Diagnostic pitfalls and the value of fluorescence in situ hybridization as an adjunct to cytologic evaluation of bile duct brushings in patients with primary sclerosing cholangitis.

Background: Primary sclerosing cholangitis (PSC) can present diagnostic difficulties on bile duct brushings as cytologic features mimicking adenocarcinoma may exist. This study evaluates the role of fluorescence in-situ hybridization (FISH) as an adjunct to cytologic evaluation.

Methods: From January 1, 2020, through December 31, 2021, 308 bile duct brushings were processed of which 34 (11%) were malignant, 25 (8%) were suspicious, 36 (12%) were atypical, 204 (66%) were negative and 10 (3%) were nondiagnostic. Follow-up biopsies/resections were performed in the 95 cases with diagnostic cytology (atypical/suspicious/malignant) of which 12 (13%) showed primary sclerosing cholangitis and form the basis of this study. Cytologic, histologic and FISH findings are presented and discussed.

Results: Of the 12 bile duct brushings 4 (34%) were positive/suspicious for adenocarcinoma and 8 (66%) showed atypical epithelial cells. FISH was positive in 2/4 positive/suspicious brushings and negative in the remaining 2 brushings. Histologic findings confirmed the FISH results. The cytologic features of the 2 false positive cases overlapped those of adenocarcinoma. Two of the 8 bile duct brushings with atypical epithelial cells were positive/suspicious for adenocarcinoma on FISH analysis; findings confirmed on histologic follow-up. The remaining 8 patients underwent surveillance for the development of adenocarcinoma with repeat bile duct brushings, FISH analysis and biopsies, each of which has been negative to date.

Conclusion: FISH, as an adjunct to the cytologic evaluation of bile duct brushings from patients with PSC, plays a role in improving diagnostic accuracy and serves as a surveillance tool for the potential development of adenocarcinoma.