Thoracic Imaging 2003 - Society of Thoracic Radiology

vertically along the right atrium toward the right cardiophrenic
angle with the appearance of a "scimitar". CT shows the course
of the "scimitar" vein through the hypoplastic right lung to the
inferior vena cava as well as the pulmonary artery and airway
anomalies.
HEREDITARY HEMORRHAGIC TELANGECTASIA
Rendu-Osler-Weber (ROW) is an autosomal dominant vascular
disorder. It remains unclear whether the vascular lesions are
true congenital malformations or acquired lesions occurring in
abnormal vessels. Pulmonary arteriovenous malformations
(PAVM) occur in about 20% of patients with ROW and include
vascular abnormalities ranging from telangiectatic lesions to
large arteriovenous channels. Most PAVM are found during adolescence
and young adulthood, although symptoms may occur
in childhood and infancy. Complications include hemorrhage
into the bronchi or pleural cavity, hypoxemia due to right-to-left
shunting, and embolization across the vascular lesion into the
systemic circulation, especially to the CNS. PAVM may be seen
on a chest radiograph depending on their size and location,
however, they are better assessed by CT and pulmonary angiography.
The size, number, location and architecture of the lesions
can be defined prior to angiographic embolization.
MARFAN SYNDROME
Marfan syndrome is an autosomal dominant disorder of connective
tissue with variable penetrance. The most serious cardiovascular
complications include aortic root dilatation, aortic dissection
and aortic valve insufficiency. MR imaging can define
these complications involving the ascending aorta and aortic
valve. Aneurysms of the pulmonary vasculature, dilatation of
the abdominal aorta, and aneurysms at the origin of peripheral
aortic branch vessels are also encountered in Marfan syndrome.
MR imaging is also valuable in the post-operative evaluation of
complications following composite graft placement and in
screening of family members of Marfan patients.
VASCULITIS
Vasculitis involving the pulmonary arteries is rare in children,
but occurs in Wegener's granulomatosis and Churg-Strauss
vasculitis. It may accompany systemic connective tissue diseases
such as systemic lupus erythematosus and dermatomyositis.
Although imaging findings are helpful, lung biopsy is
required for the definitive diagnosis.
Wegener's granulomatosis
Wegener's granulomatosis, a necrotizing vasculitis with granuloma
formation, involves the respiratory tract and kidneys.
Although nodules and cavities occur frequently in adults, these
features are found less often in children. The most common
radiographic findings in children include diffuse interstitial and
alveolar opacities. High-resolution CT scans may portray a pattern
of perivascular, centrilobular hazy opacities, which correlate
with biopsy findings of perivascular inflammation and surrounding
hemorrhage.
Takayasu arteritis
Takayasu arteritis is a chronic inflammatory arteritis of
unknown etiology that results in thrombosis, stenosis, dilatation
and aneurysm formation in the aorta, aortic branch vessels and
pulmonary arteries. Concentric mural calcification and mural
thickening in the aorta and pulmonary arteries may occur. Early
symptoms may have an insidious onset and include dyspnea and
hemoptysis. The disease may progress to vascular dissection,
cerebrovascular accident and heart failure resulting from aortic
insufficiency.
MR and contrast enhanced CT are helpful in the initial diagnosis,
follow-up of progression, and assessment of response to
treatment. CT shows the thickened vascular wall, contour
changes of stenosis or dilatation and mural calcification. MR
imaging may depict the size and extent of contour abnormalities,
as well as the thickened wall and mural thrombi, but mural
calcification may not be visible. Cine gradient echo MR
sequences may show pulmonary and aortic valvular insufficiency.
Contrast enhanced MR images have been reported to demonstrate
increased signal in the thickened vascular walls and surrounding
periaortic tissues due to intramural neovascularity in
cases with acute and chronic active arteritis.
OTHER ACQUIRED VASCULAR ABNORMALITIES
Thoracic aneurysms
Thoracic aortic and pulmonary artery aneurysms are very
rare in infants and children, but may be seen in patients with
connective tissue disease, such as Marfan and Ehlers-Danlos
syndromes. They are more frequently the sequela of surgery or
prior vascular intervention such as umbilical arterial catheterization
in the neonatal period. In these settings, a mycotic
aneurysm may go unrecognized clinically during the course of
treatment for fever of unknown origin or endocarditis.
Depending on the location of the lesion, it may or may not be
visible on chest radiograph and echocardiography. CT or MRI
may demonstrate an unsuspected mycotic aneurysm and provide
the details of location and extent of the aneurysm necessary for
surgical management. In addition cine gradient echo sequences
may show turbulent flow into an aneurysm as well as valvular
insufficiency in the case of valvular-based aneurysms.
Traumatic aortic injuries
Traumatic aortic injuries are uncommon in children and are
most often the result of motor vehicle accidents. The aortic isthmus
is the most commonly injured site and most of these
patients have additional severe injuries. Common radiographic
findings in aortic injury include mediastinal widening, apical
capping, poorly defined aortic contour, and displacement of the
course of the NG tube. Enhanced spiral CT is a valuable screening
tool for aortic injury in stable patients. Typical CT features
of aortic injury include intimal flap and pseudoaneurysm formation,
as well as mediastinal hematoma, pleural fluid and pulmonary
parenchymal injury. Angiography also has an important
diagnostic role.
CONCLUSION:
Pediatric thoracic vascular abnormalities range from benign
anatomic variants discovered incidentally to potentially lifethreatening
lesions. Many lesions come to clinical attention
because of their effects on the airway, pulmonary parenchyma
or cardiovascular system. Diagnostic imaging frequently begins
with plain film radiography and may progress to cross-sectional
imaging with CT and MRI. These imaging modalities have
largely replaced more invasive techniques such as angiography
and provide valuable data contributing to patient management.
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