Biliary tract cytology

Sampling methods

Cytologic specimens from biliary tract include brushings, exfoliated bile, and rinse specimens from biliary stents. Brushing specimens may be obtained either by endoscopic retrograde cholangiopancreatography or by percutaneous transhepatic cholangiography, the former being more sensitive than the latter. Rinse specimens may be obtained from a a biliary stent at the time of stent replacement. The brushing specimen is the one with the highest accuracy.

Indications of biliary cytology

The primary indication for biliary cytology is a suspected malignancy in a patient with biliary stricture. However cytology may also be useful for identifying infectious agents, such as acid-fast bacilli and Giardia. Several infections, including fungi and cytomegalovirus, may coexist in immunocompromised patients.

Preneoplastic lesions

Dysplasia may be present in the biliary tract. Dysplastic cells are usually arranged in clusters showing crowding and nuclear overlapping. They show significant nuclear atypia, with increased N/C ratio and chromatin abnormalities, which is however less pronounced than in adenocarcinoma.

Tumors

Strictures of the biliary tract may be caused by adenocarcinomas. Cytologic features of malignant cells include: increased N/C ratio, chromatin clumping, nuclear molding or loss of honeycombing.

Mucinous adenocarcinoma may be difficult to diagnose, however the above features can usually be identified. The tumor cells show abundant mucin. Hyperchromasia is usually absent, but chromatin clearing and clumping are seen.

Papillary neoplasia may also be challenging to diagnose: distinction between papillary adenoma and papillary carcinoma is particularly difficult. Cytology is not able to exclude an adenocarcinoma arising in an apparent adenoma without histologic examination of the entire specimen.

Differential diagnosis

Marked reactive changes may be seen in brushing specimens from the biliary tract of patients with primary sclerosing cholangitis, mimicking a neoplastic process. Moreover, patients with primary sclerosing cholangitis have an increased risk of development of dysplasia and cholangiocarcinoma.
Dysplastic cell groups usually show more crowding than reactive/reparative cells and more pronounced nuclear atypia.