Aneurysms of the main pulmonary artery are rare. About half are attributed to congenital heart disease and are usually associated with pulmonary hypertension. Acquired causes include infection (syphilis, tuberculosis, bacterial endocarditis), vasculitis (Behcet's and Hughes-Stovin syndromes), connective tissue abnormalities (Ehlers Danlos, Marfan's, cystic medial necrosis), and trauma (including malpositioned Swan-Ganz catheters causing iatrogenic pulmonary artery pseudoaneurysm). The aforementioned causes need to be excluded before idiopathic dilatation of the pulmonary artery is considered.
CECT parameters for a normal pulmonary artery are:
1. transverse diameter of main pulmonary artery < 28-29 mm, measured at the bifurcation, perpendicular to the long axis of the artery,
2. main pulmonary artery with a smaller diameter than the adjacent aorta,
3. transverse diameter of right interlobar artery < 16 mm.
Focal dilatation of the pulmonary artery exceeds these parameters. In addition to a dilated main pulmonary artery, CECT may also show enlargement of the right and left pulmonary arteries.
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