Synopsis

Keywords: Body: Digestive

Biliary diseases can be incidentally discovered in clinically asymptomatic patients or during a diagnostic work-up in cholestatic patients. For most pathological conditions, magnetic resonance (MR) with magnetic resonance cholangiopancreatography (MRCP) is recommended as the second step imaging modality after ultrasound.
MR acquisition protocol includes: conventional T2-weighted (T2W) images on coronal and axial planes; heavily 2D/3D T2-weighted MRCP (T2W MRCP) sequences on the coronal and axial planes, the latter centered on the intra-hépatiques bile ducts; axial diffusion-weighted imaging with high b values (>800 s/mm²); 3D T1-weighted after hepato-specific contrast agents administration will provide cholangiogram, besides the assessment of the liver parenchyma.

Biliary diseases include a large spectrum of benign and malignant disorders, which may affect the intra and/or the extra hepatic ducts with or without liver parenchyma involvement (1). Benign biliary diseases can be incidentally discovered in clinically asymptomatic patients during either routine laboratory tests or work-up for other diseases, or alternatively during the diagnostic work-up in cholestatic patient and may present with acute or chronic clinical course and some may progress toward malignancy (1). Patient past and present history may address the diagnosis. Right upper quadrant pain together with fever is suggestive of cholangitis due to obstructive causes most often represented by cholelithiasis. A history of prior hepato-biliary surgery may suggest biliary obstruction secondary to iatrogenic stricture. Family history of cholestatic liver disease is highly suggestive of hereditary/congenital disorder. Some specific conditions such as infection (HIV or more recently COVID-infection), anti-cancer treatment, (immunotherapy-related cholangitis) or other more rare conditions such as eosinophilic cholangitis, should also be considered as possible cause of benign biliary disease (2). Primary malignant conditions are usually adenocarcinoma that can arise from intra (intra-hepatic or peri-hilar cholangiocarcinoma) and extra-hepatic bile ducts (distal cholangiocarcinoma), from the cystic duct or the gallbladder (3). Metastatic involvement of bile ducts can also occur either by direct involvement or secondary due to infiltration or compression by metastatic disease. For most pathological conditions, magnetic resonance (MR) with magnetic resonance cholangiopancreatography (MRCP) is recommended as the second step imaging modality after ultrasound, and its diagnostic performance is comparable to the more invasive endoscopic retrograde cholangiopancreatography (ERCP), which remains the gold standard diagnostic modality for biliary disease. MR acquisition protocol for biliary assessment includes conventional T2-weighted (T2W) images on coronal and axial planes that can be acquired using breath hold or respiratory-triggering approaches which will differ with a better visualization of the peripheral bile ducts on breath-hold acquired images (ref?). Heavily T2-weighted MRCP (T2W MRCP) sequence enhances the signal intensity from relative static fluid within the biliary tract and suppresses the signal from the background structures to obtain cholangiographic images comparable to ERCP. T2W MRCP images can be obtained with two-dimensional (2D) sequence, a thick-slab single–section of 30 to 60 mm thickness obtained with a single-shot breath-hold (3-5s) RARE (rapid acquisition with relaxation enhancement) technique on the coronal plane to visualize the intra and the extra-hepatic biliary tree (ERCP-like images) and on the axial plane, centered on the hepatic hilum, to visualize the intra-hepatic bile ducts. Additional radial acquisitions, coronal or axial oriented, can be performed when overlapping fluid-content structures obscure part of the biliary anatomy. An alternative approach is the three-dimensional (3D) isotropic fast-recovery RARE sequence acquired with respiratory triggering and thin sections. Maximum intensity projection (MIP), multi-planar reformatted and volume-rendered images are then generated (ref). Several pathologic conditions may impair the visualization of the bile ducts on 2D/3D MRCP images related to the presence of pus, blood, air or solid component when an intraductal solid tumour is present. T1-weighted cholangiogram can be obtained after the administration of an hepato-specific contrast agents, such as gadobenate dimeglumine (Gd-BOPTA) (Multihance, Bracco Diagnostics) or gadoxetic acid disodium (gadoxetate disodium, or Gd-EOB-DTPA) (Eovist or Primovist; Bayer Healthcare, Leverkusen, Germany). These hepato-specific contrast agents are actively taken up by normo-functioning hepatocytes via an ATP-dependent organic anion transporting peptide 1 (OATP1) and then excreted into the biliary tree by a multispecific organic anion transporter (cMOAT). Their effect results into a shortening of the T1 relaxation time of the bile. In patients with normal liver function (normal bilirubin levels), approximately after 15-20 minutes for gadoxetic acid disodium or 60-120 minutes for gadobenate dimeglumine (hepato-biliary phase) the intra and extra-hepatic bile ducts will show high signal intensity (T1W cholangiogram) providing information on the bile ducts anatomy. Moreover, by increasing the flip angle of the 3D GRE T1W sequence from 10° to 35° during the hepato-biliary phase, qualitative and quantitative improvement of the visualization of the biliary ducts is observed when compared with conventional T2W MRCP (6). As a matter of fact, conventional T2W MRCP sequences should be acquired before the excretory phase of the hepato-specific contrast agents, either wise the T2-shortening effect of the contrast agent will result into a signal loss on the T2W MRCP images [7]. Furthermore, standard MR acquisition protocol includes diffusion-weighted imaging with high b values (>800 s/mm²), which show signal abnormality within the bile ducts in presence of cholestasis, infectious conditions or of intra-ductal growing tumours (such as IPMN-B).