Stenosis of the mitral valve causes resistance to the flow of blood from the LA to LV. The LA dilates. Blood will then accumulate in the lungs causing pulmonary congestion. The pulmonary vessel will then respond to long standing congestion by arteriolar vasoconstriction. This will cause rise in pulmonary artery pressure (pulmonary hypertension) and will partly relieve pulmonary congestion. Pulmonary hypertension may – if severe – cause severe right ventricular, hypertrophy, dilatation and failure, and right atrial dilatation and may end in congestive heart failure
X-ray Picture
Mild stenosis of the mitral valve causes dilatation of the left atrial appendage and straightening and mitralization of the left border of the heart.
As the stenosis becomes more severe pulmonary congestion will start to appear and left atrial dilatation will progress until the right border of the left atrium extends beyond the right border of the heart. However, extreme left atrial enlargement is rarely seen except if there is associated mitral regurgitation. Severe cases will show Kerley A lines in the lungs which are straight, dense lines up to 4 cm in length running toward the hilum. Kerley’s B lines are also seen as dense short horizontal lines most commonly present in the costophrenic angles and are caused by edema and thickening of interlobular septa
The pulmonary hypertension will then set in causing severe dilatation of the main pulmonary artery and its branches. The left border of the heart will show small aortic knob due to reduced cardiac output followed by a convexity representing the enlarged pulmonary artery then another convexity due to the dilatation of left atrial appendage followed by the cardiac apex which may be displaced outwards by right ventricular enlargement
Mild mitral stenosis
Moderately severe mitral stenosis causing left atrial enlargement
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