Background:Histological segmental distribution of ulcerative colitis (UC) may represent an early finding of newly diagnosed UC, especially in pediatric patients; a sign of Crohn's disease; or a predictor of refractory UC. However, its significance remains unknown. This study was performed to compare the final pathologic findings in resected total colon and rectum specimens between pediatric and adult patients with refractory UC who underwent proctocolectomy and clarify the significance of segmental distribution in pediatric patients with UC.Methods:Ninety patients with medically refractory UC (14 with childhood-onset UC and 76 with adult-onset UC) who underwent a two-staged operation comprising total proctocolectomy and ileal J-pouch anal anastomosis in the first stage were included in this study. We retrospectively reviewed all patients' medical records and performed a histological evaluation of the resected total colon using Geboes' grading system for histological inflammation activity of UC and factors of Tanaka's criteria for refractory UC.Results:Histological segmental distribution was more frequently observed in the resected colon at surgery in pediatric (64%) than in adult patients (21%) with refractory UC. The administration of immunomodulators or anti-TNF- antibody within 30 days before surgery was more frequently performed in adults than in children. Patients with refractory UC with a segmental distribution had a statistically significant relationship with shorter duration before surgery (P = 0.0009), male gender (P = 0.0342), and higher activity of disease inflammation in rectum (P = 0.0399). Multivariate analysis revealed the statistically significant relationship between segmental distribution and disease duration before surgery 6 years (P = 0.0031).Conclusions:Endoscopists should perform biopsies of both normal and abnormal mucosa throughout the total colon and follow changes in the pathological pattern because segmental distribution is an important predictor of prognosis.