Effect of Aortic Arch Position on the Bronchial Length Ratio in Situs Determination.

BACKGROUND: Bronchial length ratio (BLR) is widely used for situs determination. However, BLR may also be influenced by the position of the aortic arch. We aimed to evaluate the effect of aortic arch position on BLR. METHODS: Patients were identified using the keywords left aortic arch (LAA), right aortic arch (RAA), double aortic arch, situs inversus, right isomerism, and left isomerism. The ratio between the longer and shorter bronchi was calculated. BLR and bronchopulmonary arterial relationship were compared across groups with different combinations of body situs and aortic arch position. RESULTS: Patients included 69 with situs solitus and LAA (group 1A), 20 with situs inversus and RAA (group 1B), 43 with situs solitus and RAA (group 2A), 2 with situs inversus and LAA (group 2B), 11 with situs solitus and double aortic arch (group 3), and 14 with right or left isomerism (group 4). Group 2 demonstrated a significantly smaller BLR than group 1 (P = 0.001). Group 3 showed a smaller BLR than group 1 but without statistical significance. Group 4 had a significantly smaller BLR than groups 1-3 (P < 0.001). None of group 1 had a BLR within the heterotaxy range. BLR ranges of 11% of group 2 and 9% of group 3 overlapped with the heterotaxy range. Bronchopulmonary arterial relationship was consistent with the situs of the remainder of the body in all. CONCLUSIONS: BLR is influenced by aortic arch position, limiting its use for situs determination. Bronchopulmonary arterial relationship should be used as the primary criterion for situs determination.