Primary sclerosing cholangitis (PSC) is defined as a chronic, progressive disorder characterized by inflammation and fibrosis of both the intrahepatic and extrahepatic bile ducts, ultimately leading to cholestasis and parenchymal scarring. The hallmark pathological feature is progressive periductal fibrosis that forms concentric, circumferential layers—classically described as “onion‑skin” biliary fibrosis. Because PSC can mimic a variety of secondary causes of biliary stricturing, it remains a diagnosis of exclusion, established only after alternative etiologies of biliary sclerosis have been ruled out, primarily through cholangiographic imaging. As the disease advances, ongoing biliary obstruction and inflammation promote hepatic fibrosis, culminating in secondary biliary cirrhosis and eventual liver failure. At this stage, liver transplantation becomes the only definitive treatment option.