Anomalous papillary muscle causing tethering of the mitral valve.

Herein is described a rare case of anomalous papillary muscle (APM) insertion which caused severe mitral regurgitation (MR). In this case, the anterolateral papillary muscle inserted directly into the left ventricular surface of the anterior mitral leaflet (AML), without an intervening chorda. The APM pulled the AML down towards the left ventricle, causing a marked tethering of the mitral valve. The dilatation and dysfunction of the left ventricle exacerbated the tethering of the mitral valve, which eventually caused severe MR. At surgery, after resection of the APM, the mitral valve was replaced with a prosthetic valve. A directly inserting APM, which is known as a rare cause of a left ventricular outflow tract obstruction, seems to transmit a stronger tethering force to the mitral leaflet than does a normal stay chorda. Thus, the present case shows that this type of APM might cause MR due to a mechanism of valve tethering.