|ECR 2018 / C-0650|
|Pre-liver transplantation workup; what should the radiologist look for.|
Findings and procedure details
A- Living donor
Cross sectional liver imaging of the donor is mandatory before liver donation to detect any contraindication or finding that may modify the surgical approach.
Preoperatively, the liver parenchyma should be carefully evaluated for incidental diffuse (mainly steatosis) or focal (benign/malignant) conditions and identification of anatomical variants (4) (5).
A-1-Liver volume calculation Fig. 1 :
Precise estimation of the donor’s liver volume is of paramount importance (4).
A minimal residual volume of 30%-40% is required to prevent small-for-size syndrome on the assumption that the liver parenchyma is disease free (i.e. steatosis) (4) (5) (6).
Ideally, the recipient should receive a graft similar in size to the native organ but a minimum corrected graft-to–recipient body weight (GRBW) ratio of 0.8% is still acceptable (3). On the other hand, larger grafts can compromise abdominal closure and lead to respiratory problems (7).
Workstation software can be used to calculate liver volume based on MRI or CT scan images (8).
A-2-Liver Parenchyma evaluation:
Incidental hepatic focal lesions Fig. 2 may be found in the donor and can, in certain situations, compromise the donation process (4). In addition, any diffuse liver disease, such as fatty infiltration Fig. 3 , should be identified and reported) (1).
Inadvertent reporting of any parenchymal abnormality may result in inaccurate liver volume estimation with tragic consequences for the donor whenever the residual functional liver is insufficient (4).
MRI is the gold standard imaging modality for liver parenchyma evaluation.
Anatomical variants of the hepatic vasculature are relatively frequent (9) (10) and can sometimes preclude the donation process. Any variant should be clearly described and reported for an appropriate pre-procedural planification. Furthermore, some anatomical variants are contraindication to liver donation, and if the surgeon is unaware of their presence, the procedure can result in dramatical outcomes on the donor and/or recipient (1).
Small caliber arteries (2-3mm) – mainly found in the case of multiple accessory arteries – are more prone to thrombosis and require a microsurgical approach to be anastomosed (1). A Special attention should be paid to vascularization of segment IV to avoid its indirect injury during right lobe or lateral segment donation (4).
Also, the number, size, patency and drainage site of the hepatic veins must be reported (4).
Any accessory hepatic vein with its drainage site need to be reported in order to avoid accidental vascular injury and subsequent periprocedural hemorrhage or venous drainage compromise of the concerned segment (donor or recipient) (1).
Usually, downstream the bifurcation of the portal vein, the main right portal vein will divide into anteromedial and posterolateral branches. Trifurcation of the portal system will require double anastomosis if right lobe donation is performed and should be noticed (1). Besides, when the right anteromedial branch arises from the left portal vein, the resection of the latter can have deleterious effects on segments IV, V and VII (11).
Accurate arterial and venous anatomical analysis can be done using multiphasic CT scan or MRI together with volume rendering technique (1) (5).
The common hepatic duct (CHD) emerges from the convergence of right and left bile ducts (4).
Preoperative map of the biliary tree with meticulous description of segmental accessory ducts prevent inadvertent section and subsequent complication (4) (12).
Evaluation of the biliary system can be adequately and non-invasively accomplished by MRCP.
Apart from acute fulminant hepatitis, the recipient has usually undergone plenty of imaging studies during the course of the disease. Nevertheless, radiological evaluation of the recipient should be done as close as possible to the transplantation time with an appropriate cross sectional imaging for global evaluation, anatomical description and lesion characterization of the diseased liver (5). Extended workup should also be performed if extrahepatic malignancy is suspected (5).
B-1-Liver size and dysmorphisme:
On imaging, up to 25% of cirrhotic livers may appear normal, while the remaining majority can show irregular contours, heterogeneous parenchyma, right lobe atrophy and hypertrophy of the caudate and left lobes (13). In some cases, severe caudate lobe hypertrophy Fig. 11 can englobe the inferior vena cava (IVC) making its exposure challenging for the surgeon since the IVC need to be preserved in living donor transplantation (1).
The gallbladder is always removed during the procedure, therefore its abnormalities are generally not taken into consideration (1).
B-2-Portal system patency:
Portal venous thrombosis is a potential complication of chronic liver disease and it can be found in about 15% of patients (14). Unless involving the entire porto-mesenteric system Fig. 12 , bland portal venous thrombosis Fig. 13 is not a contraindication for liver transplantation regardless of its chronicity (1) (14).
On the other hand, tumor vein thrombosis Fig. 14 Fig. 15 is an absolute contraindication for liver transplantation (15) (16). Its characterization rely on visualization of a venous filling defect, expending the vessel lumen and enhancing on arterial phase, after intravenous contrast administration, whether on MRI or CT scan (17). Contrast-enhanced US may also be used to differentiate between malignant and bland thrombus by showing an arterial signal in the former (18).
In both cases (tumor and bland thrombosis), the affected liver parenchyma will show a compensatory increased arterial flow (17).
In chronic portal vein thrombosis, collateral pathways will eventually develop forming a cavernoma (1) Fig. 16.
Enlarged varices are portosystemic pathways that develop as a result of sustained severe portal hypertension. The peri-caval and peri-hepatic varices Fig. 17 should be reported due to their association with increased intraoperative bleeding (7).
B-4-Celiac trunk caliber:
Compromised arterial flow to the transplanted liver is a major cause of early postoperative failure. The transplanted liver lacks collateral arterial vessels and the sole blood supply to the biliary structures comes from the hepatic artery (19). Any arterial flow alteration (i.e. celiac trunk stenosis, anastomotic issues) can lead to arterial thrombosis with subsequent necrosis of the biliary network resulting in graft failure (19). Thus, celiac trunk patency needs to be meticulously evaluated before undergoing the transplantation to rule out any stenosis caused by atherosclerosis or median arcuate ligament compression Fig. 18 Fig. 19 .
B-5-Splenic artery caliber Fig. 20 :
In patients with massive splenomegaly from long standing sustained portal hypertension, increased arterial splenic flow will subsequently develop, leading eventually to dilatation of the splenic artery and increased risk of aneurysmal formation (20). In addition, splenic artery diameter exceeding 4 mm and/or a ratio of splenic to hepatic artery exceeding 1.5 have been associated with splenic steal syndrome (21). Thus, Preoperative evaluation of the splenic artery is mandatory (20) for appropriate management.
B-6-Liver tumors evaluation:
HCC is highly associated with liver cirrhosis (1) and is one of the very few neoplastic conditions that can benefit from organ transplantation as a curative treatment. To be eligible for liver transplantation, a patient with HCC needs to meet certain criteria (5). Milan criteria are the most widely used, stipulating that to be eligible for liver transplantation, patients with HCC should present with either only one lesion not exceeding 5 cm or a maximum of three lesions, with none of them measuring more than 3 cm (5).
In patients at high risk for HCC, a hepatic lesion with typical radiological features of HCC doesn’t need histological confirmation of the diagnosis (22) Fig. 21 . The presence of another type of primary liver tumor (i.e. cholangiocarcinoma or hepatocholangiocarcinoma) is an absolute contraindication for liver transplantation (1). For this reason, radiologists should be very careful and report any atypical feature of the encountered lesion (i.e. early peripheral or late central enhancement) to eventually obtain histological proof in case of suspicion Fig. 22 .
It is also critical to report any vascular (portal or hepatic veins) invasion or extrahepatic malignancy (absolute contraindication for transplantation) and proximity of the tumor to major blood vessels, central bile ducts or gallbladder, since these may affect the outcome of the procedure (1) (5).
B-7-Transjugular portosystemic shunt (TIPS) position Fig. 23 :
Some patients undergoing liver transplantation have already a TIPS placed during the course of their disease, usually between the right portal and right hepatic veins. Regardless of the chosen veins, stent extremities should ideally not reach the IVC or the portal trunk to prevent vessel wall injury that will impose resection of the affected venous segment during liver transplantation (23). Resection of an IVC segment is problematic in case of living donor transplantation where the whole recipient IVC needs to be preserved. In addition, resection of a portal trunk portion will reduce the available length for the anastomosis (14).
For these reasons, precise TIPS location needs to be preoperatively documented, preferably by CT scan with multiplanar reformatting (14).