Epidemiology and Natural History of Perianal Crohn's Disease: A Systematic Review and Meta-Analysis of Population-Based Cohorts.

Approximately 1 in 5 patients with CD develops perianal disease within 10 years of CD diagnosis, including 11.5% who have perianal disease at presentation. Approximately two-thirds of patients require perianal surgery, with a smaller fraction requiring major abdominal surgery.