Partial obliteration or blurring of the descending aortic contours: a pitfall on plain chest radiographs

We report the cause and clinical significance of partial obliteration or blurring of the descending aortic contour on the frontal chest radiographs of patients without pathology in the vicinity of the descending aorta. Among 112 cases, 26 cases (23.2%) showed obliteration or blurring of the contour (positive group). On the corresponding computed tomograph of the positive group, two dominant causes were shown. One was contact between the descending aorta and the left hilar or lower lobe vessels. The second was the adjacent pleura being obliquely orientated to the anteroposterior (A-P) axis. In the latter group, on the lateral chest radiographs, a flattened thorax with a smaller A-P diameter was seen. Identification of left hilar or lower lobe vessels on a frontal chest radiograph or a diminished A-P diameter of the thorax on a lateral radiograph is useful in differentiating these circumstances from true thoracic pathology.