|ECR 2018 / C-0241|
|Vascular complications of liver transplantation: what the radiologist should know|
Findings and procedure details
Imaging techniques used in our center are:
● Postoperative Doppler ultrasound at 24-48 h, day 7, first and third month.
● Trans-Kehr cholangiography on days 7 and 90.
● More ultrasound examinations, CT or angiography are made based on the findings on the first ultrasound examination or in case of impaired liver function.
Vascular complications appear early so the Doppler study in the early days should be thorough. They can affect hepatic artery, portal vein or hepatic veins. In this paper the complications of each of these vessels will be explained separately.
Features orthotopic liver transplantation
The most frequently used surgical techniques should be explained in order to properly understand the complications that hepatic artery can present.
Currently, the most common technique is orthotopic liver transplantation: the graft is placed in the right upper quadrant, in the anatomical location of the liver.
To perform this transplant successfully, 4 anastomosis are needed:
● Portal vein.
● Bile duct.
● Anastomosis of the inferior vena cava to the donor hepatic veins.
● Anastomosis of the hepatic artery. Hepatic artery anastomosis receptor at the fork between right and left hepatic arteries or the output of the gastroduodenal artery.
Complications usually affect anastomosis sites, so it is important to know where they exactly are in our patient.
Moreover, should be aware of anatomic variants, both in the donor and in the recipient (Fig 2).
Hepatic artery complications
Thrombosis (Figs 3, 4, 5, 6, 7, 8 and 9)
It is the most serious complication of orthotopic liver transplantation. Depending on the series it occurs approximately in 5 or 10% of cases. It usually is an early complication, but can occur up to 4 months after transplantation. Because of this complication, a Doppler US is performed in the first 48h after surgery.
Doppler ultrasound has a high sensitivity and specificity. It allows not only to know if thrombus is present or not, but also to quantify the degree of stenosis. If thrombosis is complete, no flow is observed.
However, if Doppler flow is not observed, some possibilities should be evaluated: slow flow secondary to vasospasm or low cardiac output. Therefore, results of the Doppler ultrasound examination must be considered inside the clinical context.
One possibility to improve the diagnostic performance of the technique is to use pulsed Doppler or power Doppler.
Sometimes blood flow is not identified and can not be reliably if it is due to thrombosis or technical impossibility. It should be remembered that many of these patients have poor sonographic window because of poor collaboration and surgical dressing materials.
On these occasions diagnostic performance of ultrasound can be improved using contrast enhanced ultrasound (CEUS). Another option is to complete the study with CT angiography or MRI.
MRI has proven diagnostic accuracy similar to ultrasound, while CT angiography may be even higher.
If thrombosis is detected, the treatment of choice is mechanical thrombectomy. In case of not being able to perform this treatment or having obtained bad results, retransplantation should be considered. Retransplantation should be decided the earliest possible to enable the protocol named “zero code”, which will look for a living donor.
Stenosis (Figs 10, 11, 12, 13, 14, 15 and 16)
The place most frequently affected is the anastomosis. Depending on the number, it affects 5 or 10% of cases.
The time elapsed since the transplantation is performed until this involvement appears varies, but it usually occurs in the first three months. The main risk factor is endothelial injury during surgery.
Stricture shows a characteristic pattern on ultrasound doppler.
● Prestenotic segment elevation of resistance index and low flow.
● The stenotic segment displays a very high flow rate and aliasing artifact, due to the turbulent flow. Blood speed is more than 2 m/s and shows a high systolic peak.
● The poststenotic segment present a low resistance index (less than 0.5) and a parvus et tardus morphology of the spectral curves.
An important consideration. Quantification of the flow velocity in the stenosis using Doppler requires the use of a suitable angle. If the transducer is placed parallel or perpendicular to the artery whose speed is to be measured, quantified speeds would be lower than actual.
In addition to knowing these findings, it is important to remember that in the first 3 days after liver transplantation an increased resistance index of hepatic artery (greater than 0.8) is usually found. In this context, it should be considered normal.
If found, it should be monitored until its normalization, usually in the next few days. Typically the resistance index normalizes three days after the transplant.
However, ultrasound does not allow proper quantification of the degree of stenosis: the technique of choice is CT angiography. Using three dimensional curved reformatting is it possible to study the stenosis.
The hepatic artery stenosis requires treatment. First, it should attempt a percutaneous angioplasty. If the procedure fails, surgery is required.
False aneurysm (Figs 17, 18 and 19)
It is a rare complication. Pseudoaneurysm of hepatic artery presents the same features than in other parts of the body.
In ultrasound, they present as a cystic structure with turbulent blood flow within. Typically, due to swirl formed by the inlet and blood outlet, it is possible to observe the sign of yin and yang.
If CT angiography is performed, it characteristically present an arterial enhancement equal to the other arterial vessels, with an equal wash in the later stages.
They are classified according to their location in extrahepatic and intrahepatic.
1. Extrahepatic pseudoaneurysms. Most common site is the arterial anastomosis. They can occur spontaneously or as a complication of plasty performed for treatment of a preexisting stenosis.
2. Intrahepatic pseudoaneurysms. Characteristically, it is a complication of percutaneous liver biopsy. They may also be secondary to bile duct infections. In case of breakage of such aneurysms a portal or biliary fistula can appear. The pseudoaneurysms and fistulas secondary to percutaneous liver biopsies are much more frequent if the biopsy is done in the first days or weeks after transplantation. In fact, according to some series, the risk of developing an arterioportal fistula is approximately 50% for biopsies performed in the first week, dropping to 10% if performed approximately one month after surgery.
In both cases, the treatment consists of coil embolization and stent placement to prevent inflow to pseudoaneurysm. If results of this treatment are not satisfactory, surgical resection can be performed.
Ischemia / liver infarction
Hepatic infarction is very rare in normal patients, since the liver is a richly vascularized organ with blood from different circuits: hepatic artery and portal vein. Inside the liver there are numerous anastomotic vessels and collateral branches.
However, on liver recipient patients, anastomoses are stopped, so the hepatic infarction is much more common. It is usually associated to arterial occlusion.
Complications of portal vein (Figs 20, 21, 22, 23, 24 and 25)
The most common surgical technique is to directly anastomose the portal vein of the donor with the one of the recipient.
However, there are times when this is not possible, because there is a portal thrombus which prevents direct anastomosis. In such cases, it is necessary to remove segment occupied by the thrombus and use a donor vessel bypass. Typically, the selected vessel is the iliac vein.
Another possible technique, although less used, is to arterialize the portal vein: anastomosing donor porta with hepatic artery of the receptor.
Complications of the portal vein usually affect the anastomosis, so it is important to know its location.
Then the most common complications of the portal vein will be explained.
It is a rare complication. It occurs most often in the extrahepatic portal vein. It can be shown by the absence of flow Doppler on ultrasound examination or a filling defect in the contrast enhanced CT scan or MRI.
The treatment is done with angioplasty, stenting or, if unable to perform the treatment with these less invasive techniques, surgery is performed.
Its most common site is the anastomosis. The characteristic findings in each imaging technique are:
● Doppler ultrasound, there is typically an increase in portal blood flow velocity at the point of the anastomosis. Turbulent flow may also appear and produce aliasing artifact. One way to measure the flow velocity at the location of the stenosis is compared with prestenotic speed, which is typically three times higher in case of stenosis.
● CT or MR angiography can observe and quantify the degree of stenosis.
Treatments are angioplasty, stenting, and in case of failure of the prior techniques, surgical resection.
Ischemia / liver infarction
Although much more common in the case of arterial complications, it may also occur as a result of stenosis or portal vein thrombosis.
Complications of the inferior vena cava (Fig 26)
Although less frequent than before, it can also occur. In this case, the diagnosis is particularly interesting extension of the thrombus. Therefore, if CT venography performed, it is interesting the coronal reconstruction.
Usually they occur as a result of the surgical technique or a hypercoagulable state. Diagnosis and treatment is similar to the one of portal vein thrombosis.
Just as in the rest of vessels, the most common site is the anastomosis. It is also possible that an extrinsic compression stenosis occurs, secondary to edema of the graft or fluid collections, hematomas or abscesses. The diagnostic and therapeutic techniques are similar to those described in the portal vein
Complications of hepatic veins
These are rare complications. As in the rest of the vessels, characteristic complications are thrombosis (Budd-Chiari syndrome) and stenosis. They are more common in living donor transplants.
Thematically related posters
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