Hamartomatous malformation in the mitral valve's anterior leaflet

We report a previously undescribed (to our knowledge) anomaly of the mitral valve's anterior leaflet: a cystic lesion that protruded from the atrial surface in the midportion near the base. The lesion consisted of large, irregularly shaped, endothelial-lined spaces separated by trabeculae of tissue containing atrial myocardial fibers. The endothelial-lined spaces communicated with the left ventricular cavity through an opening on the ventricular surface of the leaflet. Inasmuch as the anterior mitral leaflet arises embryologically by fusion of the endocardial cushions, the location of the lesion suggests that an anomaly in the fusion process might have been involved.