Thoracic Imaging 2003 - Society of Thoracic Radiology

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