ORGAN TRANSPLANT IMAGING LIVER

List the 4 limitations of transplant imaging.

• Bowel gas overlying the vessels or transplant

• Limited depth of penetration, especially in obese patients

• Scar tissue

• Shortness of breath or rapid respirations

List the 7 major indications for liver transplantation.

• Cirrhosis with complications, including liver failure

• Hepatocellular carcinoma

• Chronic hepatitis B, hepatitis C, or autoimmune hepatitis

• Acetaminophen overdose

• Primary biliary cirrhosis

• Primary sclerosing cholangitis

• Hemochromatosis or Wilson disease

List the 3 main causes of liver graft failure.

• Primary nonfunction — the main cause

• Vascular and biliary complications

• Perioperative bleeding and infection

Explain an en-bloc transplant.

An en-bloc transplant is a simultaneous kidney and liver transplant that requires a unique surgical connection.

List the 3 key features of a cadaveric deceased-donor allograft.

• It is the most common technique

• The entire donor organ is used

• It has 3 main vascular anastomotic sites

List the 3 vascular anastomotic sites in a cadaveric liver transplant.

• Portal vein

• Hepatic artery

• IVC

Explain living-donor segmental liver transplantation.

A portion of the right or left hepatic lobe is surgically removed from the donor and transplanted into the recipient.

List the 2 features of a reduced-size or split deceased-donor allograft.

• The recipient liver is retained and donor tissue is inserted

• It is commonly used in pediatric recipients

How is the hepatic artery anastomosis performed during liver transplantation?

The deceased donor’s celiac axis is harvested using a Carrel patch. A “fish-mouth” end-to-end anastomosis is created with the recipient hepatic artery at the right-left hepatic artery bifurcation or near the origin of the GDA.

How is the portal vein anastomosis performed?

An end-to-end anastomosis is created between the donor and recipient portal veins.

Compare the traditional IVC transplant technique with the piggyback technique.

• Traditional technique: The donor IVC is placed as an interposition graft and requires both suprahepatic and infrahepatic anastomoses with the recipient IVC.

• Piggyback technique: The donor suprahepatic IVC is connected end-to-side with the recipient hepatic venous confluence, and the donor IVC is tied off distally.

How is biliary drainage restored after liver transplantation?

An end-to-end anastomosis is created between the donor common bile duct and the recipient common hepatic duct

What additional surgery is commonly performed during liver transplantation?

A cholecystectomy.

List the 6 components of the preoperative sonographic evaluation.

• Grayscale examination of the liver

• Documentation of liver size

• Documentation of spleen size

• Doppler evaluation of the portal system, hepatic artery, and IVC

• Measurement of portal vein diameter and identification of anomalous vessels

• Evaluation for ascites, shunts, collaterals, masses, and parenchymal abnormalities

List the 6 components of the postoperative sonographic evaluation.

• Evaluate the liver parenchyma for infarction

• Evaluate the biliary tree for leaks

• Assess fluid collections

• Determine patency of the hepatic artery, portal vein, and IVC

• Evaluate the anastomoses when visible

• Document any additional abnormalities

List the 3 Doppler measurements obtained from the hepatic artery.

• Resistive index

• Peak systolic velocity

• Acceleration time

List the 4 normal hepatic artery waveform findings.

• Sharp systolic upstroke

• Acceleration time less than 0.08 seconds

• RI of 0.5–0.8

• PSV less than 200 cm/s

Describe the normal portal vein waveform after liver transplantation.

The portal vein should have monophasic, continuous flow toward the liver, with possible slight respiratory phasicity.

Describe the normal hepatic vein and IVC waveform.

The normal waveform has a phasic, pulsatile “flying W” pattern reflecting right-heart pressure changes.

What can a monophasic hepatic vein or IVC waveform indicate?

It may indicate:

1. Proximal obstruction

2. Thrombosis

3. Stenosis

List the 4 things evaluated on grayscale imaging of a liver transplant.

• Liver texture

• Intrahepatic biliary dilation

• Focal masses

• Extrahepatic fluid collections

Why might slightly elevated hepatic artery velocity with an RI of 0.80 not automatically mean stenosis?

The transplant may still be adjusting to the recipient’s body. The sonographer should also assess:

1. Portal vein prominence and flow

2. Liver lab values

3. Velocities within the liver

4. Vessel tortuosity and the anastomosis

How should separate hepatic arteries supplying different lobes be labeled?

They should be labeled according to the lobe they supply, such as:

1. Right-lobe hepatic artery

2. Left-lobe hepatic artery

Why can portal venous flow become elevated after liver transplantation?

A small donor liver transplanted into a recipient with a larger body habitus may receive excessive portal venous flow.

What complication can elevated portal venous flow cause?

It can contribute to narrowing or stricture of the hepatic artery.

What treatment may be used temporarily when portal venous flow is too high?

A portocaval shunt may be placed until the transplanted liver adjusts.

List the 4 clinical signs of liver transplant rejection.

• Fever or malaise

• Anorexia

• Hepatomegaly

• Elevated serum bilirubin and alkaline phosphatase

List the 4 sonographic findings of acute liver transplant rejection.

• Heterogeneous echo pattern within the liver

• Decreased liver echogenicity

• Poorly defined liver margins

• Increased periportal echogenicity

List the 3 additional imaging modalities that may be used when ultrasound findings are indeterminate.

• CT angiography

• MR angiography

• Conventional angiography

Why may contrast-enhanced ultrasound be useful in transplant vascular evaluation?

It helps delineate the transplant vasculature and is more sensitive to low-velocity blood flow.

List the 7 main vascular complications after liver transplantation.

• Hepatic artery thrombosis

• Hepatic artery stenosis

• Hepatic artery pseudoaneurysm

• Hepatic artery-to-portal vein fistula

• Portal vein thrombosis

• Portal vein stenosis

• Hepatic vein or IVC thrombosis/stenosis

List the 4 major facts about hepatic artery thrombosis.

• It is the most common vascular complication

• It usually occurs within 6 weeks after transplantation

• It may also develop several years later

• It has a high mortality rate

List the 2 main treatment options for hepatic artery thrombosis.

• Retransplantation

• Thrombectomy or thrombolysis

Why is hepatic artery thrombosis especially dangerous in transplant patients?

The hepatic artery is the only vascular supply to the biliary system in transplant patients.

List the 4 biliary complications caused by hepatic artery thrombosis.

• Biliary necrosis

• Bile leaks or bilomas

• Biliary strictures

• Superinfection with abscess formation

What major clinical finding can result from hepatic artery thrombosis?

Liver failure.

List the 8 risk factors for hepatic artery thrombosis.

• Donor-recipient artery size mismatch

• Small vessels

• Underlying hepatic or celiac artery stenosis

• Prolonged ischemic time of the donor liver

• Acute rejection

• Surgical technique

• Previous liver transplant

• CMV infection

List the 3 sonographic findings of hepatic artery thrombosis.

• Absence of flow in the main and intrahepatic arteries

• Progressive decrease in diastolic flow and dampening of PSV

• Hepatic infarcts, abscesses, biliary necrosis, bile leaks, or biliary ductal dilation

List the 4 major facts about hepatic artery stenosis.

• It is the second most common vascular complication

• It may occur early or late

• The anastomosis is the most common site

• It may cause biliary ischemia and necrosis

List the 3 risk factors for hepatic artery stenosis.

• Injury from surgical clamps

• Poor surgical technique

• Rejection

List the 5 Doppler findings of hepatic artery stenosis.

• Focal arterial narrowing

• Increased PSV at the stenosis

• Post-stenotic turbulence

• PSV greater than 200 cm/s

• Distal tardus-parvus waveform

List the 2 distal tardus-parvus criteria for hepatic artery stenosis.

• Acceleration time greater than 0.08 seconds

• RI less than 0.5

Why can a tardus-parvus waveform be normal during the first 24–48 hours after transplant?

Peripheral hepatic vasodilation may occur in response to reperfusion injury.

What should be done if low-grade hepatic artery stenosis has indeterminate Doppler findings?

The patient may be referred for CT angiography.

List the 4 treatment options for hepatic artery stenosis.

• Stent placement

• Angioplasty

• Surgical revision

• Retransplantation

List the 4 major facts about hepatic artery pseudoaneurysms.

• They are uncommon

• They may be clinically asymptomatic

• They are serious because of the risk of rupture and hemorrhage

• Most are extrahepatic

List the 3 sonographic findings of a hepatic artery pseudoaneurysm.

• Cystic lesion on grayscale

• Yin-yang flow on color Doppler

• To-and-fro spectral Doppler pattern above and below the baseline

List the 3 treatment options for hepatic artery pseudoaneurysm.

• Percutaneous embolization

• Covered stent placement

• Surgical revision

What usually causes a hepatic artery-to-portal vein fistula?

It usually develops after a biopsy.

What happens to most small hepatic artery-to-portal vein fistulas?

They resolve spontaneously.

List the 3 Doppler findings of a hepatic artery-to-portal vein fistula.

• Color aliasing or soft-tissue bruit

• Arterialized flow in the draining portal vein branch

• Low-resistance, high-velocity flow in the feeding hepatic artery

List the 6 risk factors for portal vein thrombosis after transplant.

• Previous portal vein surgery, including TIPS

• Previous portal vein thrombosis in the recipient

• Hypercoagulable conditions

• Vessel redundancy

• Donor-recipient vessel mismatch

• Surgical vessel injury

List the 4 clinical findings of portal vein thrombosis.

• Portal hypertension

• GI bleeding

• Ascites

• Liver dysfunction or failure and peripheral edema

List the 2 main Doppler findings of portal vein thrombosis.

• Lack of blood flow in the extrahepatic portal venous segment

• Development of cavernous transformation

Where does portal vein stenosis most commonly occur?

At the anastomosis.

List the 3 ultrasound criteria for portal vein stenosis.

• Focal narrowing of the main portal vein to less than 2.5 mm

• Peak portal vein velocity greater than 125 cm/s

• Stenotic-to-prestenotic velocity ratio greater than approximately 2.5–3:1

How common are hepatic vein and IVC thrombosis or stenosis after liver transplantation?

They are very rare.

List the 3 risk factors for hepatic vein or IVC thrombosis.

• Hypercoagulable states

• Underlying stenosis

• Injury during surgical manipulation

What waveform change may suggest hepatic vein or IVC obstruction?

Loss of the normal phasic, pulsatile waveform with development of monophasic flow.

When do biliary complications most commonly occur?

During the first month after transplantation.

What is the range of clinical presentation for biliary complications?

Symptoms may range from abdominal pain to sepsis.

Where do bile leaks most commonly occur?

At the biliary anastomosis, although they may also occur intrahepatically.

What may cause intrahepatic biliary leakage?

Scarring or fibrosis.

Where should the sonographer look for a fluid collection related to a bile leak?

Near the porta hepatis.

What are the best tests for detecting bile leakage?

• Cholangiography

• ERCP

What vessel should be carefully evaluated when intrahepatic biliary complications are present?

The hepatic artery should be evaluated for:

1. Hepatic artery thrombosis

2. Hepatic artery stenosis

List the 5 fluid collections that may occur after liver transplantation.

• Hematoma

• Abscess

• Biloma

• Seroma

• Ascites

Where are bilomas commonly found?

Near the biliary anastomotic sites.

Where are seromas commonly seen?

Adjacent to the transplanted liver.

List the 8 major Doppler criteria to memorize for liver transplant imaging.

• Normal hepatic artery acceleration time: <0.08 sec

• Normal hepatic artery RI: 0.5–0.8

• Normal hepatic artery PSV: <200 cm/s

• Hepatic artery stenosis PSV: >200 cm/s

• Distal stenosis acceleration time: >0.08 sec

• Distal stenosis RI: <0.5

• Portal vein stenosis velocity: >125 cm/s

The ratio for portal vein stenosis is 2.5:1 and 3:1.

HA RI's range from?

The ratio for portal vein stenosis is

HA RI's range from 0.5-0.7 just like kidneys! That would be considered normal. 

The ratio for portal vein stenosis is 2.5:1 and 3:1.