False negative and false positive rates in common bile duct brushing cytology, a single center experience.

Aim: In this study we tried to find out the accuracy of biliary tract brushing cytology in our center as the largest referral center in the south of Iran.

Background: Common bile duct brushing cytology has been introduced as the method of choice for the diagnosis of pancreaticobiliary malignancies. However, there have been controversial reports about the sensitivity, specificity and overall accuracy of this method in the English literature.

Methods: During the study period (2012-2016) there has been 166 cases of common bile duct brushing cytology taken during endoscopic retrograde cholangiopancreatography (ERCP). One case has been excluded because of inadequate number of cells in the cytology smear. All the smears have been stained by routine cytologic stains and screened by cytotechnologists and diagnosed by expert cytopathologist. Final diagnosis by biopsy has been considered as the gold standard.

Results: According to the final histologic diagnosis as the gold standard, there were 22 false negative and 7 false positive cases. All of the false positive cases have been suspected cases in the background of primary sclerosing cholangitis. The most common final diagnosis of false negative cytologic diagnoses has been intrahepatic cholangiocarcinoma in which no malignant cell has been identified in the presence of adequate number of normal ductal epithelial cells.

Conclusion: Common bile duct brushing cytology is the method of choice for the diagnosis of pancreaticobiliary tract malignancies; however, having high specificity (90%), the sensitivity is low (56%). Cytologic diagnosis of biliary tract malignancies should be made with caution in the patients with primary sclerosing cholangitis. Also it is important to know that high false negative rate is present in common bile duct brushing cytology especially in the cases of intrahepatic cholangiocarcinoma without extension into extrahepatic ducts.