Stents are used on diverse structures such as the esophagus, trachea, or blood vessels. Prior to use, a stent is collapsed to a small diameter; when brought into place it is expanded using an inflatable balloon and is then held in place by its own tension. Stents are usually inserted by endoscopy or other procedures less invasive than a surgical operation, which makes them suitable for patients with advanced disease for whom an operation might be too dangerous. Stents may consist of wire mesh alone, or be covered by a tissue lining.