Sub-mitral membranous curtain: A potential anatomical basis for congenital Sub-mitral aneurysms

To seek an anatomic basis for congenital sub-mitral aneurysms. 75 normal human autopsy heatts were incised between the right and left coronary cusps up to the apex. The membranous septum was trans illuminated from the right side. The mitral valve was lifted anteriorly to observe extension of any membranous tissue to the sub-mitral region. In 17 out of 75 hearts, the tissue of the membranous septum extended beyond the nadir of the non-coronary cusp, beneath the aortic leaflet of the mitral valve, up to the postero-medial commissural line. In 28 hearts, this sub-mitral membranous extension continued beyond the postero-medial commissural line beneath the annulus of the mural leaflet, to a distance varying from 4mm to 21mm, with height between 0.5mm to 4mm. This extension of the membranous tissue beyond the nadir of the non coronary cusp, caudal to the aortic and mural leaflets of the mitral valve is preferably labeled sub-mitral curtain. The sub-mitral curtain was in continuity with the membranous, septum in 40 hearts. In 5 hearts, trans illumination was interrupted between membranous septum and sub-mitral curtain by varying extent of opaque area due to tissue of the central fibrous body, right fibrous trigone and ventricular musculature. The membranous sub-mitral curtain of the mitral valve seen in 45 out of 75 hearts is a potentially weak area, through which congenital sub-mitral true aneurysms can occur.