Pattern-based histologic approach in colitis with chronic architectural damage: GIPAD recommendations

Abstract Histologic evaluation of colonic biopsies in patients with chronic diarrhea or long-standing colitis is frequently performed in the setting of incomplete clinical, endoscopic, or laboratory information. In this context, overlapping morphologic features across different etiologies often lead to nonspecific or misleading diagnoses, such as "chronic colitis," with potential implications for patient management. To improve diagnostic clarity and clinicopathologic communication, the Italian Group of Digestive Disease Pathology (GIPAD) developed a structured, pattern-based histologic approach for the interpretation and reporting of adult colitis with chronic architectural damage, based on multidisciplinary discussion and critical appraisal of the literature. Distinct histologic patterns are described and correlated with relevant differential diagnoses. Major patterns of colitis with chronic architectural damage are identified, and for each pattern, key morphologic features and principal differential diagnoses—including inflammatory bowel disease and other conditions such as drug-related injury, ischemia, infection, diversion colitis, and immune-mediated disorders—are discussed. A pattern-based histologic approach provides a practical framework for reporting colitis with chronic architectural damage. This strategy narrows differential diagnoses, avoids nonspecific terminology, and supports clinical decision-making, while preserving the primacy of integrated clinicopathologic diagnosis when sufficient information is available.