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Everything you need to know about Computed Tomography (CT) & CT Scanning


Liver: Liver Transplantation : Preoperative CT Evaluation

Harpreet K. Pannu, M.D.1
Warren R. Maley, M.D.2
Elliot K. Fishman, M.D.1


Introduction

Orthotopic liver transplantation is accepted therapy for multiple irreversible acute and chronic liver diseases. Approximately 4000 transplants are performed each year with the majority of livers coming from cadaveric donors. As the number of transplant candidates is almost three times greater than the availability of cadaveric livers, techniques such as split-liver donation and living-related transplantation have been developed.
Split-liver donation involves dividing the cadaveric liver to transplant the lateral segment of the left lobe into a child and the right lobe into an adult. In living-related transplantation, a living donor undergoes partial hepatectomy for donation to a recipient. The left lateral segment is resected for pediatric recipients and the right lobe is usually resected for adult recipients.


Role of computed tomography

Specific questions that can be answered by CT and their influence on the management of recipients and living-related donors are

Recipients-

1) Patency of the portal vein and superior mesenteric vein.
If there is acute portal vein thrombosis - thrombectomy is performed at surgery.
If there is chronic portal vein thrombosis or portal diameter is < 4 mm - a vein graft is obtained from the donor.
If there is diffuse superior mesenteric venous thrombosis - transplantation cannot be performed.

2) Varices secondary to portal hypertension.
If there are extensive perihepatic and pericaval varices - there is increased bleeding during resection of the native liver.

3) Superior and inferior extent of the transjugular portosystemic (TIPS) shunt.
If the shunt tip is in the inferior vena cava (IVC) - there is scarring of the IVC that may require resection and supradiaphragmatic dissection. This may preclude living-related transplantation.
If the shunt tip is in the extrahepatic portal vein - there are increased complications due to peripancreatic resection, pseudoaneurysm and scarring of the portal vein.

4) Patency of the celiac artery.
If there is celiac stenosis - an interposition conduit is placed between the donor hepatic artery and the recipient infrarenal aorta or right common iliac artery.

5) Presence of hepatic lesions.
If there is hepatocellular carcinoma - one mass < 5 cm or up to three masses, each < 3 cm, without extrahepatic metastases, transplantation is performed. Surgery is contraindicated for larger or more numerous masses, vascular invasion, or extrahepatic metastases. Adenopathy is nonspecific and surgical sampling of nodes is performed prior to transplantation.
If there is known cholangiocarcinoma or extrahepatic malignancy - it is an absolute contraindication to transplantation.

Living-related Donors-

1) Hepatic arterial anatomy to the graft lobe.
If there are accessory arteries - multiple anastomoses are required.
If the artery is < 3 mm in size - microsurgical technique is needed to decrease the risk of thrombosis.
Knowledge of the origin of the artery to segment IV (right vs. left hepatic artery) - aids in surgical dissection.

2) Venous and biliary anatomy to the graft lobe.
If there is an accessory hepatic vein or trifurcation of the portal vein and common duct - additional anastomoses are needed.

3) Liver volumes.
If the volume of the remnant liver in the donor is > 35% - transplantation can be performed.
If the volume of the graft lobe is > 40% of the recipient's required volume - transplantation can be performed.
If the volume of the graft lobe is too large - abdomen closure and respiration is compromised in the recipient.

4) Liver parenchyma.
If there is moderate to severe fatty change - donation cannot be performed due to potential graft dysfunction.


CT protocol

Single detector spiral CT-
- Helical scan through the liver with 750 cc water orally and 150 cc of nonionic contrast IV at 3 cc/second
- Arterial phase delay of 25 seconds and venous phase delay of 50 seconds
- Scan collimation 3 mm and table speed 6 mm/second
- Reconstruction interval 2 mm for arterial phase and 2 mm for the venous phase

Multidetector spiral CT-
- Injection parameters and scan delay as for single detector scanner
- Slice collimation 1.25 mm and table feed 6 mm/rotation
- Reconstructed slice width 1 mm for arterial phase and 1 mm for the venous phase


Brief overview of surgical technique in liver transplantation

Recipient total hepatectomy-
1) The hepatic artery, portal vein and common duct are ligated close to the liver.
2) The intrahepatic inferior vena cava (IVC) is resected or is left intact for cadaveric transplants. The IVC is preserved for living-related transplantation.
3) The diseased liver is removed.

Donor partial hepatectomy-
1) The hepatic artery, portal and hepatic veins and bile duct of the graft lobe are isolated.
2) The hepatic parenchyma is dissected to isolate the graft lobe and it is removed.

Implantation of the graft in the recipient-
1) The donor and recipient IVC and portal vein are anastomosed for cadaveric transplants. The donor hepatic vein is anastomosed to the recipient IVC for living-related transplantation.
2) The donor hepatic artery is anastomosed to the recipient hepatic artery in adults. In children with cadaveric transplants, the donor aorta is anastomosed to the distal host aorta.
3) The donor and recipient bile ducts are anastomosed or a choledochojejunostomy is performed.


Variations in liver anatomy

Hepatic arterial-
1) Classic anatomy with the right and left hepatic arteries arising from the proper hepatic artery in 55% of subjects.
2) The right hepatic artery is replaced and arises from the superior mesenteric artery in 11%.
3) The left hepatic artery is replaced and arises from the left gastric artery in 10%.
4) Accessory right or left hepatic arteries are each present in approximately 8% of subjects.

Portal venous-
1) Bifurcation into right and left portal veins.
2) Trifurcation into a left portal vein and two branches to the right lobe -one to segments 6 and 7 and the second branch to segments 5 and 8.

Hepatic venous-
1) The right, left and middle veins drain into the inferior vena cava.
2) Inconstant branches drain from the posterior right lobe directly into the IVC.

Biliary-
1) Single right and left hepatic ducts join to form the common hepatic duct.
2) One or more segmental ducts can join the hepatic duct separately.


Summary

Recipients-
1) Extensive portal vein thrombosis and inappropriate location of TIPS shunt are important to determine because they may preclude living-related transplantation.
2) Diffuse mesenteric thrombosis, advanced hepatocellular cancer and extrahepatic malignancies are contraindications to transplantation.
3) Surgery can be complicated in the presence of perihepatic collateral veins and is modified if there is celiac stenosis.

Living-related donors-
1) The lateral segment of the left lobe is donated to a child and the right lobe is donated to an adult. Evaluation of the vascular anatomy to the graft lobe is important.
2) The volume of the entire liver and graft lobe is assessed. Fatty change usually precludes donation.

© 1999-2019 Elliot K. Fishman, MD, FACR. All rights reserved.