Supravalvular mitral ring with mitral stenosis

Supravalvar mitral ring is a circumferential ridge or membrane arising from the left atrial wall overlying the mitral valve and frequently attached to the mitral valve.1 Variable in thickness and extent, the ring ranges from a thin membrane to a thick discrete fibrous ridge.2 The membranous variety may be difficult to detect because the membrane often adheres to the anterior mitral valve leaflet while remaining just proximal to the posterior mitral leaflet. Adhesion to the valve may impair the opening of the leaflets, and this impairment may be the main mechanism of mitral valve inflow obstruction in some patients. In other patients, the ring may be large enough to protrude into the mitral valve inflow and cause obstruction. The supramitral ring may initially be incomplete and eccentric, allowing for an unobstructed flow through the mitral valve. However, turbulence can cause a progressive increase in the supravalvar membrane or ridge thickness, worsening mitral inflow obstruction.3 The same mechanism is responsible for the acquired variety of supravalvar mitral stenosis, which occurs after mitral annuloplasty for the repair of mitral regurgitation.