6i 7
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Diagnosis Children:
Anne M. Hubbard1 James S. Meyer Soroosh Mahboubi
of Liver
Disease
in
Value of MR Angiography
We retrospectively studied the clinical use of MR angiography, a gradient-echo technique susceptible to motion, in the preoperative evaluation of the hepatic vasculature in children with liver disease. Twenty imaging examinations were performed in 18 patients 3 months to 10 years old (mean, 2.3 years). Eleven patients had liver tumors and seven had cirrhosis associated with biliary atresia, cystic fibrosis, and short-bowel syndrome. Respiratory motion artifacts were present in most patients, but all MR angiographic
studies
were
technically
adequate.
Comparing
MR
angiograms
with
spin-
images, we found that vascular visualization was better with MR angiography in 12 cases (60%), equal in five (25%), and worse in three (15%). In 10 of 20 cases, MR angiography provided additional vascular information not present on spin-echo images. MR angiography is a useful adjunct to spin-echo imaging for assessing hepatic vascular anatomy in children with liver disease. echo
AJR
[i
159:617-621,
1992
September
MR imaging is being used increasingly in the evaluation of liven disease in adults It has also been found useful in the evaluation of childhood liver diseases,
].
especially
tumors
[2, 3]. Gradient-echo
flowing angiography is potentially useful in the evaluation of hepatic vessels in liver tumors and in diffuse liven disease in children. In adults, good vascular definition has been obtained by using gradient-echo pulse sequences acquired in a single breath-hold [8]. Inasmuch as breath-holding by children is unreliable or impossible, this technique
blood (MR angiognaphy)
is
usually
not
angiognams this
technique
ventional
Materials
feasible.
obtained
This
study
in children
provides
spin-echo
pulse
are being applied
was
without
additional
done
to
used
the body
evaluate
breath-holding
vascular
(SE) sequences
sequences
throughout
information
to study
[4-7].
the
MR
quality
and to determine when
compared
of
MR
whether with
con-
of the liven.
and Methods
MR angiography was performed in 18 consecutive patients scheduled for MR imaging of liver disease. The patients ranged in age from 3 months to 10 years old (mean, 2.3 years). Eleven patients had liver tumors (three hemangioendotheliomas, five hepatoblastomas, one hepatocellular
carcinoma,
one
embryonal
Two patients with hepatoblastoma Received December 26, 1991 ; accepted after revision February 19, 1992. 1 All authors: Department of Radiology, The Chil-
dren’s
Hospital
Center Blvd., print requests
of Philadelphia, 34th Philadelphia, PA 19104. to A. M. Hubbard.
0361-803X/92/1593-0617 0 American Roentgen Ray Society
St. & Civic Address re-
cell
sarcoma,
were imaged
and
one
metastatic
neuroblastoma).
MR images were obtained before liver liver disease caused by extrahepatic biliary twice.
transplantation in seven patients with diffuse atresia(five), cystic fibrosis (one), and short-bowel syndrome (one). All imaging was performed on a Siemens 1 .5-T Magnetom unit. A knee coil was used for infants (two cases), a head coil for children weighing less than 20 kg (1 7), and a body coil for larger children (one). The
smallest coil into which the child would fit was always chosen, because our experience indicated that this produced the best image quality on SE studies of the chest, abdomen, and pelvis. All patients less than 6 years old were sedated; those less than i 8 months old received chloral hydrate (60-1 20 mg/kg) orally, and those between 18 months and 6 years received
Nembutal
(pentobarbital,
3-6
mg/kg)
IV. Patients
were
monitored
continuously
in
6i 8
HUBBARD
the imager via a digital pulse recorder and pulse oximeter. Coil size and sedation were the only variables in the performance of the
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examinations.
Ti -weighted SE sequences (500/1 5 [TA/TEl, four acquisitions, and 1 92 phase encodings) were obtained in the axial and coronal planes, and T2-weighted sequences (2000/90-120, two acquisitions, and 192 phase encodings) were obtained in the axial plane. Thereafter, two-dimensional sequential fast low-angle shot (FLASH) MR angiograms (25-50/10, 45#{176} flip angle, one acquisition, and 256 phase encodings)
were
obtained
in the axial
5 mm thick with a 20% overlap. was
frequently
flow
to evaluate
used
with
coronal
planes.
Slices
A third MR angiographic
presaturation
specific
and
vessels
were
sequence
of either the arterial or venous on the previous sequences. took 4 mm to perform, adding a
seen
Each MR angiographic sequence maximum of 12 mm to the examination time was 45-60 mm.
time. The total examination
The MR angiographic sequences were reviewed as raw data sets and processed after acquisition by using a maximum-intensity-projection algorithm. The SE images were reviewed first by the radiologists as a group and then used as a guide to evaluate the MR angiographic sequences. On Ti -weighted images, areas of tubular flow void that connected to definitive vascular structures were identified. The major vessels supplying or draining the liver (aorta, hepatic artery, portal vein, inferior vena cava, and hepatic veins) were identified. These
same areas were then evaluated on the angiographic sequences. The brightness vessel
of the signal within the vessels and the sharpness
of the
walls were evaluated. Respiratory or motion artifacts, such as
blufflng of the vessels and ghosting, were noted. Visibility of the major vessels with MR angiography was graded as equal to, better than, or worse than that on the SE images. The presence of either portosystemic collateral vessels or tumor vasculanty was also determined for both MR angiographic and SE techniques.
ET AL.
AJR:159,
September 1992
nant hepatic tumors. In six examinations, lange vessels coursing through and around the tumor were seen on MR angiography only. MR angiography showed occlusion of major yes-
sels
in three
examinations.
One
of these
patients
had
preoperative arteniognaphy, which showed the same findings (Fig. i ). One patient had cavernous transformation of the portal vein caused by tumor invasion of the porta hepatis (Fig. 2).
MR angiography of patients before
was useful in two liver transplantation.
of seven examinations The MR angiogram
showed the presence of portosystemic collaterals (Fig. 3) in both cases and a replaced hepatic artery in one. MR angiography showed flow in the portal vein in all seven examinations. Images obtained after processing sity-projection algorithm were not resulted in a confusing overlap of intensity projection was occasionally contiguous slices were reformatted
with the maximum-intenbeneficial because they vessels. The maximumhelpful when only a few together. The most useful
vascular information was obtained from the axial and coronal raw data images from the MR angiognams. Respiratory and motion artifacts were present on all MR angiognaphic blurring (two
sequences and ranged from mild to severe patients) of the vessel walls. Ghosting artifacts
of the aorta were most prominent
in children
old. This was eliminated
on sequences
arterial flow. Respiratory
artifacts
dome
less than 2 years
with
presatunation
were most prominent
of
at the
of the liver.
Discussion
MR is being used increasingly in the evaluation of abdominal diseases in children [9]. Liver tumors are the third most
Results Overall,
visualization
of major
vessels
(aorta,
celiac
artery,
hepatic artery, inferior vena cava, portal vein, and hepatic veins) was better with MR angiography than with SE Sequences in 12 cases (60%), equal in five (25%), and worse in three (1 5%). In the eight studies in which the quality of vessel visualization on MR angiograms was graded equal to or worse than that on SE images, all the patients were less than i year old. Additional vascular information was obtained with MR angiography
vascular
in i 0 of 20 cases.
In two patients,
this additional
was obtained even though the overall had been rated as equal to on less than that of the SE images. One patient with hemangioendotheliomas and congestive heart failure had an MR angiogram that showed marked quality
dilatation
information
of the
MR
angiograms
of the hepatic
artery
and
hepatic
veins.
The
MR
angiogram helped to differentiate the dilated hepatic artery from the portal vein. These large vessels could not be differentiated on SE images. An abdominal arteniogram obtained before embolization of the hepatic artery confirmed the anatomy of the major vessels seen on the MR angiogram. However, arteniography also displayed collateral vessels to the tumors from the superior mesentenic artery and intercostal arteries that were not shown by MR angiognaphy. MR angiography showed surgically important vascular structures in seven of 1 0 examinations of patients with malig-
common
intnaabdominal
neoplasms
in childhood.
Approxi-
mately two thirds of these tumors are malignant. The remainden are due to vascular malformations or benign tumors [1 0]. The primary treatment of malignant hepatic neoplasms in children
is complete
surgical
resection
of the tumor.
Con-
sequently, preoperative assessment of vascular and sectional anatomy of the liver is important. Some investigators maintain that conventional angiography is still required for presurgical planning for such patients [1 1]. However, MR angiography combined with SE sequences made conventional angiography
unnecessary patient,
in all but one of the patients
an extremely
large
tumor
with
in our series. In that possible
occlusion
of
the portal vein was found in the region of the porta hepatis, and angiography did not provide any more information than MR imaging did. MR imaging can be useful in differentiating hepatic hemangiomas from other nonvascular tumors of the liven [12, 13]. Children with hemangioendotheliomas of the liver may have
congestive through
heart the
tumors.
failure
caused
Embolization
by excessive of the
hepatic
blood
flow
arteries
can
be performed
the
if drug and other therapies fail [i4]. Although combination of MR angiography and SE imaging can
show the hepatic lization, visualize
arterial and venous
anatomy
before embo-
the resolution of MR angiography is not adequate to small collateral vessels. In the one child who had
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AJR:159,
September
MR
1992
ANGIOGRAPHY
OF
LIVER
DISEASE
IN CHILDREN
619
Fig. 1.-I-year-old boy with hepatoblastoma. A, Axial Ti-weighted MR image shows large hepatoblastoma (straight arrows) in liver displacing hepatic artery (curved arrow). B, Coronal MR angiogram (maximum-intensity projection) shows occlusion of inferior vena cava (curved arrow), which refills via collaterals at hepatic veins (arrowhead). Large collateral vein (open arrow) on surface of tumor and multiple small collaterals (straight solid arrows) course around periphery of mass. C, Axial TI-weighted MR image obtained after 6 months of chemotherapy shows clot or slow flow in inferior vena cava (arrowhead). Note tortuous vessel (large arrow) parallel to portal vein (small arrow). D, Axial MR angiogram shows flow in inferior vena cava (open arrow) and portal vein (straight solid arrow). Tortuous vessel (curved arrow) Is a collateral vein connecting portal vein and superior mesenteric vein. E, Axial MR angiogram shows occlusion of right portal vein (curved arrow) by tumor (straight arrows). F, Late phase of superior mesenteric digital angiogram confirms occlusion of right portal vein (curved arrow) and presence of a collateral vein (straight arrow) connecting superior mesenteric vein and portal vein.
arteniography before embolization, systemic collateral vessels from the superior mesenteric and intercostal arteries were
onstration
detected that were not seen on MR angiograms or SE images. Conventional angiography is still required to plan embolization procedures in these children.
lies are common (1 4%) [20]. In children with extrahepatic biliany atresia, detection of a preduodenal portal vein or azygous continuation of the inferior vena cava before surgery is
Sonognaphy
remains
the primary
method
liver and its vasculatune
before
[i5]. Early angiography
work [1 6] has in the examination
investigational can be useful
liver disease
for evaluating
transplantation
the
in children
shown that MR of patients with
and portal hypertension. MR angiography is portal vein thrombosis, vanices [i 7], and dynamic flow within the portal system [i 8]. Demonstration of portal vein patency and vanices is important, as is the demaccurate
in showing
with
of normal
liven disease,
important.
vascular
hepatobiliary
Although
these
anatomy and
vascular
other
[1 5, 19]. In children congenital
anomalies
are
considered a contraindication to transplantation, of these variants allows preoperative planning grafts [21]. In two
of our examinations,
portosystemic
anoma-
no longer
knowledge of vascular
collateral
vessels
and
subcuta-
(short
gastric,
coronary,
gastroesophageal,
neous These
vanices) vessels
were displayed only on MR were not observed on previous
angiognaphy. sonognams.
HUBBARD
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620
ET AL.
AJR:159,
September
1992
Fig. 2.-6-year-old boy with hepatocellular carcinoma, after 6 months of chemotherapy. A, Axial MR angiogram shows cavernous transformation of portal vein (straight arrow) caused by tumor in perth hepatis (curved arrows). B, Coronal MR angiogram (maximum-intensity projection) also shows cavernous transformation (arrow) of occluded portal vein.
Fig. 3.-2-year-old drome and liver failure
boy with short-gut syncaused by chronic hyper-
alimentation. A, Axial Ti-weighted MR image shows dilatation (arrow) of splenic vein. B, Axial MR anglogram shows dilated tortuous splenic vein (open arrow) with portosystemic (lqrge solld arrows) and cutaneous collateral (small solid arrows) vessels not seen on SE images.
Vanices associated with portal hypertension may be difficult to see on sonograms because of overlying bowel gas. Bowel gas did not obscure the portal on mesenteric anatomy on MR angiograms in any of our patients. Preoperative knowledge of the existence of such collatenals in patients with portal hypertension or large tumor vessels in patients with neoplasms enables more careful surgical dissection. Respiratory artifacts on the MR angiognaphic images were most prominent in children less than i year old. This probably reflects the higher respiratory rate of young children. Motion
mation, superior
artifacts
patic vasculatune in children respiration will also improve.
on MR angiognaphy
dome, causing blurring of junction. This area of the images. Ghosting artifacts were also most prominent can be eliminated by using The method used in our grams
and SE images
was
were
most
prominent
at the liver
the hepatic veins and cavoatnial liven was seen better on the SE from pulsatile flow in the aorta in younger children. This artifact presaturation of arterial flow. study to compare the MR angionot blinded,
and,
collateral vessels seen on MR angiognams were not identified, on SE images. Although sagittal
in this study,
they may provide
regarding the origins of the celiac and arteries. In conclusion, although artifacts caused by respiratory motion were present on many of our MR angiognaphic images, these artifacts did not interfere with the diagnostic usefulness of the examinations. Additional vascular information was obtamed with MR angiography in 50% of cases. As shorter TRs and TEs lead to faster imaging techniques, and as methods for motion compensation, gradient-moment nulling, and
phase-encoded
reordering
improve, who
the demonstration are
unable
of he-
to
suspend
and
academic
AJR
1990:155:
ACKNOWLEDGMENTS We thank
support
Ken
Fellows
for editorial
suggestions
and Valerie Tsafos for secretarial
help.
consequently,
some bias may have been introduced. The method of grading the quality of images was quite subjective. Nonetheless,
not obtained
particularly mesentenic
sought, but scans were
additional
infon-
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AJR:159,
September
1992
MR
ANGIOGRAPHY
OF
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consideratransplansyndrome: