Identification of thoracic isomerism from the plain chest radiograph.

Abstract

Plain chest radiographs of 14 patIents with congenital cardlac malformations associated wIth situs ambiguus were retrospectively reviewed to establish diagnostic radiographic signs from both frontal and lateral projections. Cardiac diagnosis was previously established by angiocardlography in each of the 14 patIents and by supplemental anatomic Inspection in 10. RIght thoraclc Isomerism was present in six patients and left thoracic Isomerism in eight. Analysis of frontal projections showed similar length of right and left bronchus (mean ratio, 1 .13 ± 0.09) In each patient, and similar anatomic relations between each bronchus and Its respective pulmonary artery (i.e., eparterIal or hyparterlal), previously shown to be useful radiographic signs of situs amblguus. The diagnosIs of situs amblguus could also be suspected from the lateral projection of the plain chest film, a finding not previously reported. This projection usually shows the right and left bronchus posterIor to the respective pulmonary artery In patients with right Isomerism (usually associated with asplenia) and each bronchus Inferior and anterior to the correspondlng pulmonary artery in those with left isomerism (usually associated with polysplenla). Radiographic crIterIa were listed for diagnosis of sItus amblguus and for separation into left and right Isomerism from each projection to compare their usefulness. Frontal and lateral films from 14 patIents In the study group (situs ambiguus) were compared with the 29 patIents in a control group (three with situs inversus and 26 with situs solitus). These 86 films were randomized and reviewed “blindly” by three radiologists In 258 observatIons. Eleven errors in diagnosis (4.3%) were made by the observers: one film of a patient with situs inversus was diagnosed as situs solitus and 10 films of patients with situs ambiguus were incorrectly reported as situs solitus. A total of 84 observations was made of 14 patients with situs ambiguus with two false negatives and no false positIves. A total of 48 observations of eight patients with left isomerism was made with seven errors. A total of 36 observations of patients with right Isomerism was made with four errors . There was no significant difference between the false positive and false negative error rate using frontal or lateral views (P < 0.50). These data permit the conclusion that the frontal and lateral views of the plain chest film are independently equally useful in allowing the suspicion of the diagnosis of situs ambiguus and in separating left from right Isomerism.