Clinical:The normal area of the mitral valve is 4 to 6 cm2. Severe stenosis is associated with areas less than 0.8 cm2, and most valves are replaced when their area becomes less than 1.1 cm2. Mitral stenosis results in increased resistance to emptying of the left atrium. This produces a reduced left ventricular output and an increase in pulmonary venous pressure (a valveless system, thus LA pressures are transmitted directly to the vessels). Eventually this increased pressure is back transmitted to the pulmonary arteries. The pulmonary arteries undergo medial hypertrophy and intimal sclerosis in response, and pulmonary arterial hypertension results. Ultimately, the right ventricle hypertrophies, dilates, and then fails. Clinically there is a diastolic murmur and resting tachycardia as the heart attempts to supply more blood systemically. Rarely, patients with mitral stenosis can present with diffuse alveolar hemorrhage . Another rare, late sequella of mitral stenosis is parenchymal ossification . In approximately 0.6% of cases of mitral stenosis, a coexisting ASD may relieve the left atrial hypertension and promote the formation of a left to right shunt. This combination of findings is known as Lutembacher syndrome .
The two major factors influencing prognosis in mitral stenosis are the presence of pulmonary hypertension (triples operative mortality) and the presence of symptoms . Once more than mild symptoms develop, the prognosis for medical treatment decreases .
Etiologies of mitral stenosis include rheumatic heart disease (most commonly), congenital mitral stenosis, or an obstructing lesion such as a left atrial myxoma.
CXR: The left atrial appendage is the only portion of the left atrium that forms part of the left border of the heart. On PA radiographs it occupies the portion of the left heart border between the main pulmonary artery segment and the superior portion of the left ventricular contour. When left atrial pressure and volume are normal, this segment of the left heart border is concave. Early or mild enlargement of the left atrium may be detected as enlargement of the left atrial appendage with straightening of this segment of the left heart border. With continued enlargement, this segment will become convex. Another finding of left atrial enlargement include a "double density" in the mid-portion of the cardiac silhouette on the frontal view. A line from the mid-point of the right border of the double density to the midpoint of the border of the left mainstem bronchus should measure less than 7.5 cm (7.0 cm in females). A normal left atrium should also lie anterior to a line drawn down the center of the trachea on the lateral, non-rotated view. Other findings which can suggest LA enlargement include posterior esophageal displacement on barium swallow, elevation of the left mainstem bronchus, and straightening of the left heart border due to enlargement of the left atrial appendage. In cases of long-standing stenosis, the LA wall may calcify. Mitral valve calcification is only seen 10% of cases (Note: Calcification of the mitral valve annulus does not indicate mitral stenosis). Pulmonary venous congestion can be seen as the stenosis progresses. Since the left ventricle is unaffected by mitral stenosis it will remain normal . Later there is pulmonary arterial hypertension and right ventricular enlargement.
MRI: On MRI other findings of mitral stenosis include a mild increased signal intensity in the lungs on spin echo images due to pulmonary venous hypertension and interstitial edema. Cine gradient images can be used to demonstrate turbulent flow across the mitral valve which appears as a fan-shaped signal void in the LV below the valve during diastole.
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