Isomerism of the atrial appendages: morphology and terminology

Our aim is to identify the pathognomonic anatomical markers and the best terminology to describe the cardiac malformations associated with absent or multiple spleens, which are known as asplenia or polysplenia syndromes or isomerism.

We have reviewed 65 hearts with isomerism of atrial appendages of the Anatomical Collections of Congenital Heart Disease, Institute of Pathological Anatomy of the University of Padua consisting of 1800 specimens. All the hearts were classified according to sequential segmental classification.

The incidence of isomerism was 3.6%. Of the total, 45 hearts with isomerism of right atrial appendages showed bilateral trilobed lungs, short bronchi, and absent spleen. The atrioventricular junction was univentricular in 49% of cases with a common atrioventricular valve in 91%. Pulmonary atresia and double outlet right ventricle were present in 40% and 47% of cases, respectively. Total anomalous pulmonary venous drainage and absent coronary sinus were always present. In 20 hearts with isomerism of left atrial appendages, bilateral bilobed lungs with long bilateral bronchi and multiple spleens were always found. The biventricular atrioventricular connection was present in 65% with a common valve in 30% of the hearts. The ventriculoarterial connection was concordant in 45% of cases, and aortic atresia and pulmonary atresia were both noted in 15% of each. An anomalous symmetric pulmonary venous drainage was observed in 65% of the hearts and interruption of inferior vena cava was found in 75% of cases.

We believe that the appropriate terminology is based on the symmetrical morphology of the atrial appendages. The absence of the coronary sinus and the total anomalous pulmonary venous drainage are the markers of isomerism of the right atrial appendages. Symmetric pulmonary venous drainage and interruption of inferior vena cava are the markers of isomerism of left atrial appendages. In recent years, thanks to the improvement of clinical diagnosis and of surgical techniques these patients have the possibility to survive to adult age.