An aneurysm is a weakness and thinning of a blood vessel wall. Blood flowing past this weak area can push against this spot and form a bulge. Sometimes the lining of the blood vessel wall tears and blood goes down between the two layers. This is called a dissecting aneurysm.
A false aneurysm (also called pseudoaneurysm) is a leakage of blood from an artery into the nearby tissue. There's an actual hole through all layers of the artery. Blood spurts out of the hole and collects in a cavity that's walled off.
The leak can result from an artery being punctured during a test such as a cardiac catheterization or an arteriogram. It can also occur during surgery of the spine. The large blood vessel called the aorta is very close to the spine. The artery can be easily damaged during an operation.
Some pseudoaneurysms heal without treatment. Others need to be repaired to prevent too much blood loss.