The radiological evaluation of atrial situs.

Visceral situs, as evidenced by the position of the stomach and liver on the plain film, does not predict atrial situs as accurately as does bronchial situs. In particular situs ambiguus of the atria is not reliably indicated by visceral situs, and its subdivision into either right and left isomerism, where both atria show either right or left morphology respectively, cannot be made. As a result serious abnormalities of venous connections, which are common in the isomerisms, can be missed. Bronchial situs indicates atrial situs much more reliably and can be determined from penetrated chest radiographs or tomograms since the right and left main bronchi normally show different lengths. A ratio of lengths of 2 : 1 or more diagnoses bronchial situs solitus if the longer bronchus is on the left or situs inversus if the longer bronchus is on the right. A ratio of 1.5 : 1 or less indicates an isomerism. Data are presented from which the type of isomerism can be deduced and ratios between 2 and 1.5 : 1 clarified as isomerism or no isomerism.