We have reported a prospective study of all patients with newly diagnosed biliary strictures from a single institution over 12 months. Although statistically significant differ­ences were found in most biochemical parameters, ALT and bilirubin best discriminated between malignant and benign strictures. In this series, a serum bilirubin level of 75 pmol/L or greater was highly predictive of a malignant etiology for the stricture (Table 2). This suggests that a more critical nar­rowing exists in the malignant strictures. Furthermore, the stricture length on cholangiography was significantly greater in malignant versus benign strictures (30.3 versus 9.2 mm, P=0.001), suggesting that malignant strictures are more ex­tensive at presentation.

There were important differences in the ultrasound char­acteristics of patients with malignant versus benign stric­tures. Malignant strictures were more likely than benign ones to induce intrahepatic duct dilation (93% versus 36%, P=0.002). The degree of obstruction was not assessed in prior ultrasound series as a discriminator between malignant and benign etiologies. Furthermore, sonographic evi­dence suggestive of malignancy (visualization of primary tu­mour or metastases) was present in 14 of 15 patients. The abdominal ultrasound, therefore, plays an important role both in the estimation of stricture severity as judged by the presence or absence of intrahepatic duct dilation and in the assessment of malignant etiology because tumour can usually be directly visualized. It is relatively insensitive, however, for the diagnosis of benign strictures, many of which are associ­ated with only low grade obstruction. We did not assess the role of CT scanning in this study because ultrasound per­forms as well and is less expensive. Helical CT may have a future role, but further study is required.

Disida nuclear scans are frequently performed in the in­vestigation of a wide variety of biliary tract diseases. In this series, they were insensitive for the diagnosis of benign stric­tures, especially those with low grade obstruction. High grade obstruction was readily detected but the anatomic site could not be localized in most cases. High grade extrahepatic biliary obstruction appears to induce a functional intrahepatic cholestasis, which was the most common finding in this series. This is rapidly reversed with endoscopic stenting of the stricture. Brown and colleagues reported the use of deconvolutional analysis of Disida time-activity curves to distinguish between primarily hepatocellular and primarily biliary tract disease. The former group had a reduced hepatic extraction fraction, whereas it was preserved in the latter. Both groups had impaired biliary excretion. Further refine­ments in this technique may be of clinical use, but we could not define a useful clinical role.

The performance of a cholangiogram remains the gold standard for stricture diagnosis. This is particularly true for benign strictures because 64% lacked hepatic duct dilation and, therefore, required cholangiographic diagnosis of the stricture that had been suspected on the basis of clinical find­ings and serum biochemistry. These findings are in agree­ment with those of a study reported from Finland. Despite a high sensitivity for the diagnosis of strictures, the cholangiogram was a poor discriminator between malignant and benign strictures. Benign strictures were usually of a smooth character (77%); however, malignant ones were as well (62%), and three strictures in the series could not be characterized due to nonvisualization as a result of their very narrow calibre.

A cholangiogram is an essential component of the inves­tigation of any stricture because it provides anatomic details such as stricture location and calibre. This will be challenged by the advent of MRCP, which promises to provide noninvasively acquired images of the biliary tree. Recent publica­tions suggest that its diagnostic accuracy approaches that of ERCP. ERCP also provides the opportunity for therapeutic intervention for biliary strictures. MRCP was not formally evaluated in this protocol because our institu­tion was not performing them at the time that this study was initiated. Endoscopic ultrasound is another promising tech­nology that can provide information not only about the na­ture and location of the stricture, but also in regard to regional spread. It will be limited by the special exper­tise required for its application and is unlikely to be widely available in the near future.

This prospective study of biliary strictures shows that se­rum bilirubin is an important discriminator between malig­nant and benign strictures and that ultrasound is particularly useful in the diagnosis of malignant strictures, but often misses benign strictures. ERCP enables accurate anatomic diagnosis and provides the opportunity for etiological diag­nosis with cytology brushings and for stenting to relieve ob­struction in selected cases. Disida scanning added little additional information.

MRCP and endoscopic ultrasound will assume an increas­ingly important diagnostic role in the future. It is of critical importance that we continue to evaluate these exciting new technologies prospectively. Only then will they be most effi­ciently applied for patients with biliary obstruction.
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