mitral valve stenosis
mitral valve obstruction can either be due to a supravalvar ring close to the valve orifice obstructing mitral flow, or to papillary muscle abnormality. a parachute mitral valve is where the papillary muscles are fused or one is severely hypoplastic. mitral valve anomalies are uncommon in children. mitral stenosis may occur as an isolated lesion but is much more common in association with other left heart obstructive disease such as coarctation, aortic or subaortic stenosis. in the latter situation, sometimes known as shone’s syndrome, mitral stenosis is often not revealed until after the obstruction in the arch and left ventricular outflow tract (lvot) are relieved. if mitral stenosis is severe in early life, the neonate will present with congestive cardiac failure or failure to thrive. removal of a supravalvar ring or mobilization of the papillary muscles may be attempted. this is not always successful and mitral valve replacement may be necessary. valve replacement is problematic in children as an artificial valve has to be replaced with growth and anticoagulants are necessary.
the four chamber view in the fetus will be abnormal if the degree of stenosis is more than mild due to enlargement of the left atrium. it may be markedly dilated if the atrial septum is restrictive. there will be a left to right shunt at atrial level. there will be decreased and turbulent flow across the mitral valve on colour flow mapping with the valve excursion limited to a variable degree. a single papillary muscle may be detectable, instead of the normal two, in the short axis view of the left ventricle. the left ventricle will usually be decreased in size. if mitral stenosis occurs as part of a shone’s complex, the hypoplastic aortic arch, coarctation, aortic valve dysplasia and small left ventricle may be the dominant findings.
the dilated left atrium can be mistaken for a cystic structure in the posterior thorax. blood flow within the chamber on colour flow mapping should identify this as the left atrium. the small size of the left ventricle may be misdiagnosed as a hypoplastic left heart but this diagnosis should be reserved for cases of mitral and aortic atresia, that is where both valves are completely obstructed.
- systemic lupus
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