Diagnostic ultrasound ( PDFDrive )

CHAPTER 18 Organ Transplantation 625
portion. he donor IVC is then anastomosed with two end-to-end
suprahepatic and infrahepatic anastomoses. In an attempt to
preserve the recipient retrohepatic IVC, some techniques advocate
creation of an anastomosis between the donor and recipient IVC
in an end-to-side or side-to-side coniguration (“piggyback”
anastomosis) or an end-to-end anastomosis between the donor
IVC and a common stump of the three hepatic veins. 7 his
piggyback anastomosis also prevents the need for venovenous
bypass and retrocaval dissection, which are required for interposition
of the donor IVC.
he donor and recipient common bile duct (CBD) are usually
anastomosed end to end, ater cholecystectomy. With this
technique the sphincter of Oddi is preserved and acts as a barrier
to the spread of infection. A T tube is typically let in situ for
about 3 months and permits access for cholangiography or other
biliary procedures. he use of a T tube has, however, decreased
owing to an increased risk of bile leak.
When the recipient common hepatic duct is diseased (e.g.,
sclerosing cholangitis), too short, or too narrow in diameter, a
choledochojejunostomy is performed. 7 his procedure involves
an end-to-side anastomosis between the donor bile duct and a
40-cm recipient jejunal loop. It is associated with a higher risk
of bile leaks, bleeding, enteric relux and recurrent cholangitis
compared with an end-to-end anastomosis.
he growing discrepancy between the number of patients
awaiting transplantation and the number of available cadaveric
donor organs has led to a progressive increase in the number of
living related donor transplantations as well as split liver grats
from deceased donors. he recipient liver is replaced with the
right lobe of a living donor. In the pediatric population, the
lateral segment of the let lobe or the entire let lobe has been
used successfully; the relatively small size of the let lobe is not
suicient, however, to sustain adequate liver function in an adult.
Another advantage of using a right lobe (vs. let lobe) as the
donor portion for transplantation is the relative ease of positioning
the right lobe in the right subphrenic space, allowing a technically
less challenging hepatic venous anastomosis, with a decrease in
the incidence of torsion, compared with let lobe grats. 9
For living related transplants, donor surgery consists of
cholecystectomy followed by right hepatectomy, removing segments
V, VI, VII, and VIII as well as the right hepatic vein.
Occasionally an extended right hepatectomy may be done to
include a portion of segment IV and the middle hepatic vein.
However, most surgeons prefer not to remove the middle hepatic
vein, but to leave it intact in the donor because of the intimate
relationship of the middle and let hepatic veins near their drainage
into the IVC. 9
In a split liver grat from a deceased donor, an adult recipient
typically receives a trisegmental grat including the right lobe
and segment IV and a pediatric recipient receives the let lateral
segments. his technique is useful in increasing the numbers of
transplants available but is more complex than when there is a
single recipient.
Regardless of the type of liver transplantation, routine imaging
evaluation of each anastomosis must be assessed with gray-scale
ultrasound, color Doppler, and spectral Doppler interrogation.
To interpret the gray-scale appearance and Doppler features of
these anastomotic regions, the sonographer should be aware of
the surgical techniques used in liver transplantation.
Normal Liver Transplant Ultrasound
he normal liver transplant has a homogeneous or slightly
heterogeneous echotexture on gray-scale ultrasound, appearing
identical to a normal, nontransplanted liver. In the early postoperative
period, there is usually a small amount of free intraperitoneal
luid or small, perihepatic seromas or hematomas, which tend
to resolve within 7 to 10 days.
he biliary tree should have a normal appearance, with an
anechoic lumen and thin, imperceptible walls. If a T tube is in
situ, the adjacent duct wall may appear mildly prominent secondary
to irritation and edema. Ideally, the biliary anastomosis (end
to end or biliary enteric) should be visualized and inspected for
changes in caliber or wall thickness.
Pneumobilia is oten observed in patients with choledochojejunostomy
and appears as bright, echogenic foci with or without
posterior acoustic shadowing in the bile duct lumen. he disappearance
of previously documented pneumobilia should alert
the sonographer to possible interval development of a biliary
stricture at the biliary-enteric anastomosis. In addition, the
sonographer should be aware that intraductal biliary air may
be confused with tiny biliary stones or adjacent hepatic arterial
calciications because these structures can appear identical on
gray-scale imaging (Fig. 18.2).
Vascular patency of the transplanted vessels (hepatic artery,
portal vein, hepatic veins, IVC) is assessed by (1) direct inspection
for narrowing of the diameter, (2) presence of thrombus within
the vessel lumen, and (3) documentation of normal spectral
waveforms with appropriate directional low. Particular attention
should be paid to the anastomotic regions because these areas
have a higher propensity to develop a hemodynamically signiicant
stenosis compared with the remaining vessel. Because intrahepatic
segmental stenoses or occlusions can develop, the hepatic artery
and main portal vein, as well as their major right and let branches,
should be investigated with color and spectral Doppler
(Fig. 18.3).
he normal hepatic artery shows a rapid systolic upstroke,
with an acceleration time (AT; time from end diastole to irst
systolic peak) of less than 100 cm/sec, and continuous low
throughout diastole, with a resistive index (RI) of 0.5 to 0.7. A
normal portal vein is typically smooth in contour, has an anechoic
lumen, and may show a subtle change in caliber at the surgical
anastomosis. he portal veins show continuous, monophasic,
hepatopetal low with mild velocity variations caused by respiration.
he Doppler appearance of the hepatic veins shows a phasic
waveform, relecting physiologic changes in blood low during
the cardiac cycle.
Biliary Complications
Biliary tract complications are an important cause of morbidity
and mortality in 15% to 30% of patients with liver
transplantation. 10-12 Complications related to biliary-enteric
anastomoses usually manifest within the irst month of surgery
and include anastomotic breakdown, bleeding, and an increased
risk of ascending cholangitis from bacterial overgrowth.