Type:
Educational Exhibit
Keywords:
Abdomen, Liver, Vascular, Ultrasound, Ultrasound-Colour Doppler, Ultrasound-Spectral Doppler, Education, Acute, Obstruction / Occlusion, Transplantation
Authors:
D. D. C. Khalil, L. L. D. Faria, S. M. S. D. R. Rocha, L. Suzuki
DOI:
10.26044/ecr2023/C-21078
Findings and procedure details
A. Surgical Techniques
The most common techniques are living donor (segments 2 and 3 and a portion of segment 4) and deceased donor (whole-liver transplant or split organ grafting). In any form of transplant, there are 4 major anastomoses: biliary, portal vein, hepatic vein, and hepatic artery.
B. Normal Postoperative Imaging Features
It is mandatory to evaluate liver parenchyma, biliary tree, perihepatic fluid collections, and patency of the intra and extrahepatic vessels.
- A slightly heterogeneous pattern of the liver parenchyma at gray-scale imaging is expected;
- Hepatic artery: a pulsatile waveform with low resistance and antegrade flow. Expected RI ranging from 0.55 to 0.8.
- Hepatic veins and inferior vena cava: directly related to the cardiac cycle and right atrium pressure changes, with multiphasic flow variations, but the better part of the flow is antegrade.
- Portal vein: always above the baseline and mildly oscillating.
C. Complications
C.1. Vascular complications
The most threatening complications affecting patient and graft survival are vascular, thus radiologists should actively look for them and not just find them by chance.
- Hepatic artery (HA) complications are associated with acute hepatic necrosis and biliary ischemia (vascular supply of the biliary ducts is exclusively from the HA).
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- HA Thrombosis: the most common vascular complication. It is an important cause of graft loss, morbidity, and mortality. Imaging findings of hepatic artery thrombosis are the absence of flow in the hepatic artery and intrahepatic branches with echogenic or hypoechogenic luminal thrombus depending on the date of the thrombus.
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- HA Stenosis occurs in less than 15% of liver transplants. The most frequent site of stenosis is anastomosis. Imaging findings of hepatic artery stenosis are focal elevated peak velocity (>200 cm/sec, or an increase in peak velocity of more than two to three times) with aliasing artifact at color Doppler in the site of obstruction; and intrahepatic tardus parvus waveform.
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- Pseudoaneurysm: HA or portal vein pseudoaneurysm is an uncommon complication that occurs at the site of anastomosis or intrahepatic, typically related to percutaneous biopsy, biliary or vascular procedures, and infection.
- Portal Vein (PV) complications have a prevalence estimated at 1%–2% of transplant recipients.
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- PV thrombosis: is frequently identified in the 1st month after transplant. Imaging findings of portal vein thrombosis are vessel narrowing, absence of flow, and an echogenic or hypoechogenic luminal thrombus depending on the date of the thrombus.
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- PV stenosis: Imaging finding of portal vein stenosis is focal color aliasing, with a more than a three-to-fourfold increase in velocity at the stenotic site relative to the prestenotic segment and/or an anastomosis narrower than 3.0 millimeters.
- Hepatic Veins and Inferior Vena Cava (IVC) complications are less frequent than other vascular complications, occurring in less than 2% of cases.
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- IVC and hepatic vein stenosis: are more common after a living-donor liver transplant;
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- IVC and hepatic vein thrombosis: risk factors include technical problems during the transplant, hypercoagulable state, use of intravascular catheters, and compression of vessels by a fluid collection. Imaging finding of IVC and hepatic vein thrombosis is an echogenic luminal thrombus, while the indirect sign is the inversion of the PV flow. Patients may present with liver congestion, ascites, and/or pleural effusion.
C.2. Biliary
The second most frequent cause of graft dysfunction. According to the literature, up to 40% of liver recipients present at least one of these complications:
- Biliary strictures: anastomotic or nonanastomotic.
- Bile leaks (fistula and/or biloma).
- Bile obstruction.
- Biliary cast syndrome - presence of a hardened dark material within the biliary tract that acquires the same shape as the bile ducts.
C.3. Parenchymal and abdominal findings
- Parenchymal - Infarction or intraparenchymal abscesses, may happen in the postoperative period.
- Ascites and fluid collections (seromas and hematomas).
- Cancer - PTLD is the most frequently associated, and may manifest as nodal enlargement or involve abdominal organs.
D. Pitfalls and Tips
There are a few pitfalls we should be aware of :
- Small reactive lymph nodes and periportal edema correlate with the lymphedema and should not be interpreted as a sign of acute rejection. They are secondary to the interruption of normal lymphatic drainage.
- Small amounts of perihepatic fluid and/or hematoma are related to the surgical procedure.
- Fluid collected adjacent to the falciform ligament of the liver.
- Vascular anastomotic edema - in the first few postoperative days we may find elevations in velocity in the anastomotic site. These elevated velocities will spontaneously solve themselves.
- Talking to the surgeons will help you know beforehand possible anatomic variations that might misguide your exam.