Aortic dissection

Aortic dissection is a tear inside the aorta, the body's main artery. It's uncommon, but when it happens, it's catastrophic. To understand it, you need to know that the wall of the aorta isn't one smooth, uniform sheet: it's made of layers. The innermost one is called the intima, and the middle one is called the media. In a dissection, the intima tears and the layers of the wall pull apart.

Blood moves through the aorta under pulsatile pressure, meaning it comes in surges, one with every heartbeat. When that pressure stays high for a long time, it gradually wears down the layers. If the intima tears, blood pushes into the crack, between the intima and the media, and opens up a false lumen. In medicine, the lumen is the hollow space that blood flows through; the false lumen is a second blood-filled channel that forms inside the wall itself. Picture a garden hose made of several layers bonded together: if the inner layer rips, the pressurized water no longer runs only down the middle. It slips through the tear and starts peeling the layers apart. That new channel expands and can take blood flow away from vital organs.

The classic way it shows up is sudden, intense pain in the chest or back, described as tearing. But it doesn't always come on that way: when the symptoms are subtler, the dissection is often missed.