Imaging diagnosis
Case 119
【Progress】He got diuretics, which helped his symptoms of general fatigue improved, indicating that his aortic bicuspid valve still was functioning well.
He is scheduled to check annual health care examination of stomach and heart.
【Discussion】
It is necessary to refresh structure and mechanism of valves in heart before studying bicuspid aortic valve. There are five valves in heart; aortic valve, pulmonary valve, tricuspid valve, mitral valve and inferior vena cava valve. Inferior vena cava valve plays an important role before birth to preserve an oxygen-containing blood flow route from placenta, umbilical vein, hepatic vein, inferior vena cava, right atrium, oval foramen, and left atrium. There exists no valve in superior vena cava because its venous return is following the direction of gravity. Valve itself is formed to prevent the backflow of blood flow.
Aortic valve, pulmonary valve and tricuspid valve compose of three leaflets, called tricuspid valve, while mitral valve and venous valve compose of two leaflets, called bicuspid valve. Each leaflet is supported by attachment to fibrous tissue (chordae tendineae) connected to papillary muscle that contract to prevent prolapse of valves into atrium during ventricular systole. When valve opens, opening space is larger in tricuspid valve than bicuspid valve, indicating that tricuspid valve is more appropriate for much volume outflow of blood than bicuspid valve. When valve closes, closure surface is less in bicuspid valve than tricuspid valve, indicating bicuspid valve closure is tighter and more tolerant than tricuspid valve.
Therefore, mitral valve is preferred to be bicuspid valve to endure and to prevent back flow of blood under high pressure by left ventricle systole. Left atrium appendage functions as a decompression chamber during left ventricular systole and during other situation such as mitral valve disease when left atrial pressure is high (1). Meanwhile, other three valves including aortic valve is preferred to be tricuspid valve for allowing much volume of blood outflow to whole body.
Bicuspid aortic valve (BAV) occurs in 1-2% of the population and with male predominance (3 : 1) (2-4). BAV associates with aortic coarctation in approximately 25 % (2-4). BAV is the most common cause of aortic valve stenosis and regurgitation under 65-year-age group, and post-stenotic dilatation of ascending aorta whose size of 5 cm or greater which is a potential intervention candidate (2-4). BAV has two leaflets which are asymmetric and the larger leaflet results from leaflet fusion. The fusion line sometimes deposit calcification. CT is superior to MRI to detect BAV in showing leaflet-fusion calcification. Enhanced CT using contrast medium shows a specific finding of an elliptical shaped “fish mouth” in a diastole phase. Our patient was a male aged 63 (2-4) and enhanced CT showed these typical findings of BAV (Fig. 1).
【Summary】
We present a sixty three-year-old male suffering from general fatigue, high value of brain natriuretic peptide and pleural effusion. His parent had cardiac valve diseases. Enhanced CT using contrast medium showed an elliptical “fish mouth” configuration with calcification corresponded to the leaflet fusion. We should keep in mind that aortic valve, pulmonary valve and tricuspid valve have three leaflets valve, while mitral valve and inferior vein valve have two leaflets valve. Mitral valve and left atrium appendage might be created to endure high pressure by left ventricle systole. Bicuspid aortic valve which whose large leaflet results from the fusion of leaflets, is the most common cause of aortic valve stenosis and post-stenotic dilatation of ascending aorta. Bicuspid aortic valve (BAV) occurs in 1-2% of the population and with male predominance (3 : 1). The typical findings of CT are calcification on the fusion of the leaflets and a “fish mouth” configuration during a left ventricle diastole.
【References】
1.Al-Saady NM Left atrial appendage: structure, function, and role in thromboembolism Heart. 1999;82:547-554.
2.Verma, S, et al. Aortic dilatation in patients with bicuspid aortic valve. New England Journal of Medicine (Review). 2014: 370 (20): 1920–1929.
3.Mahadevia R, et al. Bicuspid aortic cusp fusion morphology alters aortic three-dimensional outflow patterns, wall shear stress, and expression of aortopathy. Circulation. 2014; 129 : 673–682.
4.Bissell MM, et al. "Aortic dilation in bicuspid aortic valve disease: flow pattern is a major contributor and differs with valve fusion type". Circulation: Cardiovascular Imaging. 2013; 6 : 499–507.
2018.9.5