Accessory valve cusp as a cause of outflow tract obstruction in atrio-ventricular and ventriculo-arterial discordance.

Congenital corrected transposition of the great arteries in which there is both an atrio-ventricular and a ventriculo-arterial discordance has surgical significance only in consequence of the associated cardiac anomalies. Their surgical correction is subject to multifarious problems. An exceedingly rare cause of a left-ventricular outflow tract obstruction erroneously interpreted preoperatively in an eight-year-old boy is reported. In an l-transposition with inversion of both ventricles, the diagnosis "valvular pulmonary stenosis" was made preoperatively. However, a normally arranged tricuspid pulmonary valve without stenosis was revealed intraoperatively. On the other hand, dystopic valvular tissue in the form of a monocuspid atrioventricular valve which was attached to an accessory papillary muscle with several tiny tendons was found below the pulmonary valve in the morphological left ventricle. The accessory valve cusp, which was the cause of the hemodynamically relevant subvalvular pulmonary stenosis, had no connection with the mitral valve. The abnormal valve cusp was resected without injuring the normal structures. The angiographic follow-up after one year no longer revealed any pressure gradient. This case report points out the possibility of an outflow tract obstruction caused by a complete accesory valve cusp.