Synopsis

The objectives of this lecture are:

• 1) To suggest a MR imaging technique for the evaluation of the liver transplant 2) To describe the role of MR imaging in the diagnosis of common complications following liver transplantation, with particular attention to the detection and management of biliary complications. 3) To summarize the recent literature on MR-based imaging biomarkers for the assessment of liver allograft function.

Target audience

Objectives

• To suggest a MR imaging technique for the evaluation of the liver transplant
• To describe the role of MR imaging in the diagnosis of common complications following liver transplantation, with particular attention to the detection and management of biliary complications.
• To summarize the recent literature on MR-based imaging biomarkers for the assessment of liver allograft function.

Content

MR Imaging Technique

Magnetic Resonance Cholangiopancreatography (MRCP) is performed to provide a panoramic visualization of the biliary duct system. The study is based on heavily T2-weighted images obtained as 2D para-coronal thick-slab single shot FSE images and/or as 3D thin-slice FSE images usually obtained with respiration compensation techniques [this approach is also named conventional MRC; C-MRC]. When contrast is indicated, we prefer the injection of a hepatobiliary contrast agent such as Gd-EOB-DTPA or Gd-BOPTA. While the images obtained during the dynamic study (i.e. arterial phase, portal venous phase) are used to evaluate vessel patency and liver lesions, the images obtained during the hepatobiliary phase (approximately 20 minutes after injection of Gd-EOB-DTPA and 90-120 minutes after injection of Gd-BOPTA) permit a contrast-enhanced cholangiography given the delayed contrast excretion into the biliary canaliculi [this approach is also named contrast-enhanced MRC; CE-MRC].

Post liver transplant complications

Post-liver transplant complications can be grouped into vascular (arterial; venous), biliary and other (e.g. rejection, abscess, hematoma and malignancy). The lecture will mainly focus on the biliary complications, given the important role of MR imaging in detection and management.

Biliary complications:

MRI/MRCP is the preferred imaging modality for the assessment of the biliary tree and biliary complications in the liver allograft. Biliary complications occur in 5-32% of patients and are the second most common cause of graft dysfunction and loss after rejection. Biliary complications can be divided in early (occurring within 3 months of surgery) and late (occurring months or years after surgery).

Early (usually from hepatic artery stenosis):

• bile leakage (4-5%) – peri-hepatic fluid collections.
• non-anastomotic, ischemic stricture (5-10%).

Late:

• anastomotic stricture; 13-19%.
• stones/cast (5-7%); usually developing as consequence of biliary strictures.
• sphincter of Oddi dysfunction

MRCP is the preferred imaging modality for the detection and classification of severity of biliary anastomotic stricture and for the detection of biliary casts/stones. CE-MRC may be used to identify the source of active bile leaking.

Evaluation of hepatocellular carcinoma recurrence

Liver transplantation is the preferred treatment option for a cirrhotic patient with early stage hepatocellular carcinoma (HCC), since the surgery removes the tumor and the underlying cirrhosis. In about one third of cases, recurrence occurs in the liver allograft. Regular imaging follow-up is performed to improve the probability of an early detection of HCC recurrence as surgical resection remains the preferred management option. A contrast-enhanced study using Gd-BOPTA or Gd-EOB-DTPA is the preferred option in our institution to improve the sensitivity for the detection of small tumors. Of note, the recurrent HCC in the liver may present with an atypical imaging pattern.

Assessment of liver allograft function

MR-imaging based biomarkers have been investigated for the prediction of graft survival probability including diffusion restriction and signal intensity on hepatobiliary phase after injection of Gd-EOB-DTPA. Decreased hepatic uptake of Gd-EOB-DTPA has been associated with inferior short-term graft survival and scores have been developed, including the functional liver imaging score and the relative liver enhancement. Finally, liver stiffness has been shown to be accurate in the detection of recurrent fibrosis in liver allograft.

Acknowledgements

References

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