Arterial dissection
Arterial dissection occurs when there defect in the arterial tunica intima, leading to blood entering a virtual space between the tunica intima and tunica media. This forms a so-called false lumen inside this space. The false lumen may become larger than the true lumen. Blood may flow out of the false lumen through a second intimal tear.
The aorta is the artery most often affected by dissection, called aortic dissection.