Dissecting flap is seen involving the descending thoracic aorta starting distal to the left subclavian artery and extending downward to the common iliac arteries. The true lumen is anterior while the false lumen is posterior and larger. Both are patent yet the false lumen shows a crescent shape irregular thrombus at distal thoracic segment. Both renal arteries are patent, the left renal artery arise from the true lumen while the right renal artery arises from both false and true lumina. The celiac, superior and inferior mesenteric are patent and arise from true lumen.