Histology shows the damage chronic cholangitis produces in the bile ducts and the portal tracts, and it provides a way to stage the disease. It is not needed for the diagnosis of the usual large-duct form, but it is central to recognising small-duct PSC and to research and prognosis.
Histological patterns
The characteristic lesion is an onion-skin appearance: concentric rings of fibrosis laid down around a medium-sized biliary duct. It reflects repeated rounds of injury and repair in the duct wall, and it is the finding most often associated with PSC — although it is found in only about half of the cases. The duct walls become diffusely thickened and fibrotic, and inflammatory cells infiltrate the fibrotic wall.
Two further patterns complete the picture. Fibro-obliterative cholangitis is the complete obliteration of smaller bile ducts by fibrosis; it is the most specific lesion but is present in only 5–10% of cases. Cholangiectasis is thinning and saccular (rounded) dilation of the duct wall, the histological counterpart of the dilated segments seen on cholangiography.
Histological staging
The disease is described in four stages, which follow the spread of inflammation and fibrosis outward from the portal tract:
- Stage I — portal stage. Disease is limited to the portal tract, with inflammation, expansion of the connective tissue and cholangitis. The onion-skin lesion can be found at this stage.
- Stage II — peri-portal stage. The inflammation extends beyond the portal tract, producing interface hepatitis (inflammation at the boundary between the portal tract and the liver lobule) and peri-portal fibrosis.
- Stage III — septal stage. Septa of fibrosis form and bridge from one portal tract to another.
- Stage IV — cirrhotic stage. The process progresses to cirrhosis.