Prospective study of biliary strictures to determine the predictors of malignancy

BACKGROUND: There have been few prospective studies regarding the investiga tion of biliary strictures, principally because of rapid technological chan ge. The present study was designed to determine the sensitivity of various imaging studies for the detection of biliary strictures. Serum biochemistry and imaging studies were evaluated for their role in distinguishing benign from malignant strictures. METHODS: Thirty-one patients with suspected noncalculus biliary obstruction were enrolled consecutively in the study. A complete biochemical profile, ultrasound, Disida scan and cholangiogram (endoscopic retrograde cholangiop ancreatography [ERCP] or percutaneous cholangiogram) were obtained at study entry. Stricture etiology was determined based on cytology, biopsy and/or clinical follow-up at one year. RESULTS: Twenty-nine of 31 patients had biliary strictures, of which 15 wer e malignant. The mean age of the malignant cohort was 73.9 years versus 53. 9 years in the benign cohort (P<0.001). Statistically significant differenc es between the malignant and be nign groups, respectively, were as follows: alanine transaminase 235.2 versus 66.9 U/L (P=0.004), aspartate transamina se 189.8 versus 84.5 U/L (P=0.011), alkaline phosphatase 840.2 versus 361.1 U/L (P=0.002), bilirubin 317.8 versus 22.1 mu mol/L (P<0.001) and bile aci ds 242.5 versus 73.2 mu mol/L (P=0.001). Threshold analysis using receiver operative characteristic (ROC) curves demonstrated that a bilirubin level o f 75 mu mol/L was most predictive of malignant strictures. Intrahepatic duc t dilation was present in 93% of malignant strictures versus 36% of benign strictures (P=0.002). Common hepatic duct dilation was less discriminatory (malignant 13.5 versus benign 9.6 mm; P=0.11). Ultrasound was highly sensit ive (93%) in the detection of the primary tumour in the bile duct or pancre as, or in the visualization of nodal or liver metastases. In benign disease , ultrasound failed to detect evidence of intrahepatic or extrahepatic bili ary dilation in most cases. Disida scans were not able to distinguish betwe en malignant or benign strictures and could not accurately localize the lev el of obstruction. The sensitivity of Disida scan for the diagnosis of obst ruction was 50%. Cholangiographic characterization of strictures revealed a n equal distribution of smooth (eight of 13) and irregular (five of 13) str ictures in the malignant group. Ten of 13 benign strictures were characteri zed as smooth. Malignant strictures were significantly longer than benign o nes - 30.3 versus 9.2 mm (P=0.001). Threshold analysis using ROC curves sho wed that strictures greater than or equal to 14 mm were predictive of malig nancy (sensitivity 78%, specificity 75%, log odds ratio 11.23). CONCLUSIONS: A serum bilirubin level of 75 mu mol/L or higher, or a strictu re length of greater than 14 mm was highly predictive of malignancy in pati ents with a biliary stricture. Ultrasound was useful in predicting malignan t strictures by detecting either intrahepatic duct dilation or by visualizi ng the tumour (primary or metastases). Strictures with a 'benign' cholangio graphic appearance are frequently malignant. Disida scan did not add addit ional information. ERCP is necessary to diagnose benign strictures, which t end to be less extensive at presentation.