AJR 2001; 177:1045-1049
© American Roentgen Ray Society
Using Electron Beam CT to Evaluate Conotruncal Anomalies in Pediatric and Adult Patients
Byoung Wook Choi1,
Young Hwan Park2,
Jae Young Choi3,
Byung In Choi1,
Min Jung Kim1,
Seok Jong Ryu1,
Jong Kyun Lee3,
Jun Hee Sul3,
Sung Kyu Lee3,
Bum Koo Cho2 and
Kyu Ok Choe1
1
Department of Diagnostic Radiology, Research Institute of Radiological
Science, Yonsei University College of Medicine, 134 Sinchon-dong,
Seodaemoon-gu, Seoul 120-752, Korea.
2
Division of Cardiovascular Surgery, Yonsei University College of Medicine,
Seoul 120-752, Korea.
3
Division of Pediatric Cardiology, Yonsei University College of Medicine, Seoul
120-752, Korea.
Received November 30, 2000;
accepted after revision May 1, 2001.
Address correspondence to K. O. Choe.
Introduction
Electron beam CT has advantages over echocardiography and MR imaging in
evaluating congenital cardiac malformations. These advantages include short
scanning time (50-400 msec), high temporal and spatial resolution, and
compatibility with ECG gating. Electron beam CT can clearly delineate the
cardiac chambers and the vessels in the mediastinum and chest wall. The
technique is particularly useful in young children without a need for deep
sedation.
Pressure measurement of the cardiac chambers is not possible using electron
beam CT, but it is rarely a critical issue in conotruncal anomalies. The
pressures in the right and left ventricles and in the aorta are frequently
equal as a result of a commonly associated large ventricular septal defect,
pulmonic stenosis, or both, and because the pulmonary blood flow is usually
normal or slightly diminished in conotruncal anomalies. On the other hand,
anatomic information that is obtainable by electron beam CT, such as the
dimensions of the pulmonary artery and the presence of infundibular stenosis
or coronary anomalies, is essential in planning surgical correction of these
anomalies
[1,2,3,4].
This pictorial essay illustrates the value of electron beam CT in assessing a
variety of conotruncal anomalies.
Overview of Technique
The technique used in electron beam CT includes single-slice mode with ECG
gating at the end-systolic phase and at diastasis (40% and 80% R-R interval,
respectively); field of view, 12 x 15 cm; slice thickness, 1-3 mm;
interslice interval, 0; nonionic iodinated IV contrast material, iopamidol
(Iopamiro 370; Bracco, Milano, Italy) at 2.0 mL/kg body weight and injection
rate of 0.3 mL/sec; scan delay, 10 sec.
In general, the systolic images are better for evaluating the great
vessels, whereas the diastolic images better delineate the ventricular detail.
Comparison of systolic and diastolic images can provide rough ideas of
function, such as ventricular ejection fraction or wall motion. The two sets
of data in the systolic and diastolic phases can offer good quality
three-dimensional reconstructed images. The protocol is tailored to the
requirements of each patient. Flow mode, cine mode, and thin-section CT of the
lung are performed in some patients, primarily for functional information.
Uses of Electron Beam CT
Sequential Chamber Localization
Sequential chamber localization is a fundamental step in the diagnosis of
conotruncal anomalies. Accurate characterization of the cardiac chambers and
the great vessels is essential for the evaluation of atrioventricular and
ventriculoarterial concordance or discordance (Figs.
1A,1B
and
2A,2B,2C).
The criteria for the recognition of morphologic right ventricle include coarse
trabeculation, presence of a moderator band, and more apical insertion of the
tricuspid valve than of the contralateral valve in the body of the right
ventricle. On the other hand, the morphologic left ventricle is recognized by
its fine trabeculation and less apical insertion of the atrioventricular valve
(mitral valve) to the septum than to the contralateral side (Figs.
1B and
2C). The aortic arch and the
takeoff of the coronary arteries permit recognition of the aorta.
Identification of the short trunk and the immediate bifurcation is the key to
recognizing the main pulmonary artery (Figs.
1A and
2B).
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Fig. 1A. —17-year-old boy with corrected transposition of great
vessels. Electron beam CT scan at level of great arteries shows aorta (A)
anterior to and left of pulmonary artery (P), which is dilated because of
left-to-right shunt and pulmonary arterial hypertension. Note bilateral
superior vena cavae (arrows); left superior vena cava is more faintly
opacified because contrast material was injected in vein of right arm.
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Fig. 1B. —17-year-old boy with corrected transposition of great
vessels. Electron beam CT scan at level of atrioventricular valves shows
left-sided ventricle with coarser trabeculation and more apical insertion of
atrioventricular valve (arrowheads) than that seen in contralateral
ventricle (arrows). Note moderator band (M) near apex, creating
morphologic right ventricle. Morphologic right ventricle is hypertrophied
because it works as systemic ventricle. In combination with more cephalad
section seen in A, main pulmonary artery arises from morphologic left
ventricle, whereas aorta arises from morphologic right ventricle, representing
ventriculoarterial discordance. CS = coronary sinus.
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Fig. 2B. —2-month-old girl with complete transposition of great
vessels. Electron beam CT scan at level slightly lower than semilunar valves
shows aorta (A) arising from right ventricle, and pulmonary artery (P) arising
from left ventricle. Infundibulum of right ventricle connected to aorta
reveals muscular thickening and narrowing of subaortic outflow tract of right
ventricle (arrows). RA = right atrium, LA = left atrium, LV = left
ventricle.
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Fig. 2C. —2-month-old girl with complete transposition of great
vessels. Electron beam CT scan at level of atrioventricular valves shows valve
insertion is less apical in left-sided ventricle (arrowheads) than
contralateral side (thin arrows), indicating left-sided ventricle is
morphologic left ventricle (LV). Atrioventricular concordance and
ventriculoarterial discordance lead to diagnosis of complete transposition of
great vessels. Note small atrial septal defect (thick arrow).
Thickness of myocardial wall is similar in left and right ventricles. LA =
left atrium, RV = right ventricle.
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Complete Transposition of Great Vessels
The diagnostic criterion of complete transposition of great vessels is a
discordant ventriculoarterial connection (Fig.
2A,2B,2C).
The preferred corrective repair is an arterial switch operation, in which the
left ventricle serves as a systemic ventricle. An estimate of the left
ventricular mass and detailed images of the anatomy of the coronary arteries
are crucial in planning corrective surgery that can be obtained using electron
beam CT. In the case of a complete transposition of great vessels without a
ventricular septal defect, the pulmonary artery pressure falls immediately
after birth, resulting in myocardial thinning of the left ventricle
(Fig. 3). In such cases, the
arterial switch operation should be done within the patient's first 2 weeks of
life. In complete transposition of great vessels with ventricular septal
defect, myocardial thinning of the left ventricle may be delayed because its
pressure is equal to that of the right ventricle. The main problem in this
case may be the obstruction of the left ventricular outflow tract.
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Fig. 3. —1-year-old boy with complete transposition of great vessels
and no ventricular septal defect. Electron beam CT scan shows cardiac apex on
right and cardiac situs solitus. Note thinness of left ventricular wall
(arrows). LV = left ventricle, RV = right ventricle.
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Corrected Transposition of the Great Vessels
Corrected transposition of the great vessels is defined by discordant
atrioventricular and ventriculoarterial connections (Figs.
1A,1B
and
4A,4B).
Ventricular septal defect and pulmonary stenosis are frequently associated
with this anomaly. Conduction tissue runs anterior to the normal pathway
because of malaligned atrial and ventricular septa. If atrioventricular
discordance is present, a specialized technique is used to avoid injury to the
conduction tissue during repair of the ventricular septal defect or while
performing a Rastelli operation for repair of infundibular pulmonary
stenosis.
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Fig. 4A. —27-year-old man with corrected transposition of great
vessels. Frontal view three-dimensional image reconstructed from electron beam
CT scans shows ventriculoarterial discordance and relationship of great
arteries. Note aorta (A) arising from morphologic right ventricle (RV), and
pulmonary artery (P) arising from morphologic left ventricle (LV).
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Fig. 4B. —27-year-old man with corrected transposition of great
vessels. Oblique view three-dimensional image reconstructed from electron beam
CT scans shows anterosuperior recess (arrowheads) of morphologic left
ventricle (LV), which is caused by posterior location of discordant pulmonary
artery (P) and anterior location of left ventricular outflow tract. A =
aorta.
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Tetralogy of Fallot
Anterior displacement of the infundibular septum is the fundamental
anatomic defect in tetralogy of Fallot (Fig.
5A,5B,5C,5D).
This displacement results in a malaligned ventricular septal defect just below
the aortic valve, infundibular pulmonary stenosis, and an overriding of the
aorta. Right ventricular hypertrophy follows as a result of pressure overload.
The preoperative requisites for total correction include sufficient
development of the pulmonary artery (Fig.
5A), absence of the coronary artery that crosses over the right
ventricular outflow tract (Fig.
5B), and sufficient end-diastolic volume of the left ventricle
(Fig. 5D). If these requisites
are not satisfied, a shunt operation should be performed initially and
corrective surgery undertaken after pulmonary artery dimensions and left
ventricular volume have reached sufficient size. The Rastelli operation should
be considered when the coronary artery crosses over the right ventricular
outflow tract [5].
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Fig. 5A. —27-year-old man with tetralogy of Fallot. Electron beam CT
scan at level of great arteries shows stenosis (arrows) at junction
of main (M) and right (R) pulmonary arteries. L = left pulmonary artery, A =
aorta.
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Fig. 5B. —27-year-old man with tetralogy of Fallot. Electron beam CT
scan at level of aortic root shows normal relationship of great arteries,
dilated aortic root (A), normal coronary artery pattern, and dilated right
coronary artery (RCA) supplying hypertrophied right ventricle. P = pulmonary
artery, arrows = left anterior descending coronary artery, arrowheads = left
circumflex coronary artery, LA = left atrium.
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Fig. 5C. —27-year-old man with tetralogy of Fallot. Electron beam CT
scan shows hypertrophied right ventricle (RV), less than 50% overriding of
aorta, and large subaortic ventricular septal defect (large arrow).
Note noncoronary cusp of aortic valve seen as thin line (small
arrow). RA = right atrium, LA = left atrium, LV = left ventricle.
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Fig. 5D. —27-year-old man with tetralogy of Fallot. Electron beam CT
scan in diastolic phase shows right ventricular (RV) hypertrophy and
sufficient end-diastolic volume of left ventricle (LV), which is major concern
in surgical repair of tetralogy of Fallot.
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Double-Outlet Right Ventricle
Double-outlet right ventricle is a group of heterogeneous diseases (Figs.
6A,6B,6C,7,8)
in which both the aorta and the pulmonary arteries are connected to the right
ventricle [6]. The selection of
the operative method depends on the type of ventricular septal defect relative
to the great arteries. Subaortic ventricular septal defect is the easiest type
to repair by intracardiac baffle. In subpulmonic or doubly committed
ventricular septal defect, the Rastelli operation,
Réparation
á l'étage
ventriculaire, or the arterial switch procedure should be considered if
the space between the tricuspid valve and pulmonary valve is insufficient
(Fig. 6C). In noncommitted
ventricular septal defect, repair is the same as in single ventricle.
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Fig. 6A. —6-year-old boy with double-outlet right ventricle and
subpulmonary ventricular septal defect. Electron beam CT scan shows aorta (A)
anterior to pulmonary artery (P). S = superior vena cava.
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Fig. 6B. —6-year-old boy with double-outlet right ventricle and
subpulmonary ventricular septal defect. Electron beam CT scan shows aorta (A)
and pulmonary artery (P) arising from right ventricle (RV). LV = left
ventricle, RA = right atrium.
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Fig. 6C. —6-year-old boy with double-outlet right ventricle and
subpulmonary ventricular septal defect. Electron beam CT scan shows large
subpulmonary ventricular septal defect (large arrow) and infundibular
septum (IS) between subpulmonic and subaortic infundibula. Subpulmonic
infundibulum is stenotic (small arrow). RV = right ventricle, RA =
right atrium, A = aorta.
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Fig. 7. —1-year-old boy with subpulmonic ventricular septal defect
(not shown) and double-outlet right ventricle. Three-dimensional image of
electron beam CT scans with slight right anterior oblique view reveals two
great arteries arising from right ventricle (RV), distinguished by coarser
trabeculation from left ventricle (LV). Note interventricular septum
(arrows). A = aorta, P = main pulmonary artery.
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Fig. 8. —3-month-old infant with double-outlet right ventricle and
subaortic ventricular septal defect. Three-dimensional image of electron beam
CT scans with posterior and bottom-up view shows subaortic ventricular septal
defect (arrow). A = aorta, P = main pulmonary artery, S =
interventricular septum, LV = left ventricle, RV = right ventricle.
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Other Uses
Compared with echocardiography, electron beam CT has a wider field of view,
making it a better tool to evaluate peripheral pulmonary stenosis (Fig.
9A,9B,9C).
The extent of interruption of the pulmonary artery and the dimension of the
hilar pulmonary artery distal to the interruption can be measured accurately
only by electron beam CT (Fig.
10A,10B,10C).
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Fig. 9A. —10-month-old infant with peripheral stenosis of pulmonary
artery and double-outlet right ventricle having ventricular septal defect and
other anomalies. Pulmonary arteriogram shows stenosis (arrow) of left
pulmonary artery (L) and dilatation of main pulmonary artery (M).
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Fig. 9B. —10-month-old infant with peripheral stenosis of pulmonary
artery and double-outlet right ventricle having ventricular septal defect and
other anomalies. Electron beam CT scan shows junctional stenosis
(arrows) between main (M) and left (L) pulmonary artery,
corresponding to finding in A.
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Fig. 9C. —10-month-old infant with peripheral stenosis of pulmonary
artery and double-outlet right ventricle having ventricular septal defect and
other anomalies. Electron beam CT scan with lung window setting at level of
carina shows decreased attenuation and fewer vessels at periphery on left lung
compared with right. Mild degree of pulmonary hypoplasia is also present.
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Fig. 10A. —17-year-old boy with tetralogy of Fallot with interruption of
left pulmonary artery. Electron beam CT scan shows interruption of left
pulmonary artery and collateral development of bronchial arteries
(arrows) in mediastinum and along left bronchial wall. L = hilar left
pulmonary artery, M = main pulmonary artery, A = aorta, R = right pulmonary
artery.
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Fig. 10B. —17-year-old boy with tetralogy of Fallot with interruption of
left pulmonary artery. Three-dimensional image of electron beam CT scans
provides exact nature of interrupted segment and gap (solid arrows)
between main and hilar left pulmonary artery. Exact measurement of oblique
course of interruption can be obtained on three-dimensional image. A = aorta,
M = main pulmonary artery, L = hilar left pulmonary artery, RV = right
ventricle, LV = left ventricle, open arrows = right coronary artery.
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Fig. 10C. —17-year-old boy with tetralogy of Fallot with interruption of
left pulmonary artery. Electron beam CT scan with lung window setting shows
decreased volume of left lung and multiple subpleural collaterals
(arrows). Mediastinal windows not shown revealed dilated intercostal
arteries in chest wall.
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Another advantage of electron beam CT over echocardiography is that
electron beam CT can provide images of lung parenchymal structures, making
possible an estimate of the status of pulmonary microcirculation. The
dimension of pulmonary vessels is related to pulmonary blood flow and
pulmonary vascular resistance
[7]. The background attenuation
of the lung parenchyma may serve as a rough estimate of capillary blood volume
[8]. Pulmonary blood flow in a
conotruncal anomaly is usually diminished (Figs.
9C and
10C).
Finally, electron beam CT can reveal the development of systemic artery
collaterals in the chest wall and mediastinum (Figs.
10B and
10C). Embolization of highly
developed systemic collateral arteries may be necessary to decrease the venous
return during the cardiopulmonary bypass. In cyanotic congenital heart
diseases with increased pulmonary blood flow, early development of
irreversible pulmonary hypertension becomes more likely
[6].
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Introduction
Overview of Technique
