AJR 2004; 182:1333-1339
© American Roentgen Ray Society
Coarctation of the Aorta Before and After Correction: The Role of Cardiovascular MRI
Eli Konen1,2,
Naeem Merchant1,
Yves Provost1,
Peter R. McLaughlin3,
Jane Crossin1 and
Narinder S. Paul1
1 Department of Diagnostic Imaging, Mount Sinai Hospital and the University
Health Network, 600 University Ave., Toronto, ON M5G 1X5, Canada.
2 Present address: Department of Diagnostic Imaging, Chaim Sheba Medical Center,
Tel Hashomer 52621, Israel.
3 Division of Cardiology, Congenital Cardiac Centre for Adults, University of
Toronto, University Health Network, Toronto, ON, Canada.
Received June 13, 2003;
accepted after revision September 23, 2003.
Address correspondence to E. Konen
(konen{at}zahav.net.il).
Introduction
Coarctation of the aorta accounts for approximately 5% of all congenital
heart disease [1] and is
defined as a congenital narrowing of the aorta. The narrowing is most commonly
located just distal to the origin of the left subclavian artery.
Traditionally, coarctations were classified into infantile (preductal) and
adult (postductal) types; however, this classification is often misleading
because age of presentation was found to be related more to the degree of
narrowing and the presence of associated abnormalities than to the location
[1]. The term "simple
aortic coarctation" refers to an isolated abnormality in the absence of
any other cardiovascular lesions. Most native (unrepaired) coarctations
detected in adults are simple. The term "complex aortic
coarctation" is used to describe a coarctation in the presence of other
important intracardiac anomalies that are usually detected in infancy.
Angiography was traditionally used as the technique of choice in the
evaluation of aortic coarctation and its postoperative complications. However,
the recent introduction of new MRI techniques enables an excellent anatomic
and functional assessment of aortic abnormalities and the evaluation of
associated additional cardiac and vascular anomalies.
Scanning Technique
All MRI examinations shown in this article were performed with a 1.5-T MR
imager (CV/i, General Electric Medical Systems) using a dedicated cardiac
coil. Scanning protocol included T1-weighted double inversion axial images
from above the aortic arch to the bottom of the heart, oblique cine MR images
using fast imaging employing steadystate acquisition throughout the aortic
valve, 3D MR angiography of the thoracic aorta, and FastCine phase-contrast
studies of the aorta obtained perpendicular to and just distal to the
coarctation, above the aortic valve, and above the diaphragm.
Evaluation of Native Coarctation and Postsurgical Recoarctation
MR angiography of the thoracic aorta, combined with postprocessed 3D
reformations, provides accurate and reproducible angiographic-like images that
enable precise measurements of the stenosis. It also shows clearly the spatial
relationship between the aortic narrowing and the origin of the major arch
vessels and the collateral vessels bypassing the stenosis
[2] (Figs.
1A,
1B,
1C,
1D and
2A,
2B,
2C,
2D,
2E). Visualization of
collateral vessels indicates the presence of a significant gradient.
Multiplanar reformations enable measurements of the maximal point of
narrowing, even in cases of complex anatomy that angiography may fail to
detect (Fig. 1A,
1B,
1C,
1D).
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Fig. 1A. —49-year-old man with native coarctation of aorta.
Volume-rendering (A) and maximal-intensity-projection (B)
reformations obtained from MR angiography delineate exact location of stenosis
(curved arrow), its spatial relationship with left subclavian artery
(asterisk), prominent and multiple collateral arteries in mediastinum
and posterior chest wall (small arrows), and large internal mammary
arteries (large arrows) bypassing coarctation.
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Fig. 1B. —49-year-old man with native coarctation of aorta.
Volume-rendering (A) and maximal-intensity-projection (B)
reformations obtained from MR angiography delineate exact location of stenosis
(curved arrow), its spatial relationship with left subclavian artery
(asterisk), prominent and multiple collateral arteries in mediastinum
and posterior chest wall (small arrows), and large internal mammary
arteries (large arrows) bypassing coarctation.
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Fig. 1C. —49-year-old man with native coarctation of aorta. Oblique
axial reformation from MR angiography along plane of maximal narrowing reveals
pinpoint (curved arrow) stenosis. Note prominent internal mammary
arteries (large arrows) and multiple mediastinal collateral vessels
(small arrows).
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Fig. 1D. —49-year-old man with native coarctation of aorta. Axial
T1-weighted double inversion recovery image obtained at level of
aortopulmonary window shows prominent intercostal (small arrows),
mediastinal (open arrows), and internal mammary (large
arrows) arteries.
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Fig. 2A. —25-year-old woman with native aortic coarctation combined
with inferior arch aneurysm and aberrant right subclavian artery. Sagittal
maximal-intensity-projection image obtained from MR angiography shows that
narrowed aortic segment (arrow) starts immediately distal to origin
of dilated left subclavian artery (asterisk) and associated inferior
bulging saccular aneurysm (dot), which most probably represents
aneurysm of ductus arteriosus stump.
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Fig. 2B. —25-year-old woman with native aortic coarctation combined
with inferior arch aneurysm and aberrant right subclavian artery. Posterior
image of volume-rendering reformation shows right aberrant subclavian artery
(arrows) arising distal to coarctation. Asterisk = dilated subclavian
artery.
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Fig. 2C. —25-year-old woman with native aortic coarctation combined
with inferior arch aneurysm and aberrant right subclavian artery.
Phase-contrast study obtained throughout neck shows retrograde flow in right
vertebral artery, indicating right subclavian steal syndrome. Magnitude image
(C on right), velocity-encoded image (C on left), and resulting
flow velocity graph (D) show opposite flow direction in right vertebral
artery (blue line) compared with left vertebral (white
line), right carotid (green line), and left carotid (red
line) arteries.
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Fig. 2D. —25-year-old woman with native aortic coarctation combined
with inferior arch aneurysm and aberrant right subclavian artery.
Phase-contrast study obtained throughout neck shows retrograde flow in right
vertebral artery, indicating right subclavian steal syndrome. Magnitude image
(C on right), velocity-encoded image (C on left), and resulting
flow velocity graph (D) show opposite flow direction in right vertebral
artery (blue line) compared with left vertebral (white
line), right carotid (green line), and left carotid (red
line) arteries.
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Fig. 2E. —25-year-old woman with native aortic coarctation combined
with inferior arch aneurysm and aberrant right subclavian artery.
Phase-contrast study was obtained throughout proximal descending thoracic
aorta just below coarctation. Both corresponding magnitude image (right) and
velocity-encoded image (left) are shown; the latter enabled computerized
analysis, which showed peak velocity of blood at that level to be almost 3
m/sec, suggesting significant pressure gradient throughout coarctation of 36
mm Hg.
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Velocity-encoded studies enable the quantification of blood flow and peak
velocities throughout the aorta and collateral vessels
[3] (Figs.
2D and
2E). Flow volumes are measured
at a level just distal to the coarctation and at the level of the diaphragm,
and the collateral flow is calculated by subtracting the proximal aortic flow
from the distal one. The presence of any positive collateral flow is
indicative of a hemodynamically significant coarctation
[4]. In addition, peak flow
velocity measurements obtained just distal to the coarctation enable the
calculation of the pressure gradient across the aortic narrowing using the
modified Bernoulli's equation: 4 x V2 =
P, where P is the pressure gradient in
millimeters of mercury and V is the measured peak velocity in meters
per second. For example, in a patient with a peak velocity of 3 m/sec, the
calculated pressure gradient would be 4 x 32 = 36 mm Hg
(Fig. 2E). A pressure gradient
greater than 20 mm Hg is suggestive of a significant aortic coarctation
[5]. Although the modified
Bernoulli's equation is used in Doppler sonography in a variety of clinical
situations, the MRI implementation of such analysis in patients with
coarctation is still not established and is a subject for further clinical
research.
Evaluation of Associated Bicuspid Aortic Valve
An associated bicuspid aortic valve is encountered in 50–85% of
patients with coarctation. This anomaly may result in aortic valve stenosis,
regurgitation, or both. Cardiac MRI allows anatomic and functional evaluation
of associated aortic valve anomalies. Cine MRI enables a confident depiction
of a bicuspid valve and a raphe, confirms the presence of thickened or
calcified leaflets, and allows a computerized measurement of the
cross-sectional area (Figs. 3A
and 3B). The normal aortic
valve orifice ranges between 2.6 and 3.5 cm2. An orifice of
1.5–2.0 cm2 is considered a mild stenosis and 1.0–1.5
cm2 as a moderate stenosis, whereas less than 0.8 cm2 is
considered a critical aortic stenosis. In addition, phase-contrast studies
acquired on an oblique axial plane just above the aortic valve allow
quantification of aortic valve regurgitation or stenosis by measuring the flow
and peak velocities near the valve (Figs.
3C and
3D).
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Fig. 3B. —44-year-old man with corrected coarctation (not shown) and
bicuspid aortic valve. Magnification of A with computerized measurement
shows increased cross-sectional area of aortic valve, 4.8 cm2.
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Fig. 3C. —44-year-old man with corrected coarctation (not shown) and
bicuspid aortic valve. Phase-contrast study was obtained in oblique axial
plane above aortic valve. Magnitude image (C on right), velocity
encoded image (C on left), and resulting graph (D) of blood flow
during single R-R interval show large systolic flow (delineated by graph below
zero line) and slower diastolic flow in opposite direction (delineated by
graph above zero line), indicating aortic valve regurgitation. Relationship
between graph areas below and above zero enables quantification of
regurgitation.
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Fig. 3D. —44-year-old man with corrected coarctation (not shown) and
bicuspid aortic valve. Phase-contrast study was obtained in oblique axial
plane above aortic valve. Magnitude image (C on right), velocity
encoded image (C on left), and resulting graph (D) of blood flow
during single R-R interval show large systolic flow (delineated by graph below
zero line) and slower diastolic flow in opposite direction (delineated by
graph above zero line), indicating aortic valve regurgitation. Relationship
between graph areas below and above zero enables quantification of
regurgitation.
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Evaluation of Associated Cardiovascular Anomalies
In addition to bicuspid aortic valve, several other anomalies have been
described in association with coarctation of the aorta. These anomalies
include a variable degree of aortic arch and isthmic hypoplasia (Fig.
4A,
4B), mitral valve
malformation, patent ductus arteriosus, ventricular septal defect, anomalous
origin of the right subclavian artery (5%) (Fig.
2A,
2B,
2C,
2D,
2E) or involvement of the left
subclavian artery in the coarctation (Fig.
5), aortic medial disease causing dilatation of the ascending and
descending thoracic aorta (Fig.
6A,
6B), and berry (intracranial)
aneurysms of the circle of Willis (3–5%). Cardiac MRI combined with
gadolinium-enhanced MR angiography enables anatomic and functional evaluation
of those associated abnormalities
[6] (Fig.
7A,
7B,
7C).
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Fig. 4A. —40-year-old man with patch correction aortoplasty for
coarctation and associated hypoplastic aortic arch. Sagittal (A) and
coronal (B) maximal-intensity-projection reformations from MR
angiography show narrowed aortic arch (large arrow, A)
measuring 8.8 x 13.5 mm and aneurysmal dilatation at level of patch
aortoplasty (small arrow, A).
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Fig. 4B. —40-year-old man with patch correction aortoplasty for
coarctation and associated hypoplastic aortic arch. Sagittal (A) and
coronal (B) maximal-intensity-projection reformations from MR
angiography show narrowed aortic arch (large arrow, A)
measuring 8.8 x 13.5 mm and aneurysmal dilatation at level of patch
aortoplasty (small arrow, A).
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Fig. 5. —45-year-old-man with native complex coarctation of aorta
(arrow) involving origin of left subclavian artery. Left common
carotid artery is missing. Maximal-intensity-projection reformation of MR
angiography shows dilated left subclavian (asterisk) and innominate
(dot) arteries. Note that only right internal mammary artery
(arrowheads) is dilated because of increased collateral flow. Left
internal mammary artery is of normal size because it originates from left
subclavian artery, which branches distal to aortic narrowing and thus does not
serve as collateral vessel. Left subclavian dilatation is presumably secondary
to poststenotic turbulence.
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Fig. 6A. —43-year-old-man with recoarctation after end-to-end repair of
aortic coarctation in childhood and associated ascending and descending
aortopathy. Right sagittal image of volume-rendering reformation from MR
angiography shows restenosis of aorta (arrow) and diffuse dilatation
of ascending (As) and descending (Ds) thoracic aorta, measuring on axial
images (not shown) 45 and 39 mm, respectively.
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Fig. 6B. —43-year-old-man with recoarctation after end-to-end repair of
aortic coarctation in childhood and associated ascending and descending
aortopathy. Cine MR image obtained throughout left ventricular outflow tract
in diastole shows dilated aortic root (between arrows) and dephasing
jet (arrowheads) through aortic valve toward left ventricle
(asterisk), indicating regurgitation.  = left atrium.
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Fig. 7A. —38-year-old-man with native complex coarctation associated
with partial anomalous pulmonary venous return and sinus atrial defect.
Sagittal maximum-intensity-projection reformation from MR angiography shows
pinpoint aortic coarctation.
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Fig. 7B. —38-year-old-man with native complex coarctation associated
with partial anomalous pulmonary venous return and sinus atrial defect.
Oblique coronal multiplanar reformations of venous phase show aberrant
pulmonary vein (PAPVR) (B) draining part of right lung into small right
superior vena cava (SVC) and associated left (Lt) persistent SVC
(C).
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Fig. 7C. —38-year-old-man with native complex coarctation associated
with partial anomalous pulmonary venous return and sinus atrial defect.
Oblique coronal multiplanar reformations of venous phase show aberrant
pulmonary vein (PAPVR) (B) draining part of right lung into small right
superior vena cava (SVC) and associated left (Lt) persistent SVC
(C).
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Evaluation of a Repaired Coarctation
A variety of surgical approaches for coarctation have been used in the last
30 years, including resection with primary end-to-end anastomosis, patch
aortoplasty with prosthetic material homograft or autologous subclavian
artery, and bypass grafting with a prosthetic tube
(Fig. 8) or autologous
vascular grafts. The most common technique in current use is resection with
end-to-end anastomosis (Fig.
9). In subclavian flap aortoplasty, the left subclavian artery is
ligated at the first branch, an incision is made along the coarctation and the
subclavian artery creating a flap, the posterior wall of the coarctation is
resected, and the subclavian flap is placed to enlarge the constricted area.
This technique is believed to allow possible growth of the anastomosis and
thus may be used in children but is not recommended in adults because of
concern about the arterial supply to the arm. Balloon dilation with stent
insertion for native aortic coarctation or recoarctation is being used
increasingly as an alternative to surgery and, in some centers, has replaced
surgery as the primary management strategy
[7]. The current stents in use
hamper MRI at the level of the stent. The follow-up of these patients can be
achieved by CT angiography, which enables a good anatomic evaluation but
without functional assessment.
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Fig. 8. —35-year-old-man with elephant trunk implantation for aortic
coarctation. Posterior image of volume-rendering reformation from MR
angiography shows interruption of distal aortic arch (Ar) and large graft (G)
connecting ascending with descending aorta (Ds). LA = left atrium, =
pulmonary veins.
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Fig. 9. —77-year-old-man with coarctation and end-to-end anastomosis
repair. Sagittal maximum-intensity-projection reformation from MR angiography
shows typical mild and nonsignificant waist at level of repair
(arrow). Phase-contrast studies (not shown) revealed normal peak
velocities at level of repair and no evidence of collateral flow. Note typical
distal origin of left subclavian artery, which was reimplanted during
surgery.
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The two most common complications after coarctation repair are late
recoarctation and aneurysm formation at the repair site. Recurrent coarctation
is more common when the coarctation is initially repaired in infancy (Fig.
6A,
6B). Aneurysm formation may
develop at the repair site or at the ascending aorta, noted in up to 5.4% of
patients who had a patch aortoplasty using Dacron (DuPont) patch material
(Fig. 4A,
4B) and usually located at the
opposite side of the patch. The risk of progressive aneurysmal dilatation and
subsequent rupture is high in cases in which the ratio between the caliber of
the dilated aorta and the diaphragmatic aorta is higher than 1:1.5
[8]. Rupture of the ascending
aorta is particularly common in association with bicuspid valve and Turner's
syndrome. Late dissection at the repair site is a rare complication but false
aneurysms may occur (Fig. 10A,
10B). Lifelong surveillance of
patients with a patch repair for the detection of aneurysm formation is
mandatory [9]. The lack of
ionizing radiation using MRI is of great advantage, especially in young
patients, who are expected to have several follow-up examinations throughout
life.
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Fig. 10A. —27-year-old-man with coarctation and tube graft repair
complicated by false aneurysm. Posterior image of volume-rendering reformation
from MR angiography shows false aneurysm arising at mid descending aorta at
distal end of graft.
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In conclusion, advanced MRI techniques allow excellent anatomic and
functional evaluation of the pre- and postsurgical aortic coarctation,
replacing angiography as the diagnostic method of choice. Angiography should
be reserved for cases in which an interventional correction procedure is
considered.
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Top
Introduction
Scanning Technique
