Complete atrioventricular canal associated with conotruncal malformations: anatomical observations in 13 specimens

Conotruncal anomalies associated with atrioventricular (AV) canal defects are more common than is generally appreciated on clinical grounds. Among 39 specimens of AV canal malformations, 13 (33%) presented with conotruncal abnormalities: a complete form of AV canal has been observed in all. 5 cases exhibited visceral situs solitus, 5 situs ambiguus with asplenia and 3 situs ambiguus with polysplenia. In the first group, conotruncal anomalies were tetralogy of Fallot in 3 cases, bilateral conus with double outlet right ventricle (DORV) in 2, one with subpulmonary ventricular septal defect (VSD) and the other with doubly commited VSD. Survival in these patients was relatively longer (average 20 mth) and the clinical course was mainly determined by the degree of the pulmonary outflow obstruction: surgical correction should have been feasible in these cases. Patients with situs ambiguus, both with asplenia and polysplenia, had further severe cardiovascular malformations associated with AV canal which led to early death (average survival 12 days): anomalous pulmonary and systemic venous return and univentricular hearts. In the latter patients, tetralogy of Fallot, bilateral conus with DORV and pulmonary atresia were the conotruncal malformation. Retrospectively, in no case of the last category a complete repair had been accomplished. All but one specimen presented the complete form of AV canal with 'free floating anterior leaflet' and hypoplastic anterior tricuspid component. This hypoplasia could be interpreted as missing conal tissue in the development of the anterior tricuspid cusp. For this leaflet a dual embryological origin, both from the dextro-dorsal conal ridge and the right lateral AV cushion, is suggested.