Double-outlet right ventricle without ventricular septal defect. A challenge to the embryologist? microscopic investigation

Summary

A male infant died at the age of four weeks with the following clinical diagnosis: ventricular septal defect, patent ductus arteriosus, total heart block. Postmortem X-ray investigation of the heart-lung-specimen (in which the aorta and the pulmonary trunk had a normal interrelationship, with an approximately normal caliber) and succeeding dissection of the heart chambers, revealed that both great arteries took their origin from the right ventricle; there was no ventricular septal defect and consequently the non-functioning left ventricle was rudimentary; ductus arteriosus and foramen ovale were patent.

The lack of a ventricular septal defect, from embryologic viewpoint an almost obligatory part of the well-known entity of double-outlet right ventricle, compelled an extensive microscopic serial investigation of the central part of the heart septum (with the adjacent parts of tricuspid and mitral valves) and the outflow tract of the right ventricle, including the arterial orifices and a paraseptal flap of the ventral right ventricular wall.

In the ventricular septum, underneath the lower left aortic semilunar cusp, at the usual site of the pars membranacea, a large mass of chondroïd tissue was found, coherent with a vast area filled with inflammatory cells, calcification, necrosis and another, smaller-sized piece of chondroid tissue in the left ventricular septal wall. Furthermore, there was pronounced endocardial fibro-elastosis of the left ventricle, demarcated by a ring of numerous thick-walled arteries with narrowed or even occluded lumina, and with several conspicuous communicating channels toward the left ventricular cavity (arterio-luminal vessels).

Most likely this malformation was the result of an embryonic inflammatory process, started before the 16 mm stage and involving the region of the foramen interventriculare so violently as to occlude it before the aorta had reached its left ventricle.

The endocardial fibro-elastosis, the large arterio-ventricular communications and the coronary arterial lesions are attributed to the exceeding pressure in the blind left ventricular cavity and the associated ischemia in the left ventricular wall. The ischemia might also have contributed to the aberrant cartilage formation.

The significance of the findings for the functional, embryological and anatomical distinction from the usual type of double-outlet ventricle is emphasized.