cardiac arrest, and death. A report of forceps debulking of granulation tissue led to subsequent loss of tissue into distal trachea, further airway obstruction, subsequent hospital complications, and eventually the child’s death [48]. Other reports exist of excessive bleeding after granuloma debridement leading to uncontrollable airway hemorrhage and subsequent asphyxiation [57].

Endobronchial Airway Stents

Endobronchial airway stents are commonly utilized for palliation of CAO and come in multiple different formulations, con gurations, and sizes. Similar to the adults, CAO improvement is commonly reported in pediatric series. While stents can often make immediate impacts to respiratory status, this potential bene t must still be considered in the long-term management plan of the patient’s underlying problem. There are also well-documented long-term complications associated with stent placement; therefore it remains paramount that one should never sacri ce long-­ term options such as a potential curative surgical resection over short-term gains. Patients should be evaluated and managed in a multidisciplinary fashion with experts in CAO and pediatric airway disease.

The indications for airway stents in pediatric patients are quite different from their adult counterparts. Most cases requiring stenting of the airway in children are related to congenital or iatrogenic airway malacia or stenosis, and more rarely can be related to neoplasms of the thorax [58]. The ideal pediatric airway stent would be easy to place in relatively small airways, provide structure to the airway, have minimal adverse effects, and be removable at any time or unnecessary to remove (grow with the patient as the airway diameters increase). Currently, there is no such stent. Therefore, the placement of these endobronchial stents should not be taken lightly as serious long-term complications can arise, especially in patients with non-malignant CAO. Additionally, while rare, stent-related morbidity/mortality has been reported for almost all airway stents [59, 60].

Airway stents can be divided into different categories based on the material content of the stent. We have therefore divided this topic into three different categories: metallic, silastic, and novel stents.

Metallic Stents

Metallic stents can be easier to place, including with the use of fexible bronchoscopy and/or fuoroscopy (Fig. 38.8). As airway caliber can be a signi cant limitation in infants and young children, the ability to place a small stent over a guidewire under fuoroscopy is potentially attractive [61].

Two types of metallic stents are available: bal- loon-expandable and self-expanding; however, no metallic stents are currently approved by the Food and Drug Administration (FDA) for pediatric use. The only FDA-­approved metallic airway stent is the Merit Aero (Merit Medical Systems, South Jordan, UT, USA). They are self-expand- able metal stents (SEMS) with a polyurethane coating and constructed from nickel-titanium (Nitinol). Current stent size diameters range from 6 mm to 20 mm. Over the years, Aero SEMS have been modi ed and many are able to be placed over a wire or over a bronchoscope, or the new smaller stents (6 × 10 mm and 6 × 15 mm) are able to be placed through the bronchoscope. The currently available balloon-expandable metallic stents are often designed for vascular or cardiac purposes but have been reported for airway use in the literature. The best described balloon-expand- able stent in pediatrics appears to be the Palmaz (Cordis Corporation, Miami Lakes, FL, USA). Designed as a vascular stent made of stainless steel, it is likely popular due to the available small dimensions and ease of placement. Palmaz stent sizes range from 5 mm to 10 mm in outer diameter [50]. Intrastent (IntraTherapeuticsInc, MN, USA) additionally offers similar-sized stents and has the advantage of magnetic resonance imaging (MRI) compatibility and retrievability [62].

Complications of stent placement are well described, with granulation tissue and migration being described as the most common. Recurrent granulation tissue can be managed with serial dilation procedures and/or debulking of excess

Fig. 38.8  Placement of self-expandable metal stent (SEMS) into left mainstem bronchus. (a) Bronchoscopic view of left mainstem obstruction. (b) After partial deb-

ulking of left mainstem lesion, signi cant extrinsic compression remained, therefore a 10 × 30 mm SEMS was placed with excellent restoration of airway patency

tissue [60, 63]. Excessive granulation tissue may also be colonized with pathogenic organisms, potentially increasing bacterial overgrowth concerns, especially in smaller airways (i.e., infants) [41, 64].

The re-epithelialization of metal stents within the airway has remained a concern, including a black box warning by the Federal Drug Administration in 2005 [65]. Some patients have experienced airway growth within stents, preventing endoscopic removal, leading to fracture with retained metal, then requiring surgical intervention/resection [63]. The largest concern related to the SEMS placement remains the documented episodes wherein patients who likely had surgical correctable disease (i.e., subglottic stenosis curable by short-segment tracheal resection), however, subsequently became inoperable due to metallic stent-related complications [66]. Despite these potential complications, some believe that in appropriate situations, given the potential size options, SEMS remains appropriate [67].

As time has allowed some longitudinal follow- ­up, studies have described the longer-term out-

comes of SEMS in pediatrics. One study of 146 SEMS placed in 87 children with 9.4 ± 6.7 years of follow-up demonstrated clinical improvement in all but two of the patients [62]. Another study of 41 SEMS in 24 infants showed gradual and signi cant expansion of stents after placement, illustrating the potential advantage of expandable metallic stents in the pediatric airway—the ability to be further expanded in the still growing lumen [68].

Silastic Stents

Silicone stents are currently available in multiple sizes and con gurations. Silicone stents require rigid bronchoscopy for placement (Figs. 38.9 and 38.10), which may be more challenging in smaller airways. The smallest commercially available silicone stent in the United States is of 6 mm. Potential advantages of silicone stent placement include the inert properties of silicone. As a result, they have the potential for removal after long in situ durations. However, complications (similar to stents in general) include granulation, stent migration, and mucus impaction.

Fig. 38.9  Silicone stent placement for non-malignant disease. (a) Recurrent tracheal stenosis after surgical resection/reconstruction for tracheal stenosis prompted placement of endotracheal silicone stent. Endoscopic view of proximal end of tracheal silicone stent placement dem-

onstrating preserved airway caliber. (b) Bronchoscopic view from within a Y-stent placed for tracheobronchomalacia. The left mainstem entrance is at the 10 o’clock position and the right mainstem entrance is at the 4 o’clock position

Another potential drawback is that the inner to outer diameter ratio is greater than metallic stents and therefore may occupy more diameter of the airway. A long-term advantage of silastic stents is that they are non-expanding and will not develop fatigue fracture of the stent wires. Reports of successful cases are feasible in infants; however, poor results have been associated with high-­ pressure vascular compression [69].

Novel Stents

Absorbable or biodegradable stents remain attractive within the realm of pediatric airways; however, they are unavailable for use within the United States. Biodegradable stents could remain within the airway for a nite time without the need for additional removal procedures. Similar stents are being utilized in some disciplines: urethral, biliary, and vascular; however, data within the airway could dramatically modify airway

plans for children as they continue to grow. One promising technology appears to be Polydioxanone stents, which are composed of semi-crystalline, biodegradable polymers. They have initial shape memory, but later will degrade by random hydrolysis of its ester bonds. Small case series suggest 15 weeks for complete absorption while in an animal model 10 weeks were needed for degradation [70]. European data suggest that polydioxanone stents are likely both safe and ef cacious in infants with severe tracheobronchial obstruction. They also describe fewer complications than traditional stents and the biocompatibility remains a great advantage. Longer-term durability and cost issues remain unclear as admittedly rapid stent degradation may necessitate repeat stenting. Therefore, additional consideration of cost–bene-t in absorbable vs traditional stenting will likely be needed keeping patient age, pathology, and provider experience in mind [58].