Membranous Septal Aneurysm: An Unusual Cause for Right Ventricular Outflow Tract Obstruction in a Malaligned Ventricular Septal Defect with Aortomitral Discontinuity (Double-Outlet Right Ventricle) Associated with Visceral Heterotaxy

The development of a septal aneurysm in the natural history of membranous ventricular septal defects usually makes the defect hemodynamically less significant. This report describes a case of severe right ventricular outflow obstruction produced by a membranous septal aneurysm in a patient who had an anterior malaligned ventricular septal defect with aortomitral discontinuity (double-outlet right ventricle). This patient did not have pulmonary stenosis other than the dynamic obstruction produced by the septal aneurysm. In this patient, the septal aneurysm produced both favorable and unfavorable hemodynamic effects. A reduction in the size of the ventricular septal defect produced a favorable effect, whereas a right ventricular outflow obstruction led to the unfavorable situation of right ventricular hypertension and hypertrophy. The large septal aneurysm in the presence of an already compromised right ventricular outflow tract related to an anteriorly malaligned septum resulted in severe obstruction.