Laryngeal and Tracheal Stents Workup

See the list below:

• The criterion standard for evaluating the larynx or the trachea is direct laryngoscopy and bronchoscopy.

• Fluoroscopy can be used to help define a narrowing of the trachea or abnormal radiographic appearance of the larynx. The diagnostic information yielded from fluoroscopy is inferior to that of direct laryngoscopy and bronchoscopy in the operating room (OR); however, radiopaque stents can be placed under fluoroscopic guidance in adults and children.

• Occasionally, an imaging study such as MRI, CT scan, or plain x-ray film helps in diagnosing laryngeal lesions that might require stenting or in defining the length of stenosis or malacia in the trachea.

The criterion standard for evaluating the larynx and trachea is direct laryngoscopy and bronchoscopy. Using these tools, the segment that requires stenting can be defined.

Graft vascularization

Most histological studies have been performed in animals. Concern has been raised that a stent could cause impaired lumen healing, increasing the complication rate; however, a study on 36 white rabbits that had tracheoplasty with autologous cartilage grafting with and without stents showed the rate of vascularization of the graft was equal among both groups and possibly slightly superior in the stented group at 10 days following insertion.

Mucociliary transport

The laryngotracheal mucociliary transport in guinea pigs with and without stenting was evaluated in studies conducted in 1997 and 2000 by S.Y. Lee of the Department of Otolaryngology, Taiwan University, Taiwan. In these studies, stenting appeared to preserve or increase the mucociliary function of laryngotracheal mucosa in the acute phase of stenting compared to mucosa without stenting. ^{[7, 8]}

Tracheal stents

Histological evaluation has been accomplished with metal, silicone, and bioabsorbable stents.

For metal stents, the most common (eg, Palmaz stent) are placed intraluminally and are expanded with a balloon. One study reported that the stent was overgrown with tracheal epithelium; granulation tissue formation was the only complication cited. In experimental studies in cats, histological analysis revealed a mild inflammatory reaction with granulation tissue present in all animals in which the stent was not manipulated. When the stent was overexpanded, the reaction was more severe; epithelial ulceration that had sealed the lumen in most animals was noted.

In the same study, researchers opened and closed cats' tracheas with or without stent placement. Increased inflammatory reaction, granulation tissue, and epithelial damage were observed in animals with stents as opposed to control subjects without stents. Based on that study, the Palmaz stent, when used in a normal trachea on which an operation has not been performed, provokes only a very mild and clinically insignificant inflammatory reaction when appropriately expanded. However, once surgery has been performed on the trachea, the inciting inflammatory reaction can cause formation of granulation tissue.

A study from Japan examined expandable metallic stents after tracheal patch reconstruction with omentoplasty. Polypoid granulation tissue developed at both ends of the metallic stent. Histologically, epithelium was regenerated in the patched area 4 weeks postoperatively; the patched area was covered with respiratory epithelium 12 weeks postoperatively. ^[9]

Another study investigated the histocompatibility of 4 different types of material used to cover expandable Gianturco metallic stents in dogs: polypropylene mesh, silicone-covered mesh, polyester mesh, and expanded polytetrafluoroethylene. The polypropylene mesh appeared to be the most biocompatible of all the coverings and was histocompatible to the airway. ^[10]

For bioabsorbable and silicone stents, a comparison of bioabsorbable airway stents, shown in the images below, with a silicone airway stent and metallic stent was performed in Finland on rabbits.

Intraoperative picture showing a solid dissolvable airway stent next to a trachea in a 3-kg New Zealand white rabbit.

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Solid spiral dissolvable stent produced for the trachea of a rabbit. Scale is in centimeters.

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The bioabsorbable spiral stent was manufactured with self-reinforced poly-L-lactide material, and tracheomalacia was created by extramucosal resection of cartilaginous arches of the cervical trachea. Hyperplastic polyps occurred at both ends of the silicone stent, and the internal diameter of the stent became encrusted. The bioabsorbable stent and the metallic stents were tolerated well.

Other experimental studies have been performed to evaluate histological events that occur when a bioabsorbable stent is placed, as compared with silicone stents. Silicone stents in one animal study again showed a tendency to become stenosed with encrusted material and to develop a hyperplastic bulge at both ends. Bioabsorbable stents of poly-L-lactide material showed no foreign body reaction and had a tendency to penetrate into the tracheal wall. These stents had been reabsorbed at 10-month follow-up.

An immersion study by Perkins et al indicated that poly(lactic-co-glycolic) acid (PLGA) and poly(ester urethane) urea (PEUU) provide good corrosion protection on magnesium alloy tracheal stents, as demonstrated by a reduction in magnesium ion concentrations when these coatings were used. ^[11]