Case 93
Patent ductus arteriosus: MRI findings
Clinical findings
A 29-years old man had an auscultatory finding of
continuous murmur.
The patient underwent MRI examination and aortography
(TR= 85 % RR; TE= 24; slice thickness= 3 mm; gap= 0)
(FA= 30°;TR= 40; TE= 12; slice thickness= 3mm)
Imaging findings
shows the interruption of the internal border of the distal aortic
arch (arrows).
shows a tubular hyperintense image (arrows) linking the distal aortic arch to
the left pulmonary artery.
Diagnosis
Patent ductus arteriosus
Discussion
Patent ductus arteriosus (PDA) is one of the most frequent
congenital anomaly in children (10 %) but is uncommon in grown ups. If the
ductus does not close spontaneously within two months of birth, it will usually
be patent into adulthood.
The severity of symptoms in grown ups depends on
the size of the PDA, the presence of pulmonary hypertension and the direction of
the shunt.
Congestive heart failure is a common cause of death in adults
affected by PDA.
The condition consists in a communication between the
proximal left pulmonary artery and the inferior aspect of the distal aortic
arch, beyond the ostium of the left subclavian artery.
The PDA, found in
grown ups, is similar to the small ventricular septal defect, with either normal
or near-normal pulmonary artery pressure and a small left to right
shunt.
Two-dimensional Doppler echocardiography provides high-quality images
of the aortic arch in children, because of the easy availability of the
suprasternal notch and high right parasternal windows.
Furthermore the small
size of infants and children allows the use of high-frequency transducers, such
as 5 MHz and 7.5 MHz ones, which provide high resolution images and the
detection of small structures.
Opposite, these transducers are impractical in
grown ups because of the inadequate penetration. Moreover a complete evaluation
of the aortic arch may be difficult in grown ups because of the limitation of
available windows, presence of ribs, chest deformities and body habitus (2,
6).
MR imaging is noninvasive, does not need the injection of contrast
material and is less exspensive than aortography. It is able to image the entire
aorta in multiple planes (1, 3-5).
MR imaging has a huge field of view and a
high contrast resolution. Furthermore it does not have the limitations of
echocardiography in grown ups, such as chest deformities, body habitus and
presence of avalaible windows. Therefore MR imaging is more suitable than
echocardiography in the evaluation of adults (2,6).
The patient, we studied,
was a young adult, aged 29 years. MR imaging showed a small patent ductus with a
length of 4 mm and a caliber of 2.5 mm, linking the distal aortic arch to the
left pulmonary artery. No sign of pulmonary hypertension was observed since the
pulmonary arteries were normal.
The visualization of the patent ductus
required the use of 3 mm thick sagittal slices with no interslice gap, which is
rather challeging for a .5 T MR imager.
Signal to noise ratio was improved by
increasing the number of excitations to five and subsequently the acquisition
time.
Patent ductus arteriosus was first detected with cardiac-gated SE
imaging. Cine-MR GE helped confirming SE imaging finding and allowed an
angiographic-like visualization of the anomaly.
Aortography confirmed the MR
imaging diagnosis.
Our experience demonstrates MR imaging is a reliable
method in the detection and assessment of even small patent ductus arteriosi in
grown ups.
References
1) Gomes AS: MR imaging of congenital anomalies of the
thoracic aorta and pulmonary arteries. Radiol Clin North Am 27: 1171-1181, 1989.
2) Gutierrez FR, Canter CE, Mirowitz SA: MR evaluation of the congenital
heart disease patient : techniques, strategies and interpretative approach. In :
Gutierrez FR, Brown JJ, Mirowitz SA (eds) Cardiovascular magnetic resonance
imaging. Moby Year Book, New York, 1992.
3) Higgins CB, Byrd BF, Farmer DW et al : Magnetic resonance imaging in
patients with congenital heart disease. Circulation 70 : 851-860, 1984.
4) Higgins CB : Congenital heart disease. In : Higgins CB, Hricak H, Helms CA
(eds) MRI of the body. Raven Press, New York, 1992.
5) Higgins CB, Silvermann NH, Kersting-Summerhof BA et al: Congenital Heart
Disease. Raven Press, New York, 1994.
6) Wexler l, Higgins CB : The use of magnetic resonance imaging in adult
congenital heart disease.Am J Cardiac Imaging 9 : 15-28,1995.