System used to describe staging of primary sclerosing cholangitis. Stage 1 (portal stage)-inflammation, ductal proliferation, and portal edema; stage 2 (periportal stage)-periportal fibrosis with variable ductular proliferation and piecemeal necrosis; stage 3 (septal stage)-septal fibrosis present; stage 4 (cirrhotic stage)-frank biliary cirrhosis.