Chiari anomalies in the human right atrium ostensibly are encountered rarely. There is only sporadic mention in the literature of these fenestrated, net-like valves of the inferior vena cava, coronary sinus, or various strands connecting these with other right atrial structures. The effects of such structural anomalies on heart function are unknown. We report here gross observations of the right atrial net from among 213 cadavers, 38 autopsied, and 11 fetal hearts. Histological and ultrastructural examination of inferior vena cava and coronary sinus valves demonstrated that only the anomalous coronary sinus valves contained cardiac muscle. Chiari anomalies typically have referred to perforations or tissue strands related to the inferior vena cava valve and possibly the coronary sinus valve. The anomaly commonly is cited as occurring in 2% of individuals, although there has been no study to support this. We observed Chiari malformations in 13.6% of the 213 cadaver hearts, and 10.5% of the autopsied hearts examined. Of these malformations, the coronary sinus valve was fenestrated most frequently. We propose the term "right atrial net" for "Chiari net," for anomalies involving valves of the inferior vena cava and coronary sinus, and strands within the right atrium connecting these valves with the crista terminalis, right atrial wall, or interatrial septum.

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