Biliary intraepithelial neoplasia

Biliary intraepithelial neoplasia (BilIN) is considered to be a precursor lesion of cholangiocarcinoma, but the frequency at which this transition occurs is unknown. 

Terminology

Before 2005, biliary atypia or biliary dysplasia were terms usually employed to refer to BilIN ⁵. 

Epidemiology

The incidence of BIlIN is unknown, with these lesions usually identified in the resected specimens of cholangiocarcinoma or, less commonly, elective cholecystectomies. 

It has been implicated to be more frequent in chronic biliary diseases such as hepatolithiasis ^2,4. Patients with primary sclerosing cholangitis have a high risk of developing BilIN ². 

Pathology

The concept of BilIN as a multistep cholangiocarcinogenesis has been proposed as the biliary counterpart for the pancreatic intraepithelial neoplasia (PanIN) ^1,3. 

Macroscopic appearance

BilINs are usually not visible on gross pathology specimens, eventually characterized as a subtle granularity of the mucosa ¹. 

Microscopic appearance

These tumors show cellular atypia in the form of micropapillary projections into the bile ducts lumen (dysplastic epithelium). They are commonly identified within the mucosa adjacent to cholangiocarcinoma ^1,2. Based on the architectural atypia, they are classified as ^1,5: 

• grade 1 BilIN: representing the low-grade lesions
• grade 2 BilIN: representing the intermediate-grade lesions
• grade 3 BilIN: representing the high-grade lesions, therefore, carcinoma in situ

Radiographic features

Biliary intraepithelial neoplasia is not detected on imaging.