Multidetector CT is an important tool that offers effective preoperative assessment and early postoperative detection of complications in liver transplant patients. With the increasing number of transplant patients and their improved survival, these patients may be seen in many settings beyond the transplant institution. Radiologists must be familiar with the clinical abnormalities that can occur in posttransplant patients to provide accurate CT interpretation, which can guide appropriate patient management.
are Consultant Radiologists, Department of Radiology, King's
College Hospital, London, England.
Transplantation is an established treatment for end-stage liver
disease, whatever the precipitating cause. Imaging of both the pre-
and posttransplant patient is an important facet of patient
management. Advances in immunosuppressive therapy, surgical
techniques, perioperative care, and imaging have combined to
improve the outcome of liver transplantation; 1-year survival is
now >85%, with a quoted 5-year survival rate of 65% to 78%.
Graft survival relies on prompt diagnosis of complications.
Although there is a reliance on ultrasound (US) for assessing
vascular and nonvascular complications, particularly in Europe,
there is an important role for computed tomography (CT). CT imaging
in the peri- and postoperative phase is used in the evaluation and
diagnosis of vascular and biliary complications, focal collections
(bile or infective), and hematomas, and for the assessment of the
presence of pelvic fluid collections. Postoperative disease
recurrence and posttransplant lymphoproliferative disease (PTLD)
may be readily detected with CT.
Radiological assessment of the liver transplant
Preoperative clinical and radiologic evaluation of the
transplant candidate is essential for appropriate patient
The objectives of preoperative radiologic evaluation in the
recipient include assessment of vessel anatomy and patency as well
as exclusion of intra- and extrahepatic malignancy. Identification
of cirrhosis, sequelae of portal hypertension, and quantification
of the volume of the diseased liver may be performed. Further
information available on CT that is useful to the transplant
surgeon includes the status of the celiac artery, the presence of
splenic artery aneurysms, and the position of any spontaneous
portosystemic venous shunts.
A shortage of cadaver donor livers has led to the institution of
"live-related" donor transplantation. In the preoperative period, a
CT of the donor assesses liver volume and vascular anatomy,
excludes focal liver lesions, and identifies any unsuspected
anomalies that would preclude surgery.
The typical cirrhotic liver morphology shows hypertrophy of the
caudate lobe (segment I according to the Couinaud classification)
and the left lateral liver segments (segments II and III), with
atrophy of the remaining liver (Figure 1). The presence of
congestive splenomegaly, ascites, and portosystemic collaterals
allows for the documentation of portal hypertension.
Most candidates for liver transplant will have cirrhosis and,
with it, a greater risk of an associated hepatocellular carcinoma
(HCC). Screening for HCC should be performed preoperatively.
However, the presence of HCC does not preclude transplantation, and
in some instances, transplantation is curative.
The presence of lesions ≥5 cm in diameter, the presence of ≥3
lesions (the "Milan criteria"), or evidence of extra-hepatic spread
are accepted contraindications to transplantation.
Hepatocellular carcinomas are best visualized on arterial-phase
images, where they appear as avidly enhancing nodules that become
hypodense on the portal-venous phase (Figure 2).
Larger lesions tend to have a typical mosaic enhancement pattern
and may show a peripheral capsule.
Portal vein (PV) and hepatic vein involvement from tumor extension
is also characteristic. The preoperative detection of a
cholangiocarcinoma is an absolute contraindication to liver
transplantation. The rate of recurrence is reported to be as high
Assessment of the liver volume is important in live-related
donors, both to ensure that adequate liver volumes remain in the
donor and that an adequate volume of liver is transplanted into the
recipient; liver graft size is one of the major factors that
determines a successful outcome. A graft that is too large for the
recipient is associated with a risk of graft compression, which
leads to poor vascular perfusion. Conversely, a liver graft that is
too small for the recipient may cause postoperative liver failure
or primary nonfunction.
The volume of a cross-sectional area of liver seen on a given CT
image can be determined simply from a mechanical tracing of the
liver outline, which is then multiplied by the slice thickness to
obtain the volume of liver represented by that image.
CT-determined volumes have been shown to be accurate and
reproducible (Figure 3).
Knowledge of the exact arterial supply to the liver may be
important to the surgeon when planning vascular reconstruction, as
numerous variations in the normal vascular supply exist.
The advent of multislice CT allows rapid evaluation of large
volumes of the liver with excellent spatial resolution. CT
angiography (CTA), with 3-dimensional (3D) or
maximum-intensity-projection (MIP) arterial reconstructions, has
been shown to have a significant impact on surgical planning for
Furthermore, 3D CT arteriography allows for accurate planning of
the transsection plane in live-related donor transplantation.
The arterial anatomy is of particular importance in live-related
transplantation selection, as up to one third of donors are
ineligible for transplant following identification of unsuitable
anatomy of segments II and III.
Portal-vein occlusion occurs in up to 10% of patients with
The presence of PV thrombosis does not preclude surgery, but
preoperative recognition on contrast-enhanced CT facilitates
appropriate surgical strategies, such as a venous "jump-graft" from
the superior mesenteric vein (SMV) to the donor PV.
Size discrepancy between the donor and recipient PV may necessitate
a donor-iliac vein graft to connect the SMV to the PV.
Splenic artery aneurysms occur in patients with cirrhosis and
portal hypertension and are thought to be a consequence of
increased flow in the splenic artery.
Therefore, preoperative identification on CT is important, as there
is increased risk of rupture of splenic artery aneurysms following
liver transplantation (Figure 4). This area is not routinely
visualized at the time of surgery. Preoperative identification of
porto-systemic shunts and varices is also useful, as these may be
ligated at surgery to optimize blood flow toward the liver.
Preoperative identification may also minimize dissection time.
Most deaths occur in the first 6 months following orthotopic
liver transplant, so prompt diagnosis of complications is critical
for graft salvage. Noninvasive imaging-both US and CT-allows for
patient assessment when clinical signs and symptoms advocate,
allowing for early management.
Orthotopic liver transplant using the "piggy-back" technique
requires at least 3 vascular anastomoses: extrahepatic portal vein,
hepatic artery, and suprahepatic vena cava with the adjoining
hepatic veins. The inferior vena cava (IVC) is preserved, and the
caval anastomosis is performed on a common ostium formed from the 3
suprahepatic veins. In this scenario, thrombosis is expected to
occur in the ligated infra-hepatic donor IVC and should not be
misinterpreted as thrombosis on contrast-enhanced CT.
A fourth anastomoses is performed when the liver is placed in the
standard orthotopic position; the infrahepatic donor vena cava is
anastomosed to the recipient infrahepatic vena cava, and the
superhepatic vena cava anastomoses are retained. Modifications to
the standard technique may sometimes be necessary; if the celiac
axis or hepatic artery flow is significantly decreased on
contrast-enhanced CT, the donor iliac artery may be grafted from
the recipient aorta to the donor hepatic artery. This "conduit"
will minimize the possibility of postoperative graft infarction.
CT angiography allows for the detection of hepatic arterial
Often, CTA is used as the second-line investigation in the
diagnostic algorithm for hepatic artery thrombosis after the use of
color Doppler US.
Hepatic artery thrombosis
The hepatic artery is the sole arterial supply to the biliary
system after liver transplantation; all potential collaterals have
been severed, and hepatic artery occlusion "de-arterializes" the
liver and biliary tree (Figure 5).
Hepatic artery thrombosis is the most common vascular complication
of liver transplantation, with a prevalence of 4% to 12% in adult
recipients and up to 40% in children, usually occurring within 2
months of liver transplantation.
Proposed risk factors include the surgical difficulties related to
the anatomic site of the anastomoses, arterial anomalies, the use
of vascular conduits, small arterial size (<3 mm), and the need
to surgically revise the anastomoses.
Clinical presentation varies from mild elevation of liver enzymes
to delayed bile leak, biliary strictures or ischemia leading to
relapsing bacteremia, or fulminate hepatic ne-crosis.
Management is surgical, either with an arterial thrombectomy or
liver retransplantation. With retransplantation, mortality is up to
27%, but without retransplantation, the mortality is approximately
Color Doppler US is the initial imaging technique used for
hepatic artery evaluation in the immediate posttransplant period.
However, it may produce false-negative results because of the
presence of periportal collateral arteries that bypass the occluded
segment of the hepatic artery and reconstitute intrahepatic
Color Doppler US has a quoted sensitivity of 80% to 90% and is
improved with the addition of microbubble US contrast media.
CT angiography with MIP is accurate in imaging the hepatic artery
to confirm or refute ultrasonically suspected hepatic artery
thrombosis or stenosis, with quoted sensitivities of 100%, and
accuracy of 95% in the detection of all vascular complications
The role of CTA is essentially the second-line investigation in the
diagnostic algorithm for hepatic artery thrombosis, following an
equivocal color Doppler US.
Sequela of hepatic artery thrombosis can also be visualized.
Hepatic artery vascular insufficiency from either stenosis or
thrombosis may lead to necrosis of bile duct epithelium, which may
lead to hepatic infarction, bilomas, abscesses, and nonanastomotic
bile leak. In one series, 86% of transplant patients with hepatic
abscesses or infarction were found to have hepatic artery
On CT, 3 general appearances of hepatic infarction may be seen:
peripheral wedge-shaped lesions, rounded lesions that may be
peripheral or central, and irregularly shaped lesions that follow
the course of the bile ducts (Figure 6).
Hepatic artery stenosis
The reported prevalence of hepatic artery stenosis varies from
5% to 11%. It is the second most common vascular complication after
thrombosis, and usually occurs at the anastomotic site within 3
months of transplantation.
Early detection is important, as the stenosis is amenable either to
balloon dilatation or surgical intervention. If untreated, hepatic
artery stenosis may cause hepatic ischemia, hepatic artery
thrombosis, and, ultimately, graft loss.
Revascularization procedures are usually successful, with long-term
graft and patient survival assured. Comparison of 3D CTA, using MIP
and shaded-surface display techniques, with conventional
angiography have shown CTA to be a practical noninvasive method of
diagnosing hepatic artery stenosis (Figure 7).
Hepatic artery pseudoaneurysm
Hepatic artery pseudoaneurysms are uncommon, with a reported
incidence of 1% to 2%, often caused by a combination of infection
and surgical technical malfunction.
Hepatic artery pseudoaneurysms most often occur in the second and
third week after transplantation. Presentation may be nonspecific
with hemobilia, unexplained fever, graft dysfunction, or a falling
hemoglobin level. Hepatic artery thrombosis may occur as a
consequence. The hepatic artery pseudoaneurysm may be intra- or
extrahepatic; when intra-hepatic, it is often related to an
iatrogenic cause (eg, biopsy) and when extrahepatic, it is often
caused by infection. The diagnosis may be difficult. CT may show a
low-attenuation area that enhances with intravenous contrast,
either within the liver or related to the porta hepatis (Figure 8).
However, if partial thrombosis is present within the
pseudoaneurysm, it may be missed. Secondary signs of ischemia on CT
may indicate the need for angiography.
Portal vein thrombosis and stenosis
Portal-vein complications are rare, with an incidence of 1% to
The narrowing of the vessel that is suggestive of stenosis may be
seen on CT, but the functional significance should be confirmed
with pressure-gradient measurement at angiography. Similar features
may be found with a donor-recipient size discrepancy.
In cases of functionally significant stenosis or of PV thrombosis,
secondary features of portal hypertension may be evident on CT,
such as varices, bowel edema, and ascites.
Portal-vein thrombosis is evident on contrast-enhanced CT as a
low-attenuation lesion within the involved portal venous segment
with or without expansion of the vessel, with possible enhancement
at the margin of the thrombus.
Thrombosis of the PV, SMV, or IVC after liver transplantation is
seen almost exclusively in pediatric recipients (Figure 9).
Inferior vena cava stenosis and thrombosis
Complications that involve the hepatic veins and IVC occur in
<1% of patients.
Inferior vena cava stenosis or thrombosis is usually related to the
surgical anastomoses site or to the presence of a hypercoagulable
As with PV stenosis, the functional significance of IVC stenosis
requires confirmation with measurement of the pressure gradient
across the stenosis. The possibility of stenosis is increased with
the "piggy-back" technique, especially when the right hepatic vein
is ligated to match the size between the donor and recipient IVC.
The treatment of choice in IVC stenosis is balloon dilatation.
Despite improvements in surgical technique, biliary tract
complications remain an important cause of morbidity and mortality
in up to 15% to 30% of transplant patients.
Early diagnosis and prompt intervention has decreased mortality.
Most biliary complications occur within 3 months following
transplantation, although some, such as strictures and stone
formation, can develop months to years later.
Although biliary leakage and anastomotic obstruction (partial or
complete) are the most common complications, other potential
problems include dysfunction of the ampulla, mucoceles,
intrahepatic biliary strictures, "bile cast" syndrome, bilomas,
hepatic abscesses, biliary stones, and stent-related complications
Bile leak resulting from bile duct necrosis secondary to hepatic
ischemia or liver biopsy may also occur.
T-tube cholangiography, magnetic resonance cholangiopancreatography
(MRCP), and US are the best noninvasive means for evaluating the
biliary tree. CT is best used to reveal associated biliary
complications (Figure 11).
Bilomas that are adjacent to the site of the bile leak may be
visualized and drained by percutaneous methods using CT guidance.
The coexistence of arterial pathology with biliary complications
must be considered in the case of non-anastomotic bile leaks, as a
biliary reconstruction or revision in the presence of an inadequate
arterial supply will inevitably result in further complications.
Careful assessment of the hepatic artery on CT is essential in
patients with nonanastomotic bile leaks. When arterial problems are
encountered in the context of bilomas, drainage may offer temporary
relief from symptoms, but the definitive solution is usually
Strictures, either anastomotic or non-anastomotic, occur in 4%
to 17% of grafts.
Most biliary strictures occur at the anastomotic site and are
probably caused by scarring and retraction after surgery, although
the anastomoses may be involved by the same processes (such as
ischemia) that lead to nonanastomotic strictures.
Nonanastomotic strictures, often ischemic in origin, are also
caused by infection, chronic rejection, prolonged cold preservation
time, cytomegalovirus (CMV) or
infection, or recurrence of primary sclerosing cholangitis.
If a stricture is suspected and CT does not show any biliary
dilatation, endoscopic retrograde cholangiopancreatography or
percutaneous transhepatic cholangiography should be performed, as
many liver transplants do not develop bile duct dilatation, even
when there is high-grade narrowing.
Fluid collections and hematoma
The majority of patients develop a right-sided pleural effusion
that tends to be a transudate and generally resolves within a few
If the pleural effusion does not resolve and enlarges, then
patients should be evaluated for subdiaphragmatic abnormalities. Up
to 70% of patients with an enlarging pleural effusion 3 days after
liver transplant will exhibit a sub-diaphragmatic abnormality, such
as an abscess or a hematoma (Figure 12).
Small parahepatic hematomas are common after surgery, and these
tend to occur in the gallbladder fossa and the hepatorenal space.
Hematomas may be distinguished on CT imaging from other fluid
collections by their higher attenuation coefficient.
Hematomas usually resolve without complication, and intervention is
not indicated, unless superimposed infection is suspected.
Abscess formation complicates up to 10% of liver
In the presence of symptoms of an infection, CT is the
investigation of choice, particularly if an US examination is
inconclusive. However, no single imaging modality can determine if
a collection is infected or not, and percutaneous aspiration will
be necessary in septic patients.
Extrahepatic abscesses tend to occur in the subphrenic or
subhepatic spaces, and percutaneous drainage is normally feasible.
Intrahepatic abscesses frequently occur as a result of vascular
compromise or arise as an infected biloma secondary to stricture
formation (Figure 13). Percutaneous drainage may be performed, but
correction of the underlying cause must be addressed. Collections
around the porta hepatis may be associated with hepatic artery
pseudoaneurysm formation, so particular attention must be paid to
the vessels in this area on CT imaging, and correlation with color
Doppler US is necessary prior to needle placement for drainage.
Spontaneous hemorrhage in the postoperative period occurs in
<10% of patients and may occur secondary to breakdown of
vascular anastomoses, pseudoaneurysm rupture, or bleeding after
This is usually a clinical diagnosis, although CT has a role in
stable equivocal patients and may reveal the site of bleeding if
there is active extravasation.
Posttransplantation lymphoproliferative disorder
Posttransplantation lymphoproliferative disorder (PTLD) occurs
in 2% to 10% of adults, with a higher incidence in children and may
present as early as 1 month posttransplant.
Recognition of the CT findings of PTLD is important, as early
diagnosis may result in an improved response to therapy. Extranodal
disease is the most common presentation. The liver and
gastrointestinal tract are the most common sites of disease; the
liver is involved in 50% of cases. Within the liver, PTLD can
manifest as multiple discrete nodular low-attenuation lesions on
contrast-enhanced CT (Figure 14), an infiltrative pattern,
consisting of a geographic or an ill-defined region of low
attenuation with or without hepatomegaly, and, lastly, as a
periportal mass that extends into the biliary tree with associated
With PTLD, CT of involved hollow organ viscera shows localized
circumferential wall thickening, dilatation of involved loops,
luminal excavation or ulceration, eccentric polypoid masses,
extramural extension, and intussusception. Lymph node involvement
is seen in 22% of cases, with the lymph nodes at the porta hepatis
and celiac axis most commonly involved. Splenic involvement is
revealed on CT by the presence of splenomegaly and focal
CT-guided biopsy can be performed to confirm the diagnosis.
Liver transplantation for HCC provides excellent outcomes,
applying the Milan criteria, with 5-year survival rates of 70% and
low recurrence rates.
The liver, lung, and bone are the most frequent sites of disease
Most liver diseases for which liver transplantation is performed
recur after liver transplantation. The clinical impact of
recurrence varies. For autoimmune liver diseases (such as primary
biliary cirrhosis, primary sclerosing cholangitis, and autoimmune
hepatitis), clinically significant recurrence appears to be
Cirrhosis secondary to hepatitis C is the leading indication for
liver transplantation in the United States. Hepatitis C viremia
after liver transplantation has been reported in 75% to 95% of
patients, with clinical as well as histologic recurrence in 40% to
60% of patients.
Although CT cannot diagnose disease recurrence, it will show a
cirrhotic configuration to the liver in established cirrhosis.
Other miscellaneous abdominal complications that can occur include
splenic infarction, right adrenal infarction due to ligation of the
right adrenal vein, rupture of a splenic pseudoaneurysm, and bowel
obstruction secondary to adhesions.
Infection affects up to 70% of liver transplant recipients and
is the second most common complication after rejection and graft
dysfunction. The majority of symptomatic infections are bacterial
and relate to surgery, ventilation, and intravenous cannulae.
Cytomegalovirus infection occurs in 45% to 100% of recipients but
is asymptomatic in the majority of patients. Fungal infections are
primarily due to
but infections due to
occur in approximately 6% and carry a high mortality. CT imaging of
the chest, abdomen, and brain may be helpful in establishing the
diagnosis in selected cases.
Rejection occurs in more than one third of transplant
recipients. There are no specific CT imaging features that are
diagnostic of rejection, but CT serves to exclude other causes of
elevated liver enzymes.
Multidetector CT imaging is an invaluable technique for
evaluating the pre- and postoperative liver transplant patient,
allowing for the accurate assessment of the pretransplant candidate
and the early detection of complications. A sound understanding of
the clinical abnormalities that can occur following transplantation
will allow the radiologist to make a sound interpretation of the CT
findings, which then enables rapid implementation of the correct