Evolving role of magnetic resonance techniques in primary sclerosing cholangitis

Table 1 Summary of magnetic resonance techniques used in primary sclerosing cholangitis

MR technique	Description of technique	Role in PSC
T2-weighted MRCP	Non-contrast sequences that depict fluid-filled structures such as bile ducts as high-intensity (white) compared to low-intensity (grey/black) of adjacent structures.	Visualisation of biliary anatomy.
Three-dimensional MRCP	Respiratory-triggered, single volume thin slab acquisitions producing isotropic images.	Preferred sequences for optimal multi angle visualisation of the biliary anatomy.
Two-dimensional MRCP	Specific sequences combining coronal thin-slab and rotating oblique-coronal thick-slab image acquisition.	Single shot T2w MRCP sequences are used when three-dimensional MRCP has artefacts or not feasible.
T2-weighted liver axial	Measure of T2 relaxation time in liver parenchyma. Both fat and water appear bright.	Sequence for optimal visualisation of the liver parenchyma.
T1-weighted liver axial	Measure of T1 relaxation time in liver parenchyma. Fat appears bright, water appears dark.	Sequence for optimal visualisation of the liver parenchyma.
MR elastrography	Generates an elastogram map. Specific regions can be selected to obtain mean liver stiffness (kilopascals; kPa).	Quantification and distribution of liver fibrosis.
Diffusion-weighted MRI	Captures changes in the diffusion properties of water protons in tissue represented as the apparent diffusion coefficient.	Can be used to assess liver parenchymal morphological changes (e.g., tumours) and as surrogate for liver fibrosis.
Dynamic contrast-enhanced MRI	Measures T1 changes in liver parenchyma following bolus administration of gadolinium in different phases of uptake and elimination.	Delineates flow in vessels, permeability and enhancement of parenchyma. Can be used to quantify liver function using flow and permeability parameters as surrogate for liver fibrosis.

MR: Magnetic resonance; PSC: Primary sclerosing cholangitis; MRI: Magnetic resonance imaging; MRCP: Magnetic resonance cholangiopancreatography.

Table 2 Descriptive features of primary sclerosing cholangitis on magnetic resonance imaging/ magnetic resonance cholangiopancreatography[22,30-32]

Bile duct changes

Multiple annular or short segmental strictures (1-2 mm) with slightly dilated ducts among them: “beaded” appearance

Obliteration of small peripheral ducts “pruned tree”

Periductal inflammation

Thickening of walls of large ducts

Strictures seen at bile duct bifurcation

Angles between peripheral and central bile ducts become obtuse

Exclusive involvement of extrahepatic bile duct is infrequent

Bile duct dilatations are usually subtle

Retraction of papilla

Webs, diverticula and pigmented stones

Liver parenchymal changes

Segmental or lobular atrophy with compensatory hypertrophy attributed to chronic biliary obstruction

Patchy areas of peripheral parenchymal enhancement

Caudate lobe hypertrophy1

Spherical liver shape2

Peripheral wedge-shaped areas with focal increased signal intensity on T2-weighted images3

T2-weighted hyperintensity around portal vein branches

Regional changes

Gallbladder enlargement

Enlarged regional lymph nodes

Signs of portal hypertension including splenomegaly and collateral vessels

¹Autoimmune process spares bile ducts in caudate lobe that results in compensatory hypertrophy. This feature is also seen in other cirrhotic livers because the caudate lobe has its own venous, lymphatic and biliary drainage.

²This is due to atrophy of left lateral segments and posterior segments of the right lobe.

³It remains unclear if this is caused by inflammatory or fibrotic conditions.

Table 3 The Amsterdam classification of endoscopic retrograde cholangiopancreatography cholangiographic changes in primary sclerosing cholangitis[65]

Type	Intrahepatic	Extrahepatic
0	No visible abnormalities	No visible abnormalities
I	Multiple calibre changes; minimal dilatation	Slight irregularities of duct contour; no stricture
II	Multiple strictures; saccular dilatations, decreased arborisation	Segmental strictures
III	Only central branches filled despite adequate filling pressure; severe pruning	Strictures of almost entire length of duct
IV	-	Extremely irregular margins; diverticulum-like outpouchings