AJR 2003; 181:861-866
© American Roentgen Ray Society
Contrast-Enhanced MR Angiography of Thoracic Vascular Malformations in a Pediatric Population
Filipe Caseiro-Alves1,2,
Paulo Gil-Agostinho1,
Graça Ramalheiro3 and
Pedro Gil-Agostinho1
1 Imacentro, Clinica de Imagiologia Médica, Rua S.Teotónio, Lote
8, 5° Esq., 3000-377 Coimbra, Portugal.
2 Faculdade de Medicina de Coimbra, Cadeira de Imagiologia, 3000-075 Coimbra,
Portugal.
3 Paediatric Cardiology Department, Hospital Pediátrico de Coimbra, Av.
Bissaia Barreto, 3000 Coimbra, Portugal.
Received December 5, 2002;
accepted after revision January 28, 2003.
Address correspondence to F. Caseiro-Alves
(fcalves{at}netcabo.pt).
Introduction
Diagnostic gadolinium-enhanced MR angiography has been successfully used in
the past few years for a vast array of medical indications
[1]. With the new
high-performance gradients that allow the use of an ultrashort TR and TE,
three-dimensional (3D) data sets can now be acquired in a single breath-hold.
Also, the new schemes for k-space reconstruction, such as the centric or
elliptic-centric modes, ensure the most useful phase of reduced blood
T1-weighted relaxation is easily captured, increasing the temporal resolution
necessary to image both arterial and venous structures
[1,
2].
Performing contrast-enhanced MR angiography in pediatric patients,
particularly neonates, poses additional problems because examinations are
typically conducted with the patient under general anesthesia in a
non-breath-hold fashion. Previous reports have shown the feasibility of using
contrast-enhanced MR angiography in a pediatric population to study several
vascular thoracic and abdominal abnormalities, mainly of the arterial system
[2-5].
In addition, the ability to study malformations of the thoracic vasculature in
neonates under general anesthesia and during spontaneous breathing has been
described (Caseiro-Alves F et al., presented at the Radiological Society of
North America meeting, December 2000). Our imaging group is working closely
with a national referral center for pediatric cardiology and has already
performed more than 100 of these procedures. All patients were examined with
light anesthesia produced by inhalation of sevoflurane (Ultane, Abbott
Laboratories, Amadora, Portugal). To date, no cases of severe adverse effects
have been registered, even when imaging 1-day-old neonates with complex
cyanotic congenital cardiopathy and blood oxygen saturation levels as low as
40-50%.
Technique
Images were generated in two magnetic fields (1 and 1.5 T) (Signa Horizon
and Signa MRI EchoSpeed Plus, General Electric Medical Systems, Milwaukee,
WI). A 3D fast gradient-echo sequence was performed in the coronal plane using
a nominal slice thickness of 3.2 mm and a partition number selected depending
on the anatomic area to cover. The choice of imaging coil depended on the size
of the patient; the head transmitting-receiver coil was regularly used in
infants who weighed less than 9 kg. The 3D sequence was acquired in 18-20 sec.
It was launched after a fixed delay of 15 sec after the manual injection of a
double dose (0.2 mmol/kg of body weight) of IV ionic gadopentetate dimeglumine
(Magnevist, Schering, Berlin), and the contrast-generating k-space central
lines were acquired during the first few seconds. The complete procedure
including administration of anesthesia was concluded in approximately 10-15
min. Interpolated reconstruction was regularly applied to obtain a final
number of slices multiplied by a factor of 2 or 4 without any penalty in
acquisition time.
The native coronal two-dimensional slices (typically 80-120 images) were
transferred to a diagnostic workstation (Advantage Windows 4.0, General
Electric Medical Systems) for 3D postprocessing using
maximum-intensity-projection and volume-rendering techniques.
Clinical Results
Corroborating the findings of previous reports that focused mainly on the
arterial thoracic vessels
[6-8],
this pictorial essay shows the potential uses of contrast-enhanced MR
angiography for the diagnosis of vascular thoracic malformations in both the
arterial and venous systems in pediatric patients. These uses make the
technique a valuable diagnostic tool with the potential to replace the more
invasive digital subtraction angiography.
Aortic Arch Anomalies
Aortic Coarctation
Aortic coarctation (Figs.
1A,
1B, and
1C) is a narrowing of the
aortic arch generally at the level of the ductus arteriosus. This anomaly can
be diffuse, causing tubular hypoplasia of the aortic arch (the infantile
type), or segmental (the adult type).
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Fig. 1A. —Spectrum of findings in selected cases of aortic coarctation
(arrowhead, A and B) shown on contrast-enhanced MR
angiograms obtained using three-dimensional techniques. Parasagittal oblique
maximum-intensity-projection image of 2-day-old female neonate shows simple
isolated coarctation at its typical location.
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Fig. 1B. —Spectrum of findings in selected cases of aortic coarctation
(arrowhead, A and B) shown on contrast-enhanced MR
angiograms obtained using three-dimensional techniques.
Maximum-intensity-projection image of 1-year-old male infant displays
collaterals (intercostals) developed for arterial circulation.
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Fig. 1C. —Spectrum of findings in selected cases of aortic coarctation
(arrowhead, A and B) shown on contrast-enhanced MR
angiograms obtained using three-dimensional techniques. Posterior oblique
volume-rendered image of 28-day-old male neonate shows severe coarctation
associated with hypoplastic distal aortic arch.
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Aortic Arch Interruption
Aortic arch interruption (Fig.
2) is a complete separation of the ascending and descending
segments of the thoracic aorta. According to Weinberg
[8], aortic arch interruption
can be classified as type A, when the interruption is distal to the left
subclavian artery origin; type B, when between the carotid and left subclavian
arteries; or type C, when located in the proximal aortic arch between the
carotid arteries.
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Fig. 2. —2-day-old male neonate with aortic arch interruption.
Contrast-enhanced three-dimensional MR angiogram obtained using
volume-rendering technique reveals type A interruption of aortic arch
(arrow). Arrowhead = left subclavian artery.
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Double Aortic Arch
Double aortic arch (Figs.
3A, and
3B) corresponds to the
persistence of both fetal aortic arches and has several variants: both arches
may be widely patent or one of the two arches may became hypoplastic or even
atretic (usually the one on the left side). The trachea and esophagus may be
completely surrounded by the aortic arches, which results in a vascular ring.
Because some degree of tracheomalacia is usually associated with this
condition, clinical signs associated with vascular compression such as stridor
or vomiting may be present.
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Fig. 3A. —Contrast-enhanced three-dimensional MR angiograms reveal
double aortic arch (arrows) that gave rise to stridor in 75-day-old
male infant. Coronal oblique maximum-intensity-projection image shows early
bifurcation of ascending aorta.
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Fig. 3B. —Contrast-enhanced three-dimensional MR angiograms reveal
double aortic arch (arrows) that gave rise to stridor in 75-day-old
male infant. Superior volume-rendered image shows double aortic arch.
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Aberrant Right Subclavian Artery
An aberrant right subclavian artery
(Fig. 4) can give rise to the
clinical sign of dysphagia lusoria. In patients with this malformation, the
right subclavian artery (arteria lusoria) crosses the superior mediastinum
behind the esophagus and potentially causes compression over its posterior
wall.
Right Aortic Arch with Retroesophageal Kommerell Diverticulum
In patients with this malformation, the aortic arch has a right-sided
configuration and the first emerging branch is the left carotid artery. A
retroesophageal vessel of variable size (the so-called Kommerell diverticulum)
gives rise to the left subclavian artery
(Fig. 5). This abnormal pouch
of variable length corresponds to the atretic portion of the left fetal arch
and is connected to the left ductus arteriosus or ligamentum arteriosum. This
vessel arrangement may also behave as a vascular ring that produces
dysphagia.
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Fig. 5. —Posterior contrast-enhanced three-dimensional MR angiogram
obtained using volume-rendering technique shows incomplete double aortic arch
forming retroesophageal Kommerell diverticulum (arrowhead) in
35-day-old male infant. Left subclavian artery (arrow) can be seen
arising in "diverticular" component of vascular ring.
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Right Aortic Arch with Mirror Image of the Supraaortic Vessels
As the name implies, the vessels are arranged as a mirror image of the left
aortic arch (Figs. 6A, and
6B). This condition is one of
the most common aortic arch abnormalities and is frequently associated with
other congenital cardiopathy.
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Fig. 6A. —Contrast-enhanced three-dimensional MR angiograms obtained
using volume-rendering technique show right aortic arch with mirror image of
supraaortic vessels in 12-day-old female neonate with dextrocardia. Anterior
(A) and posterior (B) images show right aortic arch with mirror
image of supraaortic vessels and also reveal double superior vena cava:
straight arrow points to left superior vena cava; arrowhead, to right superior
vena cava; and curved arrow, to left brachiocephalic trunk.
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Fig. 6B. —Contrast-enhanced three-dimensional MR angiograms obtained
using volume-rendering technique show right aortic arch with mirror image of
supraaortic vessels in 12-day-old female neonate with dextrocardia. Anterior
(A) and posterior (B) images show right aortic arch with mirror
image of supraaortic vessels and also reveal double superior vena cava:
straight arrow points to left superior vena cava; arrowhead, to right superior
vena cava; and curved arrow, to left brachiocephalic trunk.
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Abnormalities of the Pulmonary Arteries
There is a broad spectrum of possible congenital malformations of the
pulmonary trunk and major vessels, ranging from isolated stenosis to severe
hypoplasia or even atresia. In addition to revealing the presence or absence
of the major pulmonary trunk and branches, contrast-enhanced MR angiography
allows the direct measurement of the diameter of these pulmonary vessels
(Fig. 7). These measurements
are important in determining whether a surgical shunt (e.g., Blalock-Taussig
shunt) can be created to correct the malformation because creating this shunt
may not be feasible if the pulmonary arteries measure less than 3 mm.
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Fig. 7. —1-day-old male neonate with hypoplasia of pulmonary artery
branches. Contrast-enhanced three-dimensional MR angiogram obtained using
volume-rendering technique allows diameter of vessel to be measured. Dotted
line corresponds to diameter measurement of left pulmonary artery (2.6 mm). AA
= ascending aorta, LA = left atrium, arrowhead = left pulmonary artery.
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Abnormal Venous Connections
Pulmonary
Abnormal pulmonary venous connections can be divided into partial abnormal
venous return, such as that seen in patients with scimitar syndrome
(Fig. 8), and total abnormal
venous return. The latter category can be further subdivided: the supracardiac
type, in which a vertical vein draining the common pulmonary veins joins the
left innominate vein to open into the superior vena cava (Figs.
9A and
9B); the infracardiac type, in
which the pulmonary veins drain directly into the coronary sinus; the common
type, in which the pulmonary veins drain into the right atrium; and the rare
infradiaphragmatic type, in which the pulmonary veins join in a common trunk
to drain into the portal vein (Fig.
9C).
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Fig. 8. —3-year-old boy with partial abnormal pulmonary venous return.
Anterior contrast-enhanced three-dimensional MR angiogram obtained using
maximum-intensity-projection technique reveals connection of right pulmonary
vein to inferior vena cava (arrow), indicating scimitar syndrome.
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Fig. 9A. —Two types of total abnormal pulmonary venous return shown on
contrast-enhanced three-dimensional MR angiography. Coronal image of 1-day-old
male neonate reveals supracardiac type of total abnormal pulmonary venous
return: common vertical vein (arrow) drains all pulmonary veins.
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Fig. 9B. —Two types of total abnormal pulmonary venous return shown on
contrast-enhanced three-dimensional MR angiography. Volume-rendered image of
same patient as shown in A reveals connection of pulmonary veins
(arrowheads) to common vertical vein (arrow) better than
A.
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Fig. 9C. —Two types of total abnormal pulmonary venous return shown on
contrast-enhanced three-dimensional MR angiography. Coronal image of 3-day-old
male neonate with infracardiac type of total abnormal venous return shows
pulmonary veins converge toward single abnormal channel (arrowhead)
that crosses mediastinum to drain into left portal vein (arrow).
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Systemic
These conditions are variants of the normal systemic venous drainage and do
not produce clinical symptoms or signs. The most common variant is a
persistent left superior vena cava connecting either to the right atrium in
92% of cases (Figs. 10A, and
10B) or to the left atrium in
the remaining cases. The depiction of a persistent left superior vena cava may
influence the choice of the side on which to perform a surgical
pulmonary-systemic shunt.
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Fig. 10A. —2-year-old boy with abnormal systemic venous connection shown
on contrast-enhanced three-dimensional MR angiography. Lateral
maximum-intensity-projection image (A) and anterior volume-rendered
image (B) show persistent left superior vena cava (arrow)
connects to coronary sinus (arrowhead, A).
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Fig. 10B. —2-year-old boy with abnormal systemic venous connection shown
on contrast-enhanced three-dimensional MR angiography. Lateral
maximum-intensity-projection image (A) and anterior volume-rendered
image (B) show persistent left superior vena cava (arrow)
connects to coronary sinus (arrowhead, A).
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Follow-Up for Corrected Vascular Abnormalities
Contrast-enhanced MR angiography can also be useful for the evaluation of
patients who have undergone surgery to correct a vascular abnormality.
Although surgically created shunts are small, contrast-enhanced MR angiography
can reveal whether the shunt is patent, as we have observed in patients with
Blalock-Taussig shunts (Figs.
11A, and
11B). In addition, the
postsurgical status of a surgically corrected aortic coarctation can be
monitored by obtaining direct measurements of the vessel diameter
(Fig. 12).
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Fig. 11A. —Contrast-enhanced MR angiograms obtained at postsurgical
follow-up of 3-year-old girl who underwent placement of modified
Blalock-Taussig shunt. Posterior volume-rendered image (A) and coronal
maximum-intensity-projection image (B) show patency of modified
Blalock-Taussig shunt (arrow).
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Fig. 11B. —Contrast-enhanced MR angiograms obtained at postsurgical
follow-up of 3-year-old girl who underwent placement of modified
Blalock-Taussig shunt. Posterior volume-rendered image (A) and coronal
maximum-intensity-projection image (B) show patency of modified
Blalock-Taussig shunt (arrow).
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Fig. 12. —4-year-old boy in whom recoarctation of aorta was suspected
on basis of findings on Doppler sonograms (not shown) that revealed 15-mm-Hg
systolic pressure gradient between two segments of aorta. This posterior
oblique contrast-enhanced MR angiogram obtained using volume-rendering
technique was used to calculate aortic diameter.
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