Imaging description

Psuedostenosis of the extrahepatic bile duct is a known diagnostic pitfall in magnetic resonance cholangiopancreatography (MRCP). The extrahepatic component of the biliary tree, which includes the common hepatic duct (CHD), left hepatic duct, and common bile duct (CBD), are crossed by the right hepatic artery (RHA) and the gastroduodenal artery (GDA). The pulsatile nature of the artery may result in non-pathologic obstruction of the extrahepatic bile duct, which appears as a focal signal loss on the multisection MIP reconstructed MRCP images. [1,2] It is most commonly seen where the RHA crosses the CHD just inferior to the confluence of the right and left ductal systems (Figures 73.1 and 73.2). The left hepatic duct compression is usually along the dorsal wall, while GDA may cross the middle segment of the CBD on its ventral wall. An apparent pseudostenosis at these levels can be further evaluated by identifying a normal biliary tree on the MRCP source images and identification of the crossing vessel on the coronal non-fat suppressed T2 or MR angiography images. Additional clues of a pseudostenosis include smooth- and short-segment narrowing (< 1cm) and lack of dilation upstream to the obstruction.

Importance

A false positive diagnosis of a biliary stricture or hilar tumor could expose patients to risks of unnecessary invasive testing such as endoscopic retrograde cholangiopancreatography (ERCP) or biopsy.

Typical clinical scenario

Pathologic pseudostenosis of the extrahepatic biliary duct is a normal finding commonly seen at MRCP and has been reported in as many as 21% of patients.

Differential diagnosis

Differential considerations include all the benign and malignant causes of biliary stricture. Benign conditions include post-surgical strictures, Mirizzi syndrome and those related to inflammation (e.g., chronic pancreatitis and sclerosing cholangitis). Malignant causes include strictures caused by pancreatic head carcinoma, cholangiocarcinoma, duodenal carcinoma, or metastasis. The length of obstruction can be helpful to distinguish these entities.