Thoracic Imaging 2003 - Society of Thoracic Radiology
Thoracic Imaging 2003 - Society of Thoracic Radiology
Thoracic Imaging 2003 - Society of Thoracic Radiology
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TUESDAY<br />
166<br />
<strong>Thoracic</strong> Vascular Abnormalities in Children<br />
Sandra Kramer, M.D.<br />
Department <strong>of</strong> <strong>Radiology</strong>,<br />
The Children's Hospital <strong>of</strong> Philadelphia and The University <strong>of</strong> Pennsylvania School <strong>of</strong> Medicine<br />
INTRODUCTION<br />
Pediatric vascular abnormalities range from inconsequential<br />
normal variants to life threatening lesions with pr<strong>of</strong>ound effects<br />
on the airway and pulmonary parenchyma. Some congenital<br />
thoracic lesions such as sequestration may be detected in utero<br />
on prenatal sonograms and fetal MRI. Infants with significant<br />
vascular abnormalities <strong>of</strong>ten present in the neonatal period with<br />
respiratory or cardiovascular symptoms. Some anomalies<br />
become evident later in childhood, and other congenital lesions<br />
are discovered incidentally in adults. Acquired vascular lesions<br />
in children may be iatrogenic or result from trauma or underlying<br />
genetic or systemic diseases. <strong>Imaging</strong> plays a key role in<br />
evaluating the thoracic vasculature and its pathology.<br />
CONGENITAL ANOMALIES<br />
Vascular Rings<br />
In the first 5 weeks <strong>of</strong> fetal life, six pairs <strong>of</strong> aortic arches<br />
form and then regress segmentally or entirely. The paired 4th<br />
aortic arches connect the ascending aorta (primitive ventral aortic<br />
sac) to the descending aorta (embryonic left dorsal aorta).<br />
Most <strong>of</strong> the embryonic right 4th aortic arch regresses, leaving<br />
the normal left aortic arch with a left-sided descending aorta.<br />
Vascular rings result from interruptions in development <strong>of</strong> these<br />
primitive arches. Severity <strong>of</strong> symptoms such as expiratory stridor,<br />
wheezing, and dyspnea depends on the degree <strong>of</strong> tracheal<br />
compression by the vascular structures.<br />
Careful evaluation <strong>of</strong> chest radiographs may reveal a "right<br />
aortic arch" on the AP view and anterior bowing and narrowing<br />
<strong>of</strong> the trachea on the lateral projection. Since it is impossible to<br />
determine the exact anatomy <strong>of</strong> the vascular ring using plain<br />
radiographs and barium swallow alone, MR imaging is used for<br />
this purpose. The two common vascular rings are:<br />
1. Double aortic arch. The most complete type <strong>of</strong> vascular ring<br />
occurs when both embryonic fourth aortic arches remain<br />
patent and surround and compress the esophagus and trachea.<br />
Multiplanar MR images show both components <strong>of</strong> the<br />
double arch and their compressive effects on the airway. The<br />
right arch is typically larger and more cephalad than the left.<br />
2. Right aortic arch with an aberrant left subclavian artery. The<br />
most common vascular ring, although in some cases it may<br />
be asymptomatic. The vascular ring surrounds the trachea<br />
and esophagus, closed by the ductus or ligamentum arteriosum,<br />
which is almost always left-sided. MR imaging shows<br />
the right arch, the course <strong>of</strong> the descending aorta and the<br />
segmental impression on the trachea by the aberrant left subclavian<br />
artery. An "aortic diverticulum <strong>of</strong> Kumerol", a focal<br />
enlargement at the origin <strong>of</strong> the aberrant left subclavian<br />
artery, may also be seen.<br />
Pulmonary Sling (Aberrant Origin <strong>of</strong> the Left Pulmonary<br />
Artery)<br />
The pulmonary "sling" is an unusual vascular anomaly in<br />
which the aberrant left pulmonary artery originates from the<br />
posterior aspect <strong>of</strong> the right pulmonary artery and passes<br />
between the trachea and esophagus to reach the left hilum.<br />
Underlying tracheobronchial abnormalities are associated with<br />
pulmonary sling including tracheomalacia and "complete" cartilaginous<br />
rings causing tracheal and bronchial stenosis. The lateral<br />
chest radiograph may show a small mass between the trachea<br />
and esophagus. Bilateral or unilateral hyperinflation may<br />
be present depending on the degree <strong>of</strong> tracheal or bronchial<br />
stenosis. On barium swallow an impression caused by the aberrant<br />
left pulmonary artery is visible on the posterior wall <strong>of</strong> the<br />
trachea and the anterior wall <strong>of</strong> the barium filled esophagus. CT<br />
and MRI demonstrate the complete anatomy <strong>of</strong> the pulmonary<br />
sling and the airway narrowing.<br />
Pulmonary Lesions with Anomalous Vasculature:<br />
Sequestration<br />
Bronchopulmonary sequestrations are foci <strong>of</strong> pulmonary tissue<br />
that lack normal communication with the tracheobronchial<br />
tree and have a systemic arterial blood supply. Most <strong>of</strong> these<br />
lesions are discovered incidentally on chest films. Further evaluation<br />
usually involves contrast enhanced CT. The contrast bolus<br />
is timed to show optimal enhancement <strong>of</strong> the feeding artery and<br />
lung parenchyma. On MRI, sequestrations are well-defined<br />
lesions with bright T2 signal intensity, with the feeding artery<br />
and draining veins identified. Sequestration may also be diagnosed<br />
in utero on prenatal ultrasound and MRI examinations.<br />
Two forms <strong>of</strong> sequestration have been described:<br />
1. Extralobar sequestrations are enclosed in their own pleural<br />
layer, with an arterial supply via small branches <strong>of</strong>f the aorta<br />
and venous drainage into the azygous or hemiazygous system.<br />
They are most commonly found in the posterior<br />
costophrenic sulcus, primarily on the left, and less commonly<br />
in the mediastinum and upper abdomen. More than half <strong>of</strong><br />
patients with extralobar sequestrations have other congenital<br />
anomalies.<br />
2. Intralobar sequestrations are enclosed within the pleura <strong>of</strong><br />
the adjacent normal lobe. Their arterial supply is variable,<br />
but usually from aortic branches that lie in the inferior pulmonary<br />
ligament, and drainage occurs into the pulmonary<br />
veins. These lesions may be found in older children with no<br />
other congenital anomalies.<br />
Hypogenetic Lung Syndrome<br />
In scimitar syndrome one lung is hypoplastic and is drained<br />
by an anomalous pulmonary vein. Its feeding artery is usually a<br />
hypoplastic pulmonary artery, but may be <strong>of</strong> systemic origin.<br />
There may be abnormal bronchial branching or bronchial<br />
hypoplasia. Pulmonary segmentation anomalies may coexist.<br />
This anomaly is found predominantly on the right and is associated<br />
with congenital heart disease in approximately 25% <strong>of</strong><br />
patients, most commonly atrial septal defect. Since the scimitar<br />
vessel usually drains into the junction <strong>of</strong> the inferior vena cava<br />
with the right atrium, a left-to-right shunt occurs. When scimitar<br />
syndrome presents in infancy, it is usually in the setting <strong>of</strong> congestive<br />
failure. These lesions are, however, <strong>of</strong>ten asymptomatic,<br />
found incidentally on chest radiographs. The typical radiographic<br />
feature is the anomalous pulmonary venous trunk coursing