Historical Perspective

Early in the evolution of tracheal surgery, it was believed that the amount of trachea that could be excised safely was four rings or approximately 2 cm. Because of this belief, much of the early work in this area focused on the use of prosthetics for tracheal replacement. Although early clinical reports of tracheal replacement with bioengineered materials have been reported,^1,2 consistent success is not yet attained for replacement of the airway.

In parallel with the efforts to find a suitable prosthetic device, efforts were underway to determine the possibilities of resection and primary reconstruction. Grillo and colleagues³ systematically investigated the limits of resection of the trachea that might permit primary reconstruction without excessive tension and without destruction of its vital blood supply. Experiments in human cadavers demonstrated that the blood supply of the trachea entered in its lateral pedicles and that mobilization of the trachea is best accomplished only by anterior and posterior dissection. These studies concluded that a median length of 4.5 cm or approximately seven rings could be resected and primarily reconstructed with an acceptable amount of tension.

As the issues of extent of resection, methods of mobilization, limits of acceptable tension, and preservation of blood supply were established, primary resection and reconstruction became the accepted mode of managing most diseases that involved the trachea. Reports of resection and primary reconstruction of lengths of the trachea followed, which had been previously thought to be impossible.^4,5

Anatomy

The adult trachea measures 11 cm in average length from the anterior border of the cricoid cartilage to the carinal spur. There are 18 to 22 cartilaginous rings in the human trachea, with approximately two rings per centimeter. The only complete cartilaginous ring in the normal airway is the cricoid cartilage of the larynx. The remainder of the rings is C-shaped, connected posteriorly by the membranous portion of the trachea. The blood supply of the trachea is shared with the esophagus laterally and with the main bronchi below. Above, the blood supply originates from the inferior thyroid artery, and vessels to the lower trachea are derived from the bronchial vessels (Fig. 8-1). Importantly, branches of these vessels enter the trachea laterally.

Congenital Lesions

Congenital tracheal stenosis may present as a web-like diaphragm, most often at subcricoid level. More lengthy stenoses may involve the entire trachea, sometimes with a normal larynx and main bronchi, or they may involve variable lengths of the trachea (Fig. 8-2). Funnel-like narrowing is sometimes seen, with gradual narrowing to the stenotic segment. Segmental stenosis of the lower trachea may be accompanied by bronchial anomalies such as origin of all or part of the right upper-lobe bronchus from the trachea just above the stenotic segment. Most often the cartilaginous rings are circular in the area of stenosis. Other developmental anomalies may occur in a patient with congenital tracheal stenosis.

Trauma

External Trauma

The trachea, carina, and main bronchi may be damaged by either blunt or penetrating trauma. Blunt cervical injury may result in injury to the airway at any level from the hyoid bone to the carina.⁶ Subcutaneous emphysema may be detected in the neck or, if the injury involves the more distal trachea, pneumomediastinum may be seen. Pneumothorax may result from tracheal injury within the chest cavity. Patients may present with varying severities of dyspnea from airway obstruction caused by these injuries or from tracheal transection. A patient with an initially satisfactory airway may rapidly decompensate while under observation or as intubation or examination of the airway is attempted.

If the airway is partially separated, a flexible bronchoscope with an endotracheal tube threaded over it is the best way to assess it. If difficulty is encountered, emergency tracheostomy should be quickly performed before the airway is lost. A completely transected trachea may retract into the mediastinum but is easily located by finger palpation and grasped by clamps and delivered into the field.

Blunt intrathoracic tracheal injury is a result of high-impact trauma, and as a result, it is usually associated with concomitant chest wall, pulmonary, and great vessel injury. Injuries to the carina and the main and lobar bronchi may occur from crush injuries to the chest. These tend to occur more frequently than tracheal injuries.

Inhalational Injuries

Tracheal injury may also occur in the form of thermal or chemical damage by inhalation. Inhalation burns of the larynx, trachea, and bronchi may be particularly difficult injuries. The degree of inflammatory change, granulation tissue response, and scarring will depend on the depth of mucosal injury. In most cases, the tracheal rings are not destroyed. Resection is generally precluded, as lengthy injuries often occur. A number of cases of airway obstruction caused by burns have been managed initially by a tracheostomy placed at the second or third ring, typically within the area of burn injury, followed later by placement of a silicone T tube to span the injured area.

Iatrogenic Injuries

Acute Intubation Injuries

Lacerations of the trachea during intubation occur most often in the membranous wall. These may be long and may also damage the esophagus, resulting in a tracheoesophageal fistula (TEF). Respiratory symptoms and concomitant esophageal injuries are indications for immediate repair.

Postintubation Injuries

Postintubation injuries to the trachea include granulomas, strictures, malacia, and tracheoesophageal and tracheoinnominate artery fistulas (Fig. 8-3).

Tracheal strictures represent the most common postintubation injuries. These occur principally at either the level of the tracheal stoma or that of the tracheal cuff. Both result from proliferative and cicatricial responses to tracheal injury. Granulomas result from erosion by the tip of a tracheostomy or endotracheal tube and can also occur at the site of a healed tracheostomy. Stomal stenosis results from the gradual enlargement of a tracheal stoma and its eventual healing by contraction. This pulls the sides of the defect together, distorting the tracheal lumen to a triangular configuration with the base of the triangle located posteriorly, consisting of the uninjured membranous wall. The instigating large stoma may result from overzealous excision of tracheal wall at the time of the initial tracheostomy, from erosive infection around the margins of the stoma, or most commonly from erosion secondary to leverage by equipment attached to the tracheostomy tube during ventilation. The stenotic process may extend into the subglottic larynx if the previous tracheostomy was placed inappropriately high in the trachea.

Cuff stenosis, on the other hand, is caused by circumferential erosion of the trachea by excessive pressure exerted by the sealing cuff. In the healing process, cicatricial connective tissue is formed, which contracts in a circumferential fashion. The route of entry of the ventilatory tube does not affect the occurrence of cuff injury, only its level. These lesions are seen in patients who have had only endotracheal intubation as well as those with previous tracheostomy. Cuff injuries have been observed in patients with only 48 h of exposure to a high-pressure cuff.⁷ However, since the length of exposure increases the risk of injury, these lesions are seen more frequently in patients after prolonged ventilation.

The development of the large-volume, low-pressure cuff for tracheostomy and endotracheal tubes for ventilation has greatly lowered the incidence of cuff stenoses. However, since the compliance curve of the plastic from which these cuffs are made is unsatisfactory when the cuff is inflated beyond its normal filled volume, pressure rises rapidly with additional filling. Therefore, overinflation of these cuffs converts them to high-pressure cuffs. This fact leads to a continued incidence of cuff stenosis.

Malacia of the trachea rather than stenosis may also occur at the level of cuff injury. The mucosa generally reveals squamous metaplasia in contrast to the scar tissue seen in the stenotic lesion. It is not clear why some patients develop malacic lesions rather than stenosis. Areas of malacia can also be seen between the level of a tracheal stoma and a cuff stenosis.

TEFs occur most often in patients who have an infected cuffed tube in the trachea for a long period of time concomitant with a nasogastric tube in the esophagus. These may represent large fistulas that can extend from one cartilaginous margin to the other. In most cuff fistulas, there is a circumferential injury to the trachea at the level of the fistula. Smaller fistulas are occasionally seen, which may be related to the tip of the tube pointing against the membranous wall. These variations must be considered in surgical repair.

Anterior injuries of the trachea may lead to the development of tracheoinnominate artery fistulas. These are most often due to direct erosion of the inner elbow of the tracheostomy tube in an inferiorly placed stoma. Placement of the tracheal stoma at the conventional level of the second or third tracheal ring prevents these fistulas.

Radiation therapy can produce late stenosis of the larynx and trachea. Because of the intrinsic damage to these tissues, surgical repair is hazardous. Tracheal stenosis due to irradiation may be treated with T-tube placement or carefully considered reconstruction with omental transfer to augment healing in select patients.⁸

Idiopathic Laryngotracheal Stenosis

A minority of patients present with stenosis of the airway at various levels without history of trauma, infection, inhalation injury, or airway intubation. This diagnosis is one of exclusion and is characterized by an inflammatory cicatricial stenosis at the level of the subglottic larynx, cricoid, and upper trachea. An overwhelming majority of these patients are female and typically present with signs and symptoms of upper airway obstruction.⁹ This process is confined intrinsically to the wall of the airway and the immediately surrounding connective tissue. Histology shows extensive fibrosis, acute and chronic inflammation, and dilation of mucus glands with relatively normal cartilage.¹⁰ All patients should be screened for connective tissue disorders and Wegener’s granulomatosis by serum ANA and ANCA.

It is impossible to predict the future course of the disease. The presence of active inflammation is best treated by serial dilation until the inflammatory process subsides. When airway obstruction becomes severe and does not respond for sufficiently long intervals to dilatation, surgery is indicated. Patients are best treated with definitive single-stage laryngotracheal resection and primary reconstruction.⁹ The goal of reconstruction is removal of all of the scarred tissue and reconstruct with healthy tissue.

Tracheobronchomalacia

Acquired tracheomalacia may result from postintubation injury. However, in patients with chronic obstructive pulmonary disease, malacia may develop in the lower trachea, main bronchi, and sometimes the more distal bronchi in the absence of prior intubation. When the patient attempts to expire or to cough, the membranous wall approximates to the anterior, softened cartilaginous wall, causing nearly total obstruction. Consequently, the posterior membranous wall elongates and becomes redundant. It is possible to ameliorate the deformity by pulling the ends of the cartilages toward one another posteriorly, restoring a more circular shape to the airway. The redundant membranous wall must be tacked to the posterior splinting material to prevent it from falling forward into the lumen. Various materials have been used for splinting, none with complete success. These have included fascia lata, pericardium, lyophilized bone, polytetrafluoroethylene, and rigid plastic splints. We currently use sheets of polypropylene mesh to plicate the membranous wall as described by Rainer.¹¹

Tracheal Tumors

Primary tracheal tumors are rare. It is estimated that tracheal tumors occur in about 2.7 new cases per million per year.¹² The rarity of these tumors and their often insidious presentation frequently lead to a delay in diagnosis and inappropriate treatment until the definitive diagnosis is made.

Tumor Classification

About two-thirds of primary tracheal tumors are of two histologic types: squamous cell carcinoma (SCC) and adenoid cystic carcinoma (ACC), formally known as “cylindroma.” These two types occur with equal frequency. The remaining third of the tumors are widely distributed in a heterogeneous group, both malignant and benign. A variety of secondary tumors involve the trachea. These include carcinomas of the larynx, thyroid, lung, and esophagus. Rarely, tumors may metastasize to the submucosa of the trachea or to the mediastinum, with secondary invasion of the trachea. Thus, carcinoma of the breast and mediastinal lymphoma may invade the trachea.

SCC may be either exophytic or ulcerative. It may also be multiple and extend over a considerable length of trachea. The tumor metastasizes to the regional lymph nodes and, in its more aggressive and late forms, invades mediastinal structures. In general, its progress appears to be relatively rapid in comparison with that of ACC. A number of these patients have returned with a second SCC of the lung or oropharynx. SCC occurs predominantly in men, usually cigarette smokers.¹³

ACC often has an indolent course, frequently eluding diagnosis for years. Tumor recurrence may occur years after surgical resection. ACC may extend over long distances submucosally in the airways and also perineurally. It spreads to regional lymph nodes, although less frequently than SSC. Although it may invade the thyroid or muscular coats of the esophagus by contiguity, ACC frequently displaces mediastinal structures before actually invading them. Metastases to the lungs are not uncommon. These may grow very slowly over a period of years and remain asymptomatic until they become quite large. Metastases to bone and other organs can also occur. In contrast to tracheal SSC, men and women are equally affected and there is no clear association with tobacco smoke exposure.¹²

The group of tumors other than SCC and ACC, although representing only about one-quarter of the population, is composed of a multitude of tumor types and varying degrees of malignancy, including both epithelial and mesenchymal neoplasms. This list includes pleomorphic adenomas, leiomyomas, chondromas, carcinoid tumors, mucoepidermoid tumors, and sarcomas.

Secondary tumors involving the trachea should be briefly noted. Both papillary and follicular carcinoma of the thyroid and mixed varieties of the two may invade the trachea primarily, usually at the level of the isthmus.¹⁴ Invasion of the trachea by thyroid carcinoma is best managed by resection with airway reconstruction. Localized extension of tumor may also require partial esophageal resection or radical resection, including laryngectomy with mediastinal tracheostomy. More commonly, invasion is seen after thyroidectomy for carcinoma, in cases where surgeons were aware that they were “shaving off” the tumor from the trachea. In such cases, concurrent or early resection of the involved trachea should be considered.

Patients with pathologic lesions of the trachea usually present with signs and symptoms of upper airway obstruction: dyspnea on exertion, wheezing, stridor, and obstructive pneumonia. The most common presentation, wheezing and dyspnea on exertion, is frequently misinterpreted as adult-onset asthma. It is not uncommon for the symptoms in these patients to become progressively worse and correspondingly be treated with corticosteroids before the correct diagnosis is finally made. It should be a diagnostic rule that any patient who presents with such symptoms and has been intubated and ventilated must be considered to have organic stenosis unless proven otherwise.

Tumors of the trachea may also present insidiously. Their most common signs and symptoms are cough (37 percent), hemoptysis (41 percent), and the signs of progressive airway obstruction, including shortness of breath on exertion (54 percent), wheezing and stridor (35 percent), and, less commonly, dysphagia or hoarseness (7 percent).¹² Signs and symptoms may vary with the histology of the tumor. Hemoptysis is prominent in patients with SSC and usually leads to earlier diagnosis. ACC more commonly presents with wheezing or stridor as a predominant symptom, often leading to delay in diagnosis. In one study, the mean duration of symptoms prior to diagnosis in patients with SCC of the trachea was only 4 months, whereas in those with ACC, it was 18 months.¹⁵

Among nonintubated patients, TEF is manifest by episodes of choking while swallowing, suctioning of food or beverage from trachea, or an increase in tracheal secretions. Among intubated patients, there may be gastric distention or loss of delivered tidal volume. Tracheoinnominate arterial fistulas are rare but may be announced by a premonitory hemorrhage. In treating bleeding from a tracheostomy, it is important to differentiate between erosion of tracheal granulations or mucosa and arterial fistula. Any suspicious hemorrhage from a tracheal stoma should be immediately investigated.

Radiographic Assessment

Definitive diagnosis of airway problems is often delayed because of an apparently normal chest radiograph. Closer inspection will often reveal abnormality of the tracheal air column. Lesions can frequently be seen on overpenetrated views or tomograms of the larynx and trachea. The location of the lesion, its linear extent, extratracheal involvement, and the amount of airway uninvolved can be determined. Lateral neck views, using soft tissue technique with the patient swallowing and the neck hyperextended to bring the trachea up above the clavicles, are useful to define pathology in the upper trachea. Fluoroscopy not only demonstrates functional asymmetry of the vocal cords if present but may also give additional information about the extent of the lesion and collapse of the airway if malacia is present. In some cases, polytomography (AP and lateral views) gives additional detail, particularly of mediastinal involvement. Computed tomography (CT) offers little overstandard radiologic techniques for benign disease but is especially helpful in malignant disease to assess extramural extent and enlarged lymph nodes. A combination of inspiratory and expiratory images from a CT is currently the easiest and most accurate noninvasive method of diagnosing tracheomalacia.¹⁶ The exact role of magnetic resonance imaging (MRI) is yet to be defined. Sagittal and coronal views, however, have been helpful in certain cases and may provide more accurate detail than standard radiographic techniques.

Bronchoscopy

Certainly the role of both flexible and rigid bronchoscopy in the diagnosis of tracheal pathology cannot be overstated. Biopsy specimens of both benign and malignant lesions of the trachea are made with these techniques. In planning surgical resections, bronchoscopy is invaluable. Definitive assessment of the airway is performed by meticulous endoscopic measurements with a rigid bronchoscope. Measurement of the carina, bottom of the lesion, top of the lesion, and level of the vocal cords will determine the extent of the disease process and likelihood of reconstruction. At the time of bronchoscopy, it is important to assess the adequacy of the larynx and degree of inflammation of the mucosa.

Airway Management and Endoscopy

Crucial to the management of all problems of the trachea is the ability to control the airway. Tracheal trauma, tumors, and postintubation stenosis may present with acute airway obstruction. Endotracheal intubation may be impossible and even dangerous, especially in patients with high tracheal lesions. Simple maneuvers to elevate the head of the patient, administration of cool mist, oxygen, and careful sedation may allow control of the airway to be accomplished in a semielective manner. Control is best accomplished in the operating room, where an assortment of rigid bronchoscopes, dilators, biopsy forceps, and instruments to perform emergency tracheostomy are available. Anesthesia, as in elective tracheal operations, is best accomplished by inhalation technique to allow spontaneous ventilation.¹⁷ Muscle-relaxing agents should not be used to avoid the lethal combination of airway obstruction and an apneic patient.

Initial evaluation should be performed with a rigid bronchoscope carefully inserted through the vocal cords, stopping just proximal to the level of obstruction. This can be passed beyond most tumors, even those causing nearly total obstruction. Once the status of the distal airway has been assessed, the tumor can be partially removed with biopsy forceps to determine its consistency and vascularity. For most tumors, the tip of the rigid bronchoscope can be used to core out most of the tumor.¹⁷ The tumor can then be grasped with biopsy forceps and removed. If bleeding ensues, the bronchoscope may be passed into the distal airway for ventilation, and this will also serve to tamponade bleeding.

Postintubation stenoses pose a slightly different problem in airway control. Bronchoscopy is invaluable in determining the extent of airway involvement and, just as importantly, the amount of uninvolved airway. Measurements as accurate as possible should be recorded. The quality of the mucosa should be carefully assessed. Marked inflammation and erythema may dictate delay of definitive surgical correction to a time when this has subsided. Both flexible and rigid bronchoscopes are used in these situations.

Caution must be taken with flexible bronchoscopy in the assessment of critical airway stenosis. The flexible bronchoscope may precipitate airway obstruction in patients with critical stenoses by increasing secretions or causing bleeding or edema. If the physician performing the endoscopy is unprepared to dilate the patient emergently, lethal airway obstruction may occur. Whenever severe airway stenosis is encountered, it is best not to manipulate the stenosis with the flexible bronchoscope. Proper evaluation should be performed in the operating room with facilities available to dilate the stenosis if necessary. In nonemergent cases, endoscopy is best performed as part of the planned surgical procedure.

As a general rule, the rigid bronchoscope is much more valuable in assessing airway pathology. Attempting to pass a large rigid bronchoscope beyond a tough, inflammatory stricture may be impossible, may result in tracheal rupture, or may cause total airway obstruction secondary to bleeding or edema. Jackson dilators passed through the rigid bronchoscope under direct vision and an assortment of graduated rigid bronchoscopes can be used to serially dilate postintubation and idiopathic strictures. By gradually dilating these tight, rigid strictures, the risk of perforation and bleeding is minimized. Racemic epinephrine and steroids are often used for 24 to 48 h to minimize subsequent reactive edema.

It is important to understand that dilation or endoscopic removal of malignant or inflammatory strictures is often only a temporizing measure. In the case of inflammatory stricture, restenosis usually develops within days to weeks. The use of these techniques in emergent situations allows more thorough evaluation of the patient and enables surgery to be performed electively. Many patients are on corticosteroids at the time of presentation and, by improving the airway, these may be tapered and discontinued. This will enable the operation to be performed at a later time without the threat of impaired healing.

The above maneuvers are also used in an elective operation when the patient has presented with a narrowed but not critical airway. Dilation with rigid bronchoscopy permits assessment of the distal airway, placement of an endotracheal tube, and provision of an adequate lumen to prevent carbon dioxide accumulation early in the procedure.

Tracheostomy may be necessary in some patients as the only method to secure an airway. If feasible, this should be placed through the most damaged portion of the trachea to preserve the maximal amount of normal trachea for subsequent reconstruction. If tracheostomy is contemplated at the completion of tracheal resection, which is rarely necessary, it should be placed at least two rings away from the anastomosis. The anastomosis should then be protected with the thyroid gland or strap muscles to avoid contamination of the suture line. This will lessen the likelihood of subsequent dehiscence or stenosis. A tracheostomy tube should never be placed through an anastomosis.

Surgical Therapy

Anesthesia

Anesthesia for tracheal reconstruction, especially where there is a high degree of airway obstruction distally, is best administered by inhalational agents.¹⁷ A slow, patient induction may be necessary if there is a high degree of airway obstruction. This is preferable and safer than paralysis of respiration with a consequent urgent need to establish an airway.

The surgeon should be available with an array of rigid bronchoscopes from pediatric to adult sizes as the induction commences. The residual airway through which the patient is breathing may measure as little as 2 or 3 mm in diameter. In most cases, tumors are not circumferential. After bronchoscopy, a small endotracheal tube can often be insinuated past a highly obstructive tumor. In other cases, the tube is left above the tumor. This contrasts with the circumferential stenoses seen in some inflammatory lesions. In rare cases, it may be necessary to resect portions of tumor with biopsy forceps to enlarge the channel for passage of a tube.