A sudden infant death associated with atrial septal aneurysm and abnormality of the connecting site between the inferior vena cava and right atrium.

An atrial septal aneurysm (ASA) is a rare cardiac anomaly characterized by varicose bulgingofthe atrial septum (oval fossa) into the left or right atrium. Pathogenesis and clinical significance of ASA are controversial. We report an autopsy case of a huge undiagnosed ASA with abnormality of the connecting site between the inferior vena cava and the right atrial ostium in a 2-month-oldJapanesefemale who died suddenly and unexpectedly. She was born at 36 weeks 4 days (body weight 3,110 g). No abnormality was detected during pregnancy or delivery. The postnatal growth was normal with no cardiac problem detected at the 1-month checkup. The ASA bulged off in a mass to the left atrium (width, 0.8 cm; excursion ratio, 53%), reaching close to the inflow site of the right pulmonary vein, with dilation of the pulmonary vein. The connecting site between the inferior vena cava and the right atrium was atypically located 1.6 cm away from the atrioventricular groove. Although most cases of ASA in an infant resolve physiologically as the infant grows, the infant in the present case is thought to have had an exceptional pathological ASA, possibly causing supraventricular arrhythmia. The abnormality of the connecting site between the inferior vena cava and the right atrium might have affected the development and continuation of the ASA.