[A successful surgical case report of subaortic stenosis due to accessory mitral valve tissue associated with partial ventricular septal hypertrophy].

One-year- and ten-month-old male infant with subaortic stenosis due to the accessory mitral valve tissue associated with asymmetrical myocardial hypertrophy was treated successfully with surgery. Preoperative diagnosis of "discrete subaortic stenosis" was achieved by echocardiography and angiography. A 70 mmHg of preoperative pressure gradient from left ventricle through ascending aorta could be reduced to 25 mmHg by the operative excision of this accessory mitral valve tissue and partial resection of this septal hypertrophy. This patient was supposed to be complicated with the ventricular septal aneurysm according to the angiographic study, even though this aneurysm was not visualized at the time of the operation. According to our knowledge, only fifteen cases of stenosis due to accessory mitral valve tissue was reported. The pathological findings of the excised specimens of these anomalous tissue were presented and developmental genesis of this intracardiac anomalous tissues, perhaps based on the developmental anomaly of the primitive organ of the endocardial cushion, was discussed in this report.