Imaging demonstration of diffuse, multifocal strictures and irregularities involving the medium-sized intrahepatic and/or medium- or large-sized extrahepatic ducts is the gold standard for diagnosing PSC (Fig. 8.1). Cholangiographic abnormalities include multiple strictures, saccular dilatations and irregularity of ductal margins [28]. Randomly distributed, short (1–2 mm), annular intrahepatic strictures alternating with normal or slightly dilated segments produce a beaded appearance. Some authors suggest “beading appearance” (Fig. 8.2) as the presence of more than three strictures with alternating dilatation along a bile duct [29]. Strictures usually occur at the bifurcation of ducts and are out of proportion to upstream ductal dilatation [14]. As the fibrosing process worsens, strictures increase and the ducts become obliterated: at this stage the peripheral ducts cannot be visualized at ERCP (“pruned tree” appearance) but are well detected by MRCP as well as complications such as diverticular like extroflessions, saccular dilatations, webs (focal 1–2 mm thick areas of incomplete circumferential narrowing) and biliary stones (Fig. 8.3) [14, 27]. Both intra- and extra-hepatic ducts are usually involved. Lesions are limited to intrahepatic ducts in less than 20 % of cases, and to extra-hepatic ducts in less than 10 %. Cystic duct, gallbladder and pancreatic duct involvement have been described [2]. MRCP and ERCP show different results depending on the involved biliary tract. ERCP ensures a better detection of choledocic irregularities and diameter alterations. The injection of contrast medium through the catheter placed in prepapillary position causes distension of the choledocic tract, allowing better opacification [30]. However, retrograde opacification shows the proximal end of a stricture but may fail to demonstrate the ductal anatomy distal to the stricture. MRCP shows better in visualizing periferical intra-hepatic ducts distal to severe strictures (Fig. 8.4) [30]. Intra-hepatic ductal dilatation is defined by the presence of intra-hepatic bile ducts with diameter equal or superior to that of central ducts or major than 3 mm. A mild dilatation has a maximum diameter of 4 mm, a moderate dilatation has a diameter between 4 and 6 mm and a severe dilatation is larger than 6 mm. There is evidence that the level of intra-hepatic bile duct visualization with MRCP is different between patients affected or not by PSC. In healthy individuals, central ducts contain enough bile in order to be detected by MRCP, while it is difficult to image minor ducts because they contain a negligible amount of bile. In PSC patients peripheral ducts can be imaged more effectively with MRCP in terms of dilatation, which is secondary to strictures in central ducts. Consequently, a good visualization of peripheral intrahepatic bile ducts with MRCP can alarm the radiologist about the presence of a stricture [27]. It should be noted that areas of minimal narrowing may be missed at MRCP and length of stenosis may be overestimated [30].

Before the diagnosis of PSC is established, processes that mimic PSC at cholangiography must be excluded. Cholangiographic findings are similar in primary and secondary cholangitis [28] and a differential diagnosis on the basis of common imaging is not possible. It is not usually possible to differentiate PSC from chronic bacterial cholangitis, parasitic infection of the bile, cholangitis related to acquired immunodeficiency syndrome (AIDS), IgG4-associated cholangitis, infiltrative diseases (such as sarcoidosis, amyloidosis, histiocytosis X) [14, 15]. The distinction between a benign dominant stricture and cholangiocarcinoma (CCA) in a PSC patient is challenging (Figs. 8.5, 8.6). As the key cholangiographic features of PSC are annular strictures out of proportion to upstream dilatation due to extended fibrosis, when these ducts are overdilated other sclerosing processes such as ascending cholangitis or CCA on PSC should be considered. In a meta-analysis study [31] MRCP appeared as less reliable for differentiating malignant from benign causes of biliary obstruction than it was for detecting the presence of biliary obstruction in general. This lower accuracy in identifying a malignant cause may be due to its lower spatial resolution and inadequate depiction of the contour of strictures as compared with direct cholangiography (ERCP and PTC). As a matter of fact MRCP reveals only abnormalities in the duct lumen and needs to be combined with parenchymal transverse sections after contrast media administration to detect intra-hepatic CCA [32]. Recognition of typical CCA delayed accumulation and washout of contrast material, due to its fibrous centre allows a demonstration of extraductal anomalies suspected for CCA at contrast-enhanced CT or MRI. On MRI, periportal changes, manifesting as low signal intensity on T1w images and high signal intensity on T2w and T1w with late contrast enhancement images, are suggestive of CCA if their extent is greater than 1.5 cm. Cholangiographic features that suggest CCA include irregular high grade ductal narrowing with shouldered margins, rapid progression of the strictures, marked ductal dilatation proximal to strictures and polypoid lesions (Fig. 8.6) [14].