Effect of various thoracic radiographic projections on the appearance of selected thoracic viscera

To assess the effect of different radiographic projections on thoracic width, as well as position and visibility of the trachea, principal bronchi, cardiac silhouette, aorta, caudal vena cava (CVC) and oesophagus.

Right lateral recumbency (RLR), left lateral recumbency (LLR), dorsoventral (DV) and ventrodorsal (VD) thoracic radiographs of 42 dogs were reviewed retrospectively.

In 78 per cent of cases the thoracic width was significantly larger on the VD projection than on the DV projection. The angle of divergence formed by the principal bronchi was significantly larger on the VD projection than on the DV projection in 80 per cent of dogs. A cardiac silhouette bulge at 1 to 2 o'clock was apparent on the VD projection in 22 per cent of dogs but was never seen on DV projections. The descending aorta was more visible at the 4 to 5 o'clock cardiac silhouette level on the DV projection and laterally at the T8 level on LLR projections. The CVC was better seen on VD and LLR projections. The oesophagus was visible as a soft tissue opacity in LLR in large dogs with normal thoracic conformation in 35 per cent of cases.

The DV projection appears to be more reliable for assessing the cardiac silhouette, the descending aorta and the angle of divergence of the principal bronchi. The VD projection should be considered for evaluating the CVC. LLR should be used for assessing the descending aorta and CVC.