DOI:10.2214/AJR.04.1461
AJR 2005; 185:1007-1010
© American Roentgen Ray Society
Malignant Right Coronary Artery Anomaly Simulated by Motion Artifacts on MDCT
Marcus Katoh1,
Joachim E. Wildberger1,
Rolf W. Günther1 and
Arno Buecker1
1 Department of Diagnostic Radiology, University Hospital Aachen, University of
Technology (RWTH), Pauwelsstrasse 30, Aachen 52057, Germany.
Received September 15, 2004;
accepted after revision November 8, 2004.
Address correspondence to M. Katoh.
Abstract
OBJECTIVE. The aim of our study was to determine the prevalence of
anomalous right coronary artery imitation due to motion artifacts in MDCT.
Routine chest MDCT for reasons other than cardiac or vascular imaging is
usually performed using breath-hold technique but without retrospective ECG
gating and consequently yields pulsating motion artifacts. A possible artifact
in front of the aortic root imitates an anomalous right coronary artery
originating from the left posterior sinus. This course of the right coronary
artery is considered a malignant variant and raises the question of
far-reaching consequences such as a bypass operation.
SUBJECTS AND METHODS. We performed a prospective study involving 355
patients undergoing routine chest CT examinations. To determine the prevalence
of anomalous right coronary artery imitation caused by this motion artifact,
all images were evaluated prospectively by an experienced radiologist.
RESULTS. Twenty-one patients (5.9%) were suspected of having a
malignant variant of the right coronary artery. However, in all patients prior
chest CT or additional coronary MR angiography showed a normal origin of the
right coronary artery.
CONCLUSION. Routine chest MDCT without retrospective ECG gating may
produce artifacts around the aorta simulating a malignant variant of the right
coronary artery. Considering the low incidence of this malignant interarterial
variant, the need for routine chest CT examinations combined with ECG gating
and further workup can be disputed from an economic point of view. This
artifact should be known to avoid unnecessary further examinations.
Introduction
Congenital coronary artery anomalies are rare and occur in 0.3-1.3% of the
population
[1-3].
Most morphologic variants of anomalous coronary arteries are not thought to be
hemodynamically significant; however, some anomalies are considered malignant
and carry the risk of sudden cardiac death. Particularly in children and young
adults, they are among the main causes of sudden cardiac death
[2,
4-7].
These include an ectopic coronary vessel originating from the pulmonary
artery, a single coronary artery, or a coronary artery originating from the
opposite aortic sinus and taking a course between the aortic root and the
right ventricular outflow tract
[2]. The interarterial course
of the right coronary artery (RCA) is the second most common coronary anomaly
and the most common malignant variant
[4]. It is considered malignant
because an impingement of the anomalous coronary artery by the aorta and
pulmonary trunk can occur, especially during exercise. Other theories explain
the malignant characteristic by the limitation of flow due to a sharp vessel
bend or an ostial stenosis at the aberrant origin.
The current diagnostic method of choice for detecting coronary artery
anomalies is MR angiography; conventional X-ray coronary angiography is often
difficult because it provides only a 2D view of the coronary artery tree
[8]. MDCT has also been shown
to be useful for noninvasive visualization of the coronary arteries
[9,
10]. However, routine chest CT
examinations for reasons other than suspected coronary diseases are usually
performed without retrospective ECG gating. Except for dedicated
postprocessing, effective slice thicknesses of up to 5 mm are routinely
reconstructed, leading to limited spatial resolution in the z-direction and
thus impaired depiction of the coronary artery tree. Although pulsation
artifacts in general are well known and have been described in the literature
[11], to our knowledge no
evaluation exists of aortic root artifacts simulating a malignant variant of
the RCA. Therefore, we prospectively investigated the incidence of patients
suspected of having a malignant interarterial course of the RCA on routine
untriggered chest MDCT.
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Fig. 1A —Axial MDCT scans through ascending aorta (AA) obtained with
16-MDCT scanner in 25-year-old man with testicular neoplasia. Note artifact in
front of aortic root simulating interarterial course of right coronary artery
(RCA) (arrow). Another motion artifact can be seen behind aortic
root. DA = descending aorta, LA = left atrium; PA = pulmonary artery.
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Fig. 1B —Axial MDCT scans through ascending aorta (AA) obtained with
16-MDCT scanner in 25-year-old man with testicular neoplasia. Prior CT image
shows normal RCA originating from right sinus of Valsalva
(arrow).
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Subjects and Methods
Study Group
CT examinations of 355 patients (212 men, 143 women; mean age. 49.4 years)
who underwent routine chest CT were included in this prospective study. The
proximal coronary arteries were evaluated concerning a possible malignant
interarterial course by an experienced radiologist. The diagnosis of possible
coronary anomaly was made on routine chest CT if no normal origin of the RCA
was visible and at the same time a linear structure was depicted between the
aortic root and the right ventricular outflow tract (Figs.
1A and
1B). The gold standard for
these patients was defined as depictable coronary arteries on prior chest CT
or normal coronary angiography. If neither chest CT nor coronary angiography
was available, MR imaging of the coronaries was performed to establish the
gold standard by noninvasive means.
The study protocol was approved by the institutional board of clinical
investigation, and informed consent was obtained from each subject
participating in this study.
MDCT
MDCT of the chest was performed on MDCT scanners (Somatom Volume Zoom
[n = 164] and Somatom Sensation 16 [n = 191], Siemens
Medical Solutions). Routine scanning parameters for examinations of the entire
thorax were a 4 x 2.5 mm collimation for the 4-MDCT scanner (120 kV; 100
mAseff; table feed per rotation, 15 mm; rotation time, 0.5 sec) and
a 16 x 1.5 mm collimation for the 16-MDCT scanner (120 kV; 100
mAseff; table feed per rotation, 30 mm; rotation time, 0.5 sec). In
all patients, IV contrast material was administered (Ultravist 370
[iopromide], Schering), followed by a saline chaser bolus using a double-power
injector. Derived from these MDCT data sets, axial slices were reconstructed
using soft-tissue kernels ("smooth," Siemens B30) and lung window
kernels ("sharp," Siemens B50) with an adapted field of view based
on the individual's physique, a standard matrix size of 512 x 512, and a
reasonable overlap (reconstruction increment, 4 mm).
MRI
MR angiography of the coronary arteries was performed on a 1.5-T Gyroscan
whole-body MR system (ACS-NT, Philips) using a 5-element cardiac Synergy coil
(2 anterior, 3 posterior elements) positioned at the level of the aortic root.
First, gradient-echo scout views were obtained in the coronal, sagittal, and
transverse planes. Then an ECG-triggered multiphase gradient-echo sequence
with echo-planar technique was performed to visually determine the optimal
rest period of the RCA during diastole. Thus the trigger delay for a
transverse free-breathing navigator-gated and cardiac-triggered 3D
steady-state free-precession sequence was determined (TR/TE, 4.3/2.0,
flip-angle, 75°, spatial resolution, 1.5 x 1.5 x 3
mm3) [12].
Results
In 21 (5.9%) of 355 patients, an anomalous RCA with an interarterial course
was suspected (Figs. 1A and
1B). Eight of these 21 patients
were examined on a 4-MDCT and 13 patients on a 16-MDCT scanner. In 11
patients, prior chest CT images showed a normal course of the RCA, and in one
patient a coronary angiogram was available for ruling out a malignant anomaly.
Nine patients without further studies underwent additional coronary MR
angiography (Figs. 2A and
2B).
In none of the 21 patients with a suspected malignant RCA variant on
routine chest MDCT was this diagnosis confirmed.
Discussion
Routine chest CT studies are usually performed without retrospective ECG
gating and consequently suffer from motion artifacts caused by transmitted
cardiac pulsation [13,
14]. Although this does not
hinder evaluation of the mediastinum and lungs, depiction of the coronary
arteries can be impaired, and diagnostic pitfalls such as intraaortic flaps
resembling dissection of the ascending aorta can occur
[14]. Figures
1A, and
1B shows a typical artifact
simulating an aberrant origin of the RCA from the left sinus, which to our
knowledge has not been described in the literature. Because of the
interarterial course between the aortic root and the pulmonary trunk, this
anomaly is considered a malignant variant, and coronary bypass surgery might
be considered to prevent sudden cardiac death. To assess the prevalence of the
previously described artifact on routine chest MDCT, we performed this
prospective study of 355 patients. The false-positive finding of possible
interarterial course of the RCA in 5.9% of our patient population is caused by
two factors. Transmitted cardiac motion artifacts cause the finding, which
simulates the aberrant RCA just in front of the aortic root (Figs.
1A and
1B, arrow). In addition, the
lack of depiction of a normal RCA—our second requirement for the
diagnosis of this coronary anomaly—is the result of the rapid movement
of the proximal RCA. Motion artifacts of the RCA are known to occur more often
compared with the left mainstem, left anterior descending, and left circumflex
coronary arteries because motion velocity of the RCA is substantially higher
[15]. Depending on the
relationship between the cardiac cycle and the acquisition phase of the CT
scan, objects up to 3 mm can vanish completely on the image
[16,
17]. Obviously, the time of
high-velocity movement of the RCA and pulsation of the aortic root accompanied
by the described artifact occur closely together during systole, leading to a
relatively common appearance of an artifact in front of the aortic root and a
lack of visualization of the normal RCA origin. Unfortunately, it was not
technically feasible to show the difference between ungated and ECG-gated CT
data.
The major flaw of our study, however, is the lack of any patients with a
true malignant coronary artery variant, which does not allow any statistical
calculations. Theoretically, specificity and likelihood ratio for a negative
test could be calculated, but because of the strong verification bias
[18]—gold standard
examinations were checked only for patients with a positive diagnosis—we
consider any statistical analysis inadequate. Because of the low prevalence of
true malignant coronary artery variants, the theoretic numbers needed to
include a substantial number of diseased patients are practically not
achievable. Nonetheless, one may draw the conclusion that misinterpretation of
an aberrant RCA with an interarterial course on untriggered routine chest MDCT
is so frequent that it is deemed unjustified to use triggered chest CT to make
this potentially consequential diagnosis. Even the application of
retrospective ECG gating to all chest examinations will not be a practicable
solution because the radiation exposure would increase significantly as a
result of thinner acquired slices and greater slice overlap. This in turn
would lead to prolonged examination times and consequently to respiratory
motion artifacts.
In conclusion, a detailed evaluation of the coronary artery anatomy without
ECG gating is still not technically feasible even with 4- and 16-MDCT
scanners. In case of clinical suspicion of a malignant coronary anomaly, MDCT
of the heart using retrospective ECG gating or coronary MR angiography should
be performed.
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Abstract
Introduction
