[Chest radiographic diagnosis of dissecting thoracic descending aorta]

Widening of the aortic shadow on chest radiography is one of the first indicators of aortic dissection. The degree of widening of the aortic shadow was estimated on two successive chest radiographs (mean [+/-SD] interval 0.8 +/- 0.7 years) before and after aortic dissection in 11 patients (four with DeBakey classification type I, seven with type III dissection). The distance between the center of each thoracic vertebra and the lateral margin of the descending aortic shadow (L) was measured. Since only a supine frontal film is usually available in acute aortic dissection, chest radiographs in both erect and supine positions were compared in 18 patients with hypertension. On supine films, L was larger than that on erect films, but the difference (delta L) was minimal (+2.6 mm) at the level of the tracheal bifurcation. Therefore, the L at the level of tracheal bifurcation (Lb) was best suited for comparing films taken in different positions. On supine films, Lb was significantly longer in patients with aortic dissection than in patients with hypertension (60.5 +/- 8.2 vs 46.0 +/- 7.9 mm, p < 0.001), and none with dissection showed Lb < 50 mm. Serial change of L over the follow-up of 1.4 +/- 0.7 years in patients with hypertension was also examined in erect films and was less than +1 mm. When the index film in a supine position was compared with the previous films in an erect position, delta Lb in patients with aortic dissection was +12.7 +/- 5.6 mm, which was significantly greater than that in patients with hypertension (+2.9 +/- 2.8 mm, p < 0.001). All 11 patients with aortic dissection showed delta Lb > or = +7 mm, but only one patient with hypertension (6%) exhibited this finding. Chest radiography is useful for identifying patients with aortic dissection, who characteristically show Lb > or = 50 mm on presentation and delta Lb > or = +7 mm, compared with previous films.