Diagnostic ultrasound ( PDFDrive )

1766 PART V Pediatric Sonography
in advanced cirrhosis) or if Doppler low studies are equivocal,
MRI or angiography may be performed. Children with biliary
atresia may have an associated polysplenia syndrome (see Fig.
51.8C-G), which includes intestinal malrotation, bilaterally
symmetrical patterns of the major bronchi, abnormal location
of the portal vein anterior to the duodenum, and interruption
of the IVC. 15,90 Liver transplantation may be more diicult in
these children. It is essential that the surgeon be aware of this
anatomic abnormality before transplantation.
In addition, portocaval or mesenteric-caval shunts, whether
created surgically or occurring naturally, change both the low
pattern and the caliber of the main portal vein and may alter
the surgical approach to transplantation. he anatomic variants
of the hepatic artery are not always demonstrated on sonography,
but angiography is rarely performed for the purpose of outlining
the anatomy of the hepatic artery. he examination of the child
before transplantation should also include several organs: the
kidneys, lungs, heart, and intestinal tract. 90,92 During liver
transplantation in the child, the donor hepatic artery is sometimes
removed with a cuf of aorta and anastomosed to the recipient’s
abdominal aorta or iliac artery. An adult liver is usually divided
before being transplanted into a small child. Although the let
lobe (segments 2 and 3) is preferred, an adult liver may be divided
and used for two recipients. A transient luid collection oten
forms around the cut surface of the transplanted lobe or segments,
even though the cut is packed with hemostatic material such as
Gelfoam or ibrin glue. Because the anatomy involved in segmental
or lobar liver transplantation difers considerably from the normal
anatomy and from the anatomy involved in whole-organ transplantation,
a diagram of the procedure is a useful guide for the
sonographer assessing patency of anastomosed vessels.
Posttransplantation Evaluation
he most common complications in the immediate postoperative
period are hepatic artery stenosis, spasm, and thrombosis.
Although collateral vessels may form in the child and shunt
arterial blood into the liver, bile duct injury frequently occurs,
followed by the formation of bile lakes and recurrent infection.
Retransplantation is almost invariably necessary.
Immediate Doppler examination either in the surgical suite
or at the child’s bedside soon ater surgery and then daily for 5
to 7 days is typically performed to conirm patency of the
anastomosed vessels, before clinical or biochemical liver examination
indings become abnormal. 93 he hepatic arterial anastomosis
can be diicult to see adjacent to the Roux loop, so it is important
to examine the intrahepatic arterial branches adjacent to intrahepatic
portal veins, with both gray-scale and Doppler techniques.
Optimal sites for the detection of hepatic arterial Doppler signals
in whole-liver transplants are adjacent to the umbilical branch
of the let portal vein and adjacent to the branch to segments 3
and 4, and alongside the right portal vein and the branches to
segments 6 and 7. he presence of arterial signals at these sites
usually establishes patency of the hepatic artery. In segmental
liver transplants, the “porta hepatis” is located eccentrically along
the right lateral costal margin. 94-96 Given the variability of grat
size and orientation in the right upper quadrant, the sonographer
must ind optimal imaging windows by trial and error. In the
immediate postoperative period, hepatic arterial low (both systolic
and diastolic) is generally brisk. However, in the next 2 to 3 days,
grat edema may result in transiently decreased diastolic low.
As long as systolic upstroke remains sharp and there are other
signs of grat swelling (i.e., periportal edema), patients are watched
expectantly. If the patient’s liver enzyme levels rise, further Doppler
evaluation or surgical reexploration is generally performed.
Tardus-parvus waveforms in the hepatic artery in the immediate
perioperative period are most likely related to arterial spasm
and are treated pharmacologically.
Children with clinically undetected, chronic obstruction of
the main hepatic artery have been reported in whom dampened
intrahepatic arterial low was detected with Doppler
sonography. Angiography in these patients shows obstruction
of the hepatic artery and liver perfusion through extensive
arterial collaterals around the site of a portoenterostomy at the
porta hepatis.
In patients well enough to eat or receive gastric tube feedings,
remember that hepatic arterial Doppler shits are diicult to
detect ater a meal. 70 A repeat examination ater a fast may show
much stronger signals. Failure to detect intrahepatic arterial
Doppler shits indicates thrombosis or a prethrombotic state.
Given the risk of grat injury, arteriography is generally performed
in this situation, with the intent to treat with thrombolytics or
angioplasty.
Although hepatic artery interrogation is the most important
part of the posttransplant examination, the Doppler study is also
helpful in assessing the patency of the venous anastomoses—the
portal and hepatic veins and the IVC. he sites of venous
anastomosis are clearly visible with gray-scale sonography and
should be demonstrated (Fig. 51.36). Portal venous thrombosis
at the anastomosis may occur but is less frequent than arterial
occlusion. Turbulence may be expected at the anastomotic site
of the portal vein, especially when there is discrepancy in the
size of anastomosed vessels. Stenosis or compression of the portal
vein is accompanied by locally increased Doppler shits (Fig.
51.37). Portal hypertension may follow. Poststenotic dilation of
the portal vein may occur without serious sequelae. In some
patients with a small portal vein from a segmental transplant,
prolonged fasting may increase hepatic arterial low and make
visualization of the portal vein diicult. A limited follow-up
scan, ater feeding the patient, can vastly improve visualization
of portal venous low.
Inferior vena cava thrombosis is usually asymptomatic
in the child because collateral low through the paravertebral
venous system is quickly established. he sonographic diagnosis
of an IVC thrombus in a child with liver transplantation can
be diicult. he IVC lumen is obliterated by thrombus, and the
vessel becomes very diicult to visualize (Fig. 51.38). However,
even a patent IVC can be diicult to ind because anatomic
relationships are greatly altered in these children. At Doppler
sonography, low in a hemiazygos vein is easily mistaken for low
in the IVC. he IVC is frequently compressed by a large donor
grat, so careful examination of the draining hepatic veins is
important.
During segmental transplantation, the recipient’s IVC is
let intact and the hepatic vein(s) directly anastomosed to the