A stenosis (from Ancient Greek στενÏŒς, "narrow") is an abnormal narrowing in a blood vessel or other tubular organ or structure. It is also sometimes called a stricture (as in urethral stricture). Stricture as a term is usually used when narrowing is caused by contraction of smooth muscle (e.g. achalasia, prinzmetal angina); stenosis is usually used when narrowing is caused by lesion that reduces the space of lumen (e.g. atherosclerosis).[citation needed] The term coarctation is another synonym, but is commonly used only in the context of aortic coarctation. Spinal stenosis is a narrowing of the spaces within your spine, which can put pressure on the nerves that travel through the spine. Spinal stenosis occurs most often in the lower back and the neck. Some people with spinal stenosis may not have symptoms. Others may experience pain, tingling, numbness and muscle weakness. Symptoms can worsen over time. Spinal stenosis is most commonly caused by wear-and-tear changes in the spine related to osteoarthritis. In severe cases of spinal stenosis, doctors may recommend surgery to create additional space for the spinal cord or nerves. Many people have evidence of spinal stenosis on an MRI or CT scan but may not have symptoms. When they do occur, they often start gradually and worsen over time. Symptoms vary depending on the location of the stenosis and which nerves are affected.