AJR 2001; 177:645-651
© American Roentgen Ray Society
Multidetector CT of Potential Right-Lobe Liver Donors
Ihab R. Kamel1,2,
Jonathan B. Kruskal1,
Mary T. Keogan1,
S. Nahum Goldberg1,
Gisele Warmbrand1 and
Vassilios Raptopoulos1
1
Department of Radiology, Beth Israel Deaconess Medical Center, Harvard Medical
School, 330 Brookline Ave., Boston, MA 02115.
2
Present address: Russell H. Morgan Department of Radiology and Radiological
Sciences, Johns Hopkins University, 600 N. Wolfe St., Baltimore, MD
21287.
Received January 18, 2001;
accepted after revision February 20, 2001.
Address correspondence to I. R. Kamel.
Introduction
One of the most challenging problems in liver transplantation is the
rapidly growing discrepancy between the number of patients on the liver
transplant list and the available cadaveric donors
[1]. Living donor liver
transplantation is an innovative procedure in which the recipient's liver is
explanted and replaced with a portion of the liver from a living donor. The
procedure has been used safely in the pediatric population using the left
lateral segment or the left lobe of the liver
[2]. This success has sparked
an interest in applying the same procedure to adults
[3,
4]. However, grafts obtained
from the left lobe are insufficient to sustain adequate liver function in an
adult. Right-lobe grafts are usually larger than left-lobe grafts, providing
adequate liver mass in an adult recipient
[5]. In previous work, we have
shown the impact of multidetector CT on patient selection and surgical
planning [6]. In this pictorial
essay, we provide details of the various stages of image processing and
emphasize the surgical importance of the relevant anatomic and vascular
variants.
Donor Selection
Donors undergo extensive preoperative physical, laboratory, and
psychological evaluations. Given the complexity of the hepatic resection,
preoperative imaging plays an important role in patient selection and surgical
planning. Multidetector CT has an emerging role in comprehensive preoperative
evaluation of potential donors. It provides a vascular "road map"
critical for surgical guidance. It also provides total liver volume and lobar
volume after virtual right hepatectomy. These volumes are important if one is
to avoid donor—recipient volume mismatch, a common cause of graft
malfunction [5].
Imaging Protocol
Imaging was performed using a multidetector CT scanner (LightSpeed; General
Electric Medical Systems, Milwaukee, WI), as described in our prior study
[6]. Multiphase scanning was
performed after IV injection of 180 mL of ioversol (Optiray; Mallinckrodt, St.
Louis, MO) at a rate of 5 mL/sec. Arterial-dominant-phase images were acquired
at 18 sec (1.25-mm collimation; table speed, 7.5). Portal-dominant-phase
images were acquired at 60 sec (2.5-mm collimation; table speed, 15).
Postprocessing was performed on a commercially available workstation
(Advantage Windows 3.1; General Electric Medical Systems).
Hepatic Arterial Anatomy
The complex vascular anatomy of the liver and the high incidence of
vascular variants reinforce the need for accurate preoperative vascular
imaging. Although none of the arterial variants is considered a
contraindication to donor hepatectomy, the surgeon must have a preoperative
vascular roadmap if the procedure is to be a technical success
[6]. Multidetector CT allows
excellent delineation of the small intrahepatic tertiary branches (Figs.
1A,1B,1C
and 2). In the preoperative
imaging for the donor right lobectomy, the most important artery to delineate
is the artery to segment IV, which could arise from the right or the left
hepatic artery (Figs.
3A,3B
and 4). Its origin may not be
appreciated intraoperatively without significant dissection at the porta
hepatis. When performing a right lobectomy, the surgeon divides the right
hepatic artery distal to the branches to segment IV to ensure adequate blood
supply during the regeneration of the remaining left lobe.
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Fig. 1A. —Hepatic arterial anatomy in potential liver donor,
51-year-old man. Axial images in arterial phase were acquired at 18 sec with
1.25-mm collimation and table speed of 7.5. Reference axial CT image shows
areas selected to be used to generate reconstructed thick slabs along coronal
oblique plane, which is optimum plane to depict hepatic arterial anatomy.
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Fig. 1B. —Hepatic arterial anatomy in potential liver donor,
51-year-old man. Axial images in arterial phase were acquired at 18 sec with
1.25-mm collimation and table speed of 7.5. Maximum-intensity-projection CT
scan in thick slab (2.5 cm) reveals contrast opacification of hepatic arteries
up to tertiary branches. Right (R) and left (L) hepatic arteries are well
visualized. Artery (arrow) to segment IV arises from right hepatic
artery. This vessel should be spared in right hepatectomy.
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Fig. 1C. —Hepatic arterial anatomy in potential liver donor,
51-year-old man. Axial images in arterial phase were acquired at 18 sec with
1.25-mm collimation and table speed of 7.5. Three-dimensional volume-rendered
image with shaded-surface display and posterior cut confirms origin of artery
(arrow) to segment IV from right hepatic artery (R). L = left hepatic
artery.
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Fig. 2. —Hepatic arterial anatomy in potential liver donor,
36-year-old man. Three-dimensional volume-rendered CT image with
shaded-surface display and posterior cut reveals replaced right hepatic artery
(arrow) arising from superior mesenteric artery. This information is
important in preoperative planning.
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Fig. 3A. —Hepatic arterial anatomy in potential liver donor,
37-year-old man. Thick-slab (2.5-cm) maximum-intensity-projection CT scan in
coronal oblique plane centered over porta hepatis reveals artery
(arrow) to segment IV arising from left hepatic artery (L).
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Fig. 3B. —Hepatic arterial anatomy in potential liver donor,
37-year-old man. Thick-slab (2.5-cm) maximum-intensity-projection CT scan in
axial plane reveals artery (arrow) to segment IV and confirms its
origin from left hepatic artery.
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Fig. 4. —Hepatic arterial anatomy in potential liver donor,
50-year-old woman. Thick-slab (2-cm) maximum-intensity-projection CT scan of
hepatic arteries in coronal oblique view. Segment IV arteries
(arrows) arise from right (R) and left (L) hepatic arteries.
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Hepatic Venous Anatomy
The radiologic requirements for hepatic vein delineation depend largely on
the experience and preference of the local surgeons. The axial images obtained
during the portal venous phase best reveal early branching and early
bifurcation of the middle hepatic vein that may alter the right hepatectomy
plane (Fig.
5A,5B,5C).
The site of the confluence of the middle hepatic vein should be identified to
allow the surgeon to anticipate where larger venous structures will need to be
transected. Special attention should be paid to the presence of an accessory
inferior right hepatic vein because it should be preserved during surgery to
reduce the risk of graft malfunction. An accessory inferior right hepatic vein
was identified in 68% of donors
[6]. If this structure is
visualized, its distance from the right hepatic vein should be measured in the
coronal plane (Fig. 6). If the
distance is more than 4 cm, it may be difficult to surgically implant both
veins using a single partially occluding clamp on the recipient's inferior
vena cava. Three-dimensional models can also be obtained and rotated in
multiple planes to assist in preoperative planning
(Fig. 7).
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Fig. 5A. —Hepatic venous anatomy in potential liver donor, 24-year-old
man. Axial portal-venous-phase CT images were acquired at 60 sec with 2.5-mm
collimation and table speed of 15. Reference coronal image used to generate
thick-slab (2.5-cm) maximum-intensity-projection images along axial plane.
Plane shown is optimum for revealing hepatic venous anatomy.
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Fig. 5B. —Hepatic venous anatomy in potential liver donor, 24-year-old
man. Axial portal-venous-phase CT images were acquired at 60 sec with 2.5-mm
collimation and table speed of 15. Volume-rendered axial image obtained
through upper liver reveals adequate contrast opacification of right (R),
middle (M), and left (L) hepatic veins. Note intimate relationship between
middle and left hepatic veins. Because of this intimate relationship, surgeons
prefer not to include middle hepatic vein in right hepatectomy.
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Fig. 5C. —Hepatic venous anatomy in potential liver donor, 24-year-old
man. Axial portal-venous-phase CT images were acquired at 60 sec with 2.5-mm
collimation and table speed of 15. At more inferior position, note two
accessory inferior right hepatic veins (arrows) draining into
inferior vena cava. These vessels should be spared to avoid graft
malfunction.
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Fig. 6. —Hepatic venous anatomy in potential liver donor, 40-year-old
woman. Thick-slab (2-cm) maximum-intensity-projection CT scan of hepatic veins
in coronal plane shows large accessory inferior right hepatic vein
(straight arrow) draining into inferior vena cava. Measuring distance
between this vessel and right hepatic vein (curved arrow) is
important for surgical planning.
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Fig. 7. —Three-dimensional computer model of hepatic veins in
potential liver donor, 42-year-old man. Model is viewed from right superior
oblique position. Right (R), middle (M), and left (L) hepatic veins are well
visualized. This image is essential to identify major branching points to
right of middle hepatic vein, where parenchymal dissection will be undertaken.
Note large branch (arrow) from middle hepatic vein toward right.
Surgeons need to be aware of this finding before surgery because it may
determine site of parenchymal dissection.
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Portal Venous Anatomy
Depending on their experience, surgeons may deem several anatomic portal
vein variants to be relative or absolute contra-indications to donor
hepatectomy (Fig.
8A,8B).
An absence of the right portal vein trunk was reported in 20% of donors
[6] (Figs.
9,10,11).
A right hepatectomy performed in a donor with such anatomic structure may
result in more than one portal vein anastomosis, increasing the risk of
postoperative portal vein thrombosis. The surgeons should be fully aware of
this anatomy because such surgery may be technically challenging.
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Fig. 8A. —Portal venous anatomy in potential liver donor, 31-year-old
man. Axial images were obtained during portal venous phase. Reference axial CT
image is used to generate thick-slab (2.5-cm) maximum intensity projections
along coronal plane centered over portal vein, which is optimum plane to
depict portal venous anatomy.
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Fig. 8B. —Portal venous anatomy in potential liver donor, 31-year-old
man. Axial images were obtained during portal venous phase. Coronal
maximum-intensity-projection CT image reveals contrast medium opacification of
main portal vein (M) and its branches. Note posterior right portal vein
(arrow) arising directly from main portal vein, an anatomic portal
vein variant that some surgeons may deem a contraindication to performing
donor right hepatectomy because of increased risk of postoperative portal vein
thrombosis.
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Fig. 9. —Portal venous anatomy in potential liver donor, 28-year-old
woman. Three-dimensional computer model of portal veins as seen anteriorly
reveals normal portal venous anatomy. Main (M), right (R), and left (L) portal
veins are well visualized. Note vein (arrow) supplying segment IV
arising from right portal vein.
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Fig. 10. —Portal venous anatomy in potential liver donor, 37-year-old
man. Three-dimensional computer model of portal veins as seen anteriorly
reveals trifurcation of main (M) portal vein into anterior right (A),
posterior right (P), and left (L) portal veins. This information is important
for surgical planning.
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Fig. 11. —Portal venous anatomy in potential liver donor, 52-year-old
man. Three-dimensional computer model of portal veins as seen anteriorly
reveals quadrifurcation of main (M) portal vein into anterior right (A),
posterior right (P), vein (arrow) to segment IV, and left (L) portal
veins.
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Total Liver Volume
To sustain metabolic function, accurate volumetric measurements must be
made to provide sufficient liver volume during regeneration. Insufficient
volume will not only result in failed function in a healthy donor, but normal
portal perfusion through a small implanted graft may result in immediate graft
malfunction as sinusoids shut down and blood is shunted away from the liver.
Hand tracing the liver outline on the axial images of the portal venous phase
is an accurate and reproducible method of measuring liver volume
[7]. With hand tracing, one can
carefully isolate the liver from surrounding structures with similar
attenuation. One can also exclude large vessels and major fissures to enhance
measurement accuracy (Figs.
12A,12B,13A,13B,14).
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Fig. 12A. —Hepatic volume determination in potential liver donor,
42-year-old man. Hand tracing is used to visually isolate liver from
surrounding tissues with similar attenuation, using selected axial images
obtained during portal venous phase. Care is exercised to avoid major vessels,
including inferior vena cava (straight arrow), portal vein
(arrowhead), and fissures, including fissure for ligamentum teres
(curved arrow).
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Fig. 13A. —Hepatic volume determination in potential liver donor,
36-year-old woman. Three-dimensional computer model depicting volume of liver
is seen anteriorly. Shape of liver is important because it determines whether
graft can be accommodated in recipient's right upper quadrant.
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Fig. 13B. —Hepatic volume determination in potential liver donor,
36-year-old woman. Three-dimensional computer model of hepatic veins
superimposed on liver model enhances relationship between liver parenchyma and
vascular anatomy. Notice presence of an accessory inferior right hepatic vein
(arrow).
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Fig. 14. —Hepatic volume determination in potential liver donor,
27-year-old man. Three-dimensional computer model depicting volume of liver
with superior cut is seen from anterior oblique view. Three-dimensional models
of hepatic veins (blue) and portal veins (red) are also superimposed. This
view emphasizes relationship between liver parenchyma and vascular
anatomy.
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Virtual Hepatectomy and Lobar Liver Volume
Knowledge of lobar liver volume is important to avoid a donor-recipient
volume mismatch. In general, the minimum graft volume required to provide
sufficient functional hepatocytes is approximately 1% of the recipient's body
weight [5]. Although total
liver volume is reported to have a relatively constant relation to body
weight, right- and left-lobe volumes are widely variable
[8]. Therefore, graft size
cannot be predicted preoperatively by body weight. Using hand tracing permits
one to perform a virtual hepatectomy in a curved plane immediately to the
right of the middle hepatic vein, simulating the anticipated surgical incision
(Fig.
15A,15B).
Subsequently, the right- and left-lobe volumes can be calculated. If
indicated, this plane can be modified depending the vascular variants present
and resultant volumetric measurements.
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Fig. 15A. —Right-lobe volume determination in potential liver donor,
38-year-old man. Three-dimensional computer model of hepatic veins (blue) and
portal vein (red) volume is seen from anterior superior oblique view.
Obtaining such image allows surgeons to predict site of parenchymal dissection
at donor hepatectomy.
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Fig. 15B. —Right-lobe volume determination in potential liver donor,
38-year-old man. Three-dimensional computer model of hepatic veins and portal
vein is superimposed on right lobe of liver after virtual donor hepatectomy.
This model is used to calculate graft volume and to depict major vascular
branches traversing hepatectomy plane. This plane can be interactively
adjusted to satisfy volumetric requirements for donor and matching
recipient.
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Multidetector CT has an emerging role in preoperative evaluation of
potential living donors. The information provided allows better planning for a
safer surgical approach.
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Top
Introduction
Donor Selection
