Biomed Imaging Interv J 2006; 2(2):e11
doi: 10.2349/biij.2.2.e11
© 2006 Biomedical Imaging and
Intervention Journal
CASE REPORT
Spiral CT angiography in an infant with a hypoplastic
aortic arch
S Man Harun,
MBBS, MRad, Y Faridah,
MBBS, MRad
Department of Biomedical Imaging (Radiology), Faculty of
Medicine, University of Malaya, Kuala Lumpur, Malaysia
ABSTRACT
The advent of multislice computed tomography (CT) has revolutionised the performance
of body CT and allowed the development of CT angiography (CTA).
CTA is a robust and minimally invasive method of visualizing
the arterial vascular system. The newer generation of multidetector
scans has allowed for shorter scanning times with no respiratory
misregistration at peak vascular opacification following peripheral
contrast injection. The volume of data obtained from these scans
can be further manipulated to generate two-dimensional (2D)
and three-dimensional (3D) images with no increase in radiation
to the patient. Hence, CTA has gained popularity and importance
as the alternative diagnostic tool especially for ill patients
in which conventional angiography is inadvisable.
We present an infant with coarctation of the aorta and hypoplastic
aortic arch, in which CT angiography was used to pinpoint the diagnosis. The CT
findings were subsequently confirmed at surgery. © 2006 Biomedical Imaging and
Intervention Journal. All rights reserved.
CASE REPORT
A full term newborn was noted to have poor Apgar score at
birth. Physical examination revealed differential cyanosis with maximal upper
limb and lower limb saturation difference of more than 10%. The child also had
a heart murmur with absent femoral pulses bilaterally. On day two of life, the
child developed respiratory distress and was admitted to the intensive care
unit for ventilation.
Chest x-ray demonstrated cardiomegaly with congested lung
fields. Echocardiogram suggested the presence of a hypoplastic transverse arch.
She also had a moderate sized muscular ventricular septal defect with
bi-directional shunting. As the patient was ill, CT angiography with 3D
reconstruction was performed rather than a conventional angiography.
Spiral CT imaging was carried out using GE Lightspeed
16-slice multidetector CT (GE Healthcare, Milwaukee, Wisconsin, USA). A bolus
application of 5 mL non-ionic contrast (l.5 mL/kg body weight) followed by 5 mL
of bolus saline was hand-injected via a peripheral venous cannula. Scanning
commenced after 50% of contrast volume was injected. Spiral CT of the aortic
arch and aorta was performed, starting at the level of the thoracic inlet
vessels down to the mid abdomen in 1.25 mm slice thickness. KV was set at 120
while mA was set at 220. Total scan time was 12 seconds, during which the
ventilation was withheld. Axial slices were reconstructed with a 60% overlap
(0.75 mm / l.25 mm). Subsequently, 2D and 3D reconstructions from various
angles were produced with standard software.
Spiral CT showed that the arch was hypoplastic (Figure 1).
The left subclavian and the left internal thoracic arteries arise from the
descending aorta distal to the hypoplastic arch. The left common carotid artery
arises from the left subclavian artery. Immediately distal to the origin of the
left subclavian artery, there is a stenosis of the descending thoracic aorta in
keeping with post-ductal coarctation (Figure 2). The intercostals arteries are
well seen arising from the descending thoracic aorta distal to the coarctation.
There is cardiac failure as the hepatic veins are dilated and the lungs appear
congested. The pulmonary artery is large and patent, and the pulmonary veins
drain normally into the left atrium.
On day 14 of life the child underwent open-heart surgery and
the CT findings were confirmed. It was noted that the degree of hypoplasia of
the transverse arch was severe and would have caused difficulty in cardiac catheterisation,
a traditional method of diagnosing this condition.
DISCUSSION
Coarctation of the aorta with concomitant hypoplastic aortic
arch is a rare congenital anomaly affecting the cardiovascular system [2].
Traditionally, diagnosis is made at cardiac catheterisation [3]. Cardiac catheterisation
is an invasive procedure and therefore is fraught with complications especially
when performed in ill infants. Furthermore, the severity of the hypoplastic
arch could cause difficulty in cardiac catheterisation as was noted intraoperatively
in this patient.
An exciting alternative such as CT angiography with 3D
reconstruction may provide similar if not superior findings as conventional
angiography. There is an added advantage in that the surrounding structures are
also delineated on CT scan. The spectrum of indications for CT examination has
expanded since the introduction of the spiral CT technique, especially with
regards to vascular abnormalities. This is mainly attributed to faster scanners
and the ability to perform 2D and 3D reconstructions without additional
radiation to the patient. High quality 2D reconstructed images are generated
from transaxial scans provided that image data was acquired with a thin
collimation and transaxial images were generated with a high degree of overlap [4].
In addition, Maximum Intensity Projection (MIP) reconstructions can be rendered
in any projection, including projections impossible to obtain with conventional
angiography [5]. MIP is a volume-rendering technique in which parallel rays
pass through the volume of data and the maximum CT number encountered in each
ray is displayed [1]. Therefore MIP permits separation of the enhanced lumen
from the surrounding structures.
In comparison with angiography, where several injections of
contrast media are necessary, CT angiography can be performed following single
bolus injection of contrast media and in this case only a total of 5 mL was
used. The disadvantages of CTA such as side effects of contrast media could be
disregarded in comparison to cardiac catheterisation, which uses a higher
volume of contrast.
The main limiting factor of CT examination would be the
radiation dose. In this patient, the estimated effective dose of the patient is
in the region of 10.6 mSv for CT imaging of chest to the mid abdomen [6]. A
conventional diagnostic cardiac angiography would generally produce median
effective dose of about 4.6 mSv for a paediatric patient [7]. However the
effective dose during cardiac catheterisation increases in newborn with
effective doses ranging from 6.5 mSv at 50th percentile to as high as 18.0 mSv
at 90th percentile [8]. Therefore, the radiation dose of CTA in newborns is
comparable to that of conventional cardiac catheterisation. In this case, the
CTA gave invaluable information regarding the patient’s diagnosis and
subsequent treatment. Furthermore, the grave condition of the patient
necessitates the non-invasive approach of CT.
Other techniques such as ultrasound and MRI have its
advantages in cardiac imaging. However, 2D echocardiography is operator
dependent and as this is a rare case, an exact diagnosis was difficult to
achieve. MRI was not performed due to the long examination time and the need
for arrested respiration to achieve images of diagnostic quality, which is unsuitable
due to the unstable condition of the patient.
Thus, CT angiography has become a promising procedure for
the visualisation of vascular disorders. It has a shorter examination time, and
a reduced number of projections and amount of contrast media are needed
compared to cardiac catheterisation. Its radiation dose is comparable to that
of conventional angiography in the newborn. In addition, CTA is helpful for
pre-operative planning as the localisation, shape and length of the stenosis,
as well as the course of the collateral vessels, can be assessed clearly.
CONCLUSION
In conclusion, spiral CT angiography is proven to be a
reliable method in demonstrating anomalies of the aorta in a paediatric
patient. It is also a practical clinical test that may be an alternative to
cardiac catheterisation, especially in delineating extracardiac vascular
structures.
APPENDIX
Two movie clips showing 3D reconstructed CT angiography of the procedure performed for this case report is available for download at: http://www.biij.org/2006/2/e11
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Received 24 May 2005; received in revised form 24 January 2006; accepted 7 February 2006
Correspondence: Department of Biomedical Imaging, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia. Tel.: +603-79502069; Fax: +603-79581973; E-mail: yangf@um.edu.my (Yang Faridah A. Aziz).
Please cite as: S Man Harun, Y Faridah, Spiral CT angiography in an infant with a hypoplastic aortic arch, Biomed Imaging Interv J 2006;2(2):e11
<URL: http://www.biij.org/2006/2/e11/>
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