Metal Stents

Gianturco stents are constructed from metal stainless steel monofilament wires, fashioned in a zigzag pattern with 5 to 10 bands.4 The lengths of the stents are 2.5 cm for tracheal stents and 2 cm for bronchial stents. These stents can be delivered through a 12F introducer sheath. These stents are also available as tandem stents with double the length of the single stents. Because of problems with migration, small hooks are placed along the proximal and distal ends to allow for anchoring into the airway wall.

The Wallstent airway prostheses are made from woven stainless steel monofilament wires, fashioned to form a cylindrical mesh. These stents are longitudinally stretched to compress into an introducer sheath and, as such, shorten upon the self-expansion of deployment (Figure 40-1C). Because of the larger contact area than the Gianturco stent, Wallstents do not require hooks to prevent migration. The Wallstent has excellent flexibility and conformance to the airway anatomy. Problems with ingrowth of tumor or granulations through stent interstices have been largely alleviated by coating the Wallstent with a thin layer of sil-icone rubber (Permalume). There is still 5 mm of bare metal stent at each end to help stabilize the stent and prevent migration, but these areas may still result in tissue ingrowth and secondary stent obstruction.

The Ultraflex stent is made from a single strand of nickel-titanium alloy (nitinol) woven into a cylindical mesh. The increased heat of the body produces self-expansion of the thermal-triggered shape

Lung Stents Rubber

memory property of the stent, once released from its delivery catheter. Both covered and uncovered versions are available, and because of the single-strand nature of the construction, endoscopic retrieval is more feasible than with a Wallstent or Gianturco stent.

The Palmaz stent is a fixed diameter stent made of stainless steel, with staggered rows of rectangular slots around the entire circumference. These stents require balloon expansion to deploy them in the airway and expand the stent to its functional diameter. Once expanded, the Palmaz stent does not exert a continual expanding pressure on the airway. There is no covered version of the Palmaz stent, and after tissue ingrowth occurs, removal is very difficult.

The Strecker stent consists of a single tantalum filament interwoven into a cylindrical wire mesh. These stents are very flexible and do not shorten longitudinally when dilated, making placement easier, particularly in short segment stenoses. Like the Palmaz stent, Strecker stents require balloon expansion during deployment to produce the desired stent diameter and they do not produce the intrinsic radial force of self-expandable stents.

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