What causes the tulip bulb appearance of the aortic root on CT and MR?
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Answer:
The tulip bulb sign, or tulip bulb aorta, describes symmetric dilatation of all three sinuses of Valsalva with effacement of the sinotubular junction, tapering into an ascending aorta of normal or near-normal calibre. The bulbous root sitting on a narrower tube resembles a tulip bulb on its stem. It is the morphology of annuloaortic ectasia and is most often seen in Marfan syndrome, reported in a majority of affected adults, and in other heritable thoracic aortic disease such as Loeys-Dietz syndrome, vascular Ehlers-Danlos syndrome and bicuspid aortic valve aortopathy. It is best assessed on ECG-gated CT angiography or MR angiography, which allow reproducible sinus-of-Valsalva measurements. The pattern matters because it predicts progressive root dilatation, aortic regurgitation from annular stretching, and a substantially raised risk of type A dissection, and it drives the timing of prophylactic root replacement or valve-sparing repair.
Why is it called so?
The symmetrically dilated aortic root sitting above a normal-calibre ascending aorta resembles the rounded bulb of a tulip on its narrow stem.
Pathophysiology
In Marfan syndrome and related connective tissue disorders, abnormal fibrillin-1 and dysregulated TGF-beta signalling degrade the elastic lamellae of the aortic media. The aortic root, subjected to the highest pulsatile stress in the arterial tree, dilates first and most. Because the medial weakness is uniform around the circumference, all three sinuses expand together rather than asymmetrically, and the dilatation extends up to and effaces the sinotubular junction while the more distal ascending aorta, with different wall composition and lower wall stress, remains comparatively spared. Stretching of the aortic annulus pulls the cusps apart and produces central aortic regurgitation.
Alternative names: Tulip bulb aorta, annuloaortic ectasia
Other associated named signs: Cobweb sign and intimal flap of a complicating dissection, and the dural ectasia and protrusio acetabuli of Marfan syndrome
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