College of Gastroenterology 1, 2, 4
Endoscopic descriptors must be documented in the procedure report, including location, size in millimeters, and morphology using Paris classification, to ensure accurate diagnosis and management 1, 2, 4
The recommendation to use Paris classification is conditional with low-quality evidence, reflecting the moderate interobserver agreement and limited prospective validation studies, but it remains the standard nomenclature due to lack of superior alternatives and widespread international adoption 1, 2