D-Bulboventricular Loop with L-Transposition in Situs Inversus

Abstract

In the case described anatomically corrected transposition of the great vessels is associated with situs inversus. Anatomically corrected transposition is extremely rare, and has not been previously reported with situs inversus. This type of transposition should not be confused with classical corrected transposition. Thus the case examined exhibited a D-bulboventricular loop with L-transposition and atrial inversion, so that blood flow was physiologically incorrect as in classical complete transposition. In the case examined, it was also found that bulbar musculature was present between the aorta and the mitral valve. Additional study of the conducting tissue revealed inversion of the sinoatrial node with the atria, and also of the atrial portion of the atrioventricular node. The atrioventricular bundle and its branches were in expected positions in relation to a large ventricular septal defect. These results are discussed with regard to previous reports and to the embryology of the conducting tissue.