Computed tomographic angiography chest results at initial admission. Innominate artery demonstrates distinct widening on coronal oblique view (a) after takeoff from the aortic arch. This (red arrow, a) represents the origin of dissection, which separates the true lumen (below red arrow, a) from the false lumen (above red arrow, a). Extension distally into the subclavian artery is observed (pink arrow, a). Axial imaging (b) shows true and false lumens in both the subclavian artery (red arrow, b) and the axillary artery (pink arrow, b), evidencing distal extension of dissection. Aortic involvement is absent—no true and false lumens are identified.