Laryngeal and Tracheal Stents

Anatomy and Physiology

Larynx: The larynx is a cartilaginous structure located above the trachea and below the hyoid bone. It comprises three cartilages, namely thyroid, cricoid, and a pair of arytenoid cartilages. The larynx's function is to help control the flow of air in and out of the lungs, prevent food and water from entering the lungs, helps in swallowing, and acts as the main source of speech.

A laryngeal stent is placed through and above true or false vocal cords or far below the true vocal cords to avoid scarring, granulation tissue, and stent failure if placed immediately below true vocal cords.

Trachea: The fibrocartilaginous structure of the lower respiratory tract below the larynx is the trachea. It forms the main trunk of the tracheobronchial tree. The trachea is made of 16 to 20 tracheal cartilages anteriorly and tracheal muscles posteriorly. The function of the trachea is to transport air in and out of the lungs. 

Laryngotracheal stenosis is graded based on the percent of obstruction:

Cotton Myer subglottic stenosis grading scale:[5]

Indications

There are many congenital and acquired conditions in which laryngeal and tracheal stents are required. These indications are as follows:

• Reconstruction of laryngotracheal stenosis 
• Trauma to larynx 
• Congenital anomalies of larynx and trachea
• Malignancy of larynx and trachea 
• Laryngeal web or atresia 
• Tracheomalacia and bronchomalacia[6]

Contraindications

Absolute contraindications to laryngeal and tracheal stents include:

1. Patients who are medically unstable for general anesthesia
2. Patients who are allergic to stent material
3. Absence of expandable lung distal to the obstruction

Relative contraindications include:

1. High chances of the poor outcome despite stenting
2. Increased risk of complications

Equipment

Types of Stents

Different stents are used for different indications; the common types and their uses are as follows:

Laryngeal Stents

These are used only for glottic or subglottic stenosis and can be either short term (less than six weeks) or long term (more than six weeks).[7]

• Short term stenting is usually used to stabilize cartilaginous graft following a reconstruction surgery of larynx or trachea, or post-trauma or for laryngeal web or atresia. The common stents used are:
• Aboulker stents
• Silicone stents
• Montgomery laryngeal stents
• Endotracheal tubes and
• Laryngeal keels. 
• Long term stenting is used when the trachea above the tracheostomy tube requires stenting from either collapse or stenosis. The common stents used is Montgomery T-tube, or a long Aboulker stent is wired to a metal tracheostomy tube and wired into the trachea.[8]

Aboulker Stent

• The most commonly used stent in children after laryngotracheal reconstruction surgery.
• It is a cigar-shaped prosthesis in different diameters at a length of 120 mm. 
• Low incidence of granulation tissue formation or irritation.
• It is most effective in counteracting scar contracture and preventing the collapse of the lumen after reconstructive surgery.

Montgomery Stent

• It is made of silicone material and has a long center lumen with a smaller lumen projecting from the side at a 75° or 90° angle.

Silastic Sheet

• First used by Evans in 1977 for laryngotracheoplasty. 
• Since it applies pressure to the mucosa, granulation tissue formation chances are high, so a Teflon Aboulker stent has replaced it.

Endotracheal Tubes

• Made of polyvinyl chloride and has been used in the laryngotracheal area.
• They are associated with a high incidence of fibrosis, inflammation, and granulation tissue after four weeks.
• These stents should be used for procedures involving four weeks or less to prevent complications.

Silicone Stents

• Mainly used in adults and are placed in the larynx.
• Common complication from this stent is vocal cord edema, stent migration, and restenosis after removal.

Metallic Stents

• Made of bare metal or coated with silicone, nylon, or polyurethane.
• It can be placed in an outpatient setting using flexible bronchoscopy under local anesthesia.
• Higher incidence of granulation tissue and irritation and are difficult to remove.
• It should not be used for benign airway disorders and has an FDA black box warning.

Preparation

Work up for laryngeal and tracheal anatomy must include a direct laryngoscopy or bronchoscopy in the operating room. Imaging studies such as MRI, CT scans may be required to help diagnose laryngeal lesions that might require stenting or in defining the length of stenosis or malacia in the trachea. 

Preoperative preparation for placement of laryngeal or tracheal stents include:

• Requires a tracheotomy to maintain airway during the procedure 
• Supplemental materials for neck incision
• Suture material either 4-0 or 3-0 proline to secure the stent
• Stents of different sizes for different airways sizes, availability of fluoroscopy sometimes if stents are placed to correct airway obstruction

Consent for surgery must be obtained, and the risks, benefits, and alternatives must be clearly explained to the patient.

Technique or Treatment

Once radiographic findings suggest central airway obstruction, bronchoscopy should be performed to visualize the airway directly. Once the obstruction is noted, the degree of obstruction or length and diameter of the stricture must be noted.

The technique for insertion of a metallic stent in trachea: Metallic stents are usually preferred for tracheobronchial pathology. The most common way of insertion involves general anesthesia, rigid bronchoscopy, and direct endoscopic visualization, as this process helps in accurate and rapid placement of the stent. Before performing stenting using rigid bronchoscopy, an inspection of the airway with flexible bronchoscopy is performed. The narrowed airway is sometimes dilated for easy delivery of the stent. The stent delivery device can be used directly or passed over a guidewire. The scope is withdrawn proximally to confirm the appropriate placement of the stent.

If a stent is placed using flexible bronchoscopy, airway lumen is maximized using balloon dilation or debulking of the tumor, and a stent delivery device is passed over a guidewire, which is then verified bronchoscopically or sometimes fluoroscopy is used.[9] After deployment, it takes at least 24 to 48 hours before the stent completely enlarges and reaches the final dimension. A chest radiograph is performed to verify the satisfactory location.

Complications

The complication that is caused by any laryngeal stents include:

• Formation of granulation tissue
• Scar tissue formation
• Broken stent 
• Stent associated infection 
• Stent migration 
• Dysphagia and aspiration 

The complications from tracheal stents are unusual, but stent migration occurs in about 31% of cases in a study by Russ et al. after a 10-month follow-up. Metallic stent fracture, erosion of stent leading to massive hemoptysis can occur. The incidence of granulation tissue is noted to be 15 to 20%. Metallic stents sometimes get incorporated into the mucosa and can be very difficult to remove.

Clinical Significance

Laryngeal and tracheal stents are primarily used for the postoperative period to support airways after reconstructive surgery. They are also commonly used as palliative care measures in patients with end-stage airway disease or lung malignancies and inserted mainly by interventional pulmonologists in these patient populations. Experience and knowledge of a surgeon or a provider are crucial in deciding to use a laryngeal or tracheal stent and stent type. 

No proper guidelines exist to guide in deciding the type and material of the stent. The future insight should focus on developing an ideal stent capable of maintaining a patent airway, being available in different sizes, expanding, having no complications, and causing minimal tissue reaction.

Enhancing Healthcare Team Outcomes

The placement of laryngeal and tracheal stents must be carefully evaluated by a multidisciplinary team involving an otolaryngologist, interventional pulmonologist, and palliative care team. Careful selection of patients should be made, and the benefit of placing a stent must be weighed against risks. The selection of the type of stent depends on the surgeon or provider's experience and patient problem. There is a lack of specific guidelines for the type of stent to be used and placement methods. Future studies are required to develop an ideal stent that should have the attributes of easy to insert and remove and cause fewer complications.