Mitral valve annulus (anatomy)

The mitral valve annulus is part of the fibrous skeleton of the heart. It consists of a ring of collagenous tissue that surrounds and supports the left atrioventricular orifice. It forms the attachment of the mitral valve leaflets by fusion with their intermediate layer, the lamina fibrosa.

The annulus is not uniformly thick throughout its circumference:

• to the right, it is attached to the right and left fibrous trigones of the fibrous skeleton
• between the trigones, the space is bridged by an extension of the lamina fibrosa of the anterior valve leaflet inferiorly to merge with the fibrous subaortic curtain
• long subendocardial fibrous thickenings pass from each trigone around the annulus - the fila coronaria; with distance laterally, they taper in thickness
• the space between the ends of the fila coronaria is bridged by a thin layer of fibrous tissue

The structure of the annulus contributes to the dynamics of mitral valve opening.