The procedure was successful, according to a statement form Cheney's office
Cheney suffered from popliteal aneurysms (pronounced POP-li-teel AN-yur-isms). That means that the artery running behind each knee had developed a bulge.
Abdominal aortic aneurysms are more common -- and, because they tend to rupture, far more deadly. But popliteal aneurysms usually don't rupture. Instead, they tend to throw off blood clots. When that happens, the leg may have to be amputated.
When a popliteal aneurysm is found, surgery is the best option, says vascular surgeon Peter Henke, medical director of the Noninvasive Diagnostic Vascular Laboratory at the University of Michigan. Without treatment, patients who already have symptoms run a one in five risk of losing a leg and a one in 20 chance of dying.
"Patients generally should have it fixed, because the risk of complication does not correlate with the size of a popliteal aneurysm," Henke tells WebMD. "A small one is just as dangerous as a big one."
How the Surgery Is Done
Fixing a popliteal aneurysm is relatively simple. It means taking a blood vessel from the lower leg and using it to bypass the bulge in the artery. The graft usually runs from above the knee to below the knee.
"Overall this works quite well," Henke says. "Overall, 80% to 90% of the grafts are still fine after five years."
However, it's not a good sign to have a popliteal aneurysm. Some 70% of people who have these aneurysms also have abdominal aortic aneurysms, Henke says. Fixing an abdominal aortic aneurysm is a much more involved surgery, although less invasive techniques can be used for some patients.
That technique -- endovascular repair, which avoids open surgery -- is also showing surprisingly good results for popliteal aneurysms in early trials.
Possibly because of his heart condition, Cheney underwent this less invasive surgery. Instead of a bypass graft, doctors use a catheter to insert a mesh tube -- called a stent -- through the bulging part of the artery. This strengthens the artery.
The procedure is far less intense than bypass surgery, according to the Society for Vascular Surgery. It's performed under local anesthesia.
Doctors generally recommend bypass operations, as the flexing of the knee puts a lot of wear and tear on stents. But Henke says that in clinical trials, the stents are working better than many surgeons had expected.
Fortunately, popliteal aneurysms are relatively rare. Only 0.1% of the U.S. population gets them -- and for reasons not yet understood, nearly all of them occur in men. Some 5% of men over 55 get popliteal aneurysms.
The main risk for popliteal aneurysms is smoking.