In stulas with a small ori ce, less than 3 mm, locally applied treatments can be tried and can be relatively safe and easy.

Endoscopic Techniques

Stents

There are two types of stents that we can consider to use for the treatment of ADF: silicone stents and self-expanding metallic stents (SEMS).

Silicone stents were rst invented and placed by J.F. Dumon for the treatment of benign and malignant tracheobronchial stenosis as well as ADF. They are available in different con gurations: straight and Y-shaped stents, with studs on the outer surface designed to avoid migration. In the case of the treatment of long aero-digestive

stulas, Dumon prostheses have the drawback that they can prevent complete closure of the s- tula if the studs further injure in the stulous tract; for this reason SEMS prostheses increasingly replaced Dumon prostheses in the airway for the treatment of ADF.

First generation of metallic stents, Gianturco stainless steel wire stents or Strecker stents, made of tantalum were early abandoned due to poor fexibility and adaptability, and high complication rate.

The so-called second generation of SEMS include the Wallstent—self-expandable with internal silicone-based covering with fared ends, made of a stainless steel alloy woven into a tubular mesh—and the Schneider prosthesis—a cobalt-based superalloy—both inserted using a fexible beroptic bronchoscope.

Subsequently, these prostheses were improved giving place to self-expanding metal stents, cov-

ered with silicone (third generation) to avoid the important problems of the non-covered self-­ expanding metal prostheses (such as granulomatous or tumor growth through the metal mesh, generating obstructions and re-epithelialization of the mucosa involving the metallic wires that make extraction almost impossible).

Examples of third-generation airway stents are: Ultrafex Stent, made of nitinol (nickel–tita- nium alloy) uncovered or covered by silicone, Aero Stent made of nitinol and covered by polyurethane, and Micro-Tech Stent and Aerostent made of nitinol and completely covered by silicone. Also, the Bona Stent (made of nitinol and covered by silicone) and the NiTi Stent (made of nitinol and covered by polytetrafuoroethylene) are currently the most frequently chosen last-­ generation stents.

Nitinol alloys give the stent two important characteristics: pseudoelasticity effect, that is, an elastic response to an applied stress, and shape-­ memory effect, that is, maintaining a deformed shape at body temperature. These two effects are due to the thermodynamic and crystallographic structure of the elements conforming the stent.

Easy deployment and the ability to achieve better apposition to the airway mucosa are the two most important qualities of SEMS. These stents can be inserted and deployed with a ber-

optic bronchoscope and they are very adaptable to changes in both the direction and caliber of the airway. The advantage of these stents is that they adapt much better to the tracheal wall deformities, but also have the inconvenience of generating infammatory and granulomatous tissue growing in the mucosa. The lifespan of these stents is short, so metal fatigue and stent fracture can occur.

As we mentioned before, both silicone and self-expanding metal covered stents have been used for treatment or ADF (Figs. 39.4, 39.5, 39.6, and 39.7).

The rst approach to seal ADF should be esophageal stent [38]. Placement of the esophageal prosthesis is not dif cult, except when thestulae are located near the ends of the esophagus or there is an esophageal stenosis. In those cases, the procedure could be more complicated or sometimes impossible.

Self-expanding stents are more widely accepted for use in the esophagus since it manages to seal the stulous ori ce more ef ciently. However, there are two important drawbacks for those stents: one is due to their self-expanding property—if the size is not carefully selected, an oversized stent can stretch the lumen with its expansible radial forces, and can increase the s- tula due to excessive expansion of the esophageal

wall. There is also the additional risk of penetration through the airway wall. SEMS can also migrate more frequently than silicone stents since they have a smooth outer surface (36 Eliminar).

When silicone stents are chosen, we have to take into account that the studs (covering the external wall of Dumon stents) can prevent a good sealing and more than that, they can further