Recognition and management of accessory mitral tissue causing severe subaortic stenosis.

Failure to recognize the presence of accessory mitral tissue causing subaortic stenosis can lead to not only the performance of inappropriate operations, but the persistence and recurrence of obstruction or even death. Over a 12-month period, we treated 2 children with severe subaortic stenosis caused by accessory mitral tissue. In 1 patient, who was 4 years old, the echocardiogram showed the accessory mitral tissue to be attached to the anterior mitral leaflet and ballooning into the subaortic area. The other patient, as a newborn, underwent simultaneous repair of a complete canal defect and coarctation. Two years later, the patient was seen because of syncopal episodes, progressive mitral insufficiency, and subaortic stenosis thought to be caused by anterior displacement of the anterior mitral leaflet. Mitral valvuloplasty and a conal enlargement procedure were planned. Intraoperatively, after the mitral valvuloplasty had been done, the subaortic stenosis was found to be due to a tight subaortic ring formed by accessory mitral tissue located at the septum and its fibrous extension to the anterior mitral leaflet. In both patients, excision of the accessory mitral and fibrous tissues resulted in a wide-open subaortic area. Both patients had an uneventful hospital course, and follow-up echocardiography showed no noteworthy residual left ventricular outflow gradient. We believe that increased awareness and sophisticated echocardiographic techniques should lead to an increased recognition of accessory mitral tissue causing subaortic stenosis. Simple resection of the accessory mitral tissue and its secondary fibrous tissues can be curative.