MRI of cholangitis: traps and tips

Abstract

There are many limitations to the examination of the bile ducts by magnetic resonance imaging, which may be four orders: (1) technical, requiring analysis of Maximum Intensity Projection (MIP) three-dimensional (3D) volume reconstructions as well as native images, the use of T1-weighted sequences obtained in 3D to avoid entry slice phenomena, and knowledge of the inherent limits of the method, the spatial resolution of which is still less than optimal; (2) anatomical: you need to know the appearance of flow artefacts within the bile ducts and the traps that the presence of air or bleeding into the bile ducts can create; you also need to know the characteristic appearance of the indentation caused by the hepatic artery on the bile ducts and the variants and modifications seen in cases of portal biliopathy; (3) semiological: the terms used to describe bile duct abnormalities seen in MRI are often derived from imprecise descriptions used in retrograde cholangiography: irregularities of the bile ducts, a beaded 'string of pearls' appearance, a 'dead tree' appearance; (4) related to a complex disease, cholangitis which is a complex pathological condition, with possible overlaps between different conditions, such as primary sclerosing cholangitis (PSC), secondary sclerosing cholangitis, autoimmune cholangitis. In any case, the diagnosis of cholangiocarcinoma associated with PSC is always difficult. These limitations can be circumvented by using a precise exploration technique comprised of 3D magnetic resonance cholangiography sequences, which allow volume analysis, examination of native slices and of thick or thin MIP reconstructions, and heavily T2-weighted and T1-weighted 3D sequences with and without gadolinium injection, which is not always essential. The examination must be interpreted according to a stereotyped plan that includes (1) examination of the bile ducts, searching for and describing any stenosis, the presence or absence of dilatation, (2) a systematic search for any intrahepatic calculus, (3) examination of the heterogeneity of the liver parenchyma, investigation to find any liver dysmorphia and signs of portal hypertension, (4) analysis of the enhancement of the liver parenchyma and any enhancement of the wall of the bile ducts.

Keywords: Abdomen; Bile ducts; Cholangitis; MRI; Magnetic resonance cholangiography.