Thoracic situs as an indicator of atrial appendage morphology: a postmortem study of 306 specimens with situs solitus in 250 and heterotaxy in 56 cases.

Symmetry of bronchi, lung lobation, and atrial appendages is frequently found in patients with heterotaxy syndromes. To evaluate the reliability of thoracic situs as an indicator of atrial appendage morphology, thoracic situs was assessed in 306 postmortem cases: 250 with atrial situs solitus and 56 with heterotaxy syndromes. Five features that indicate thoracic situs were assessed: (1) lung lobation, (2) lengths of main bronchi, (3) ratio of left to right (L/R) bronchial lengths, (4) relationship of bronchi to ipsilateral pulmonary artery, and (5) number of cartilage rings in each main bronchus. In the group with heterotaxy, the expected symmetrical lung lobation, lengths of bronchi, number of cartilage rings, and relations to pulmonary arteries were found in 77, 77, 77, and 95% of cases, respectively. The ratios of L/R bronchial lengths were ≤ 1.5 in 90% of cases. The relations of the bronchi to the pulmonary arteries were the best predictors of symmetrical atrial appendages or splenic syndromes. Bronchial-atrial discordance occurred in ten cases: in situs solitus in one case and in heterotaxy in nine cases. Detection of heterotaxy syndromes is important because of the associated severe congenital cardiac defects. No single feature of thoracic situs is completely reliable. All available data should be used to make the diagnosis.