Keywords

Tracheal injury (TI) is a rare event with potentially life-threatening consequences mostly represented by mediastinitis and resultant sepsis. TI can be the classified as traumatic from both blunt and penetrating injury or iatrogenic when it occurs during surgery, endotracheal intubation, or other operative endoscopic procedure approaching the airways [1,2,3,4].

1 Traumatic Tracheal Injury

The incidence of TI among patients after chest and neck injury can be estimated up to 2%, including those who die immediately after the trauma [5]. The rate of TI increases for neck penetrating injury (4.5%). Neck blunt trauma can be either followed by TI due to tracheal tears, fractures of the larynx and trachea, or even to complete laryngo-tracheal separation following neck hyperextension from sudden deceleration [5]. A combination of both mechanisms is frequently observed when neck hyperextension during a vehicle accident is followed by direct collision of the neck with the steering wheel or the dashboard (“padded dashboard syndrome”) [5]. Another common mechanism of TI can be related to a sudden increase of intra-tracheal pressure against a closed glottis caused by the improper use of the seat belt in car accidents. In other events leading to a similar dynamic, chest compressive trauma may occur when there is a quick increase of the pressure in the airway while the glottis is reflexively closed [6, 7].

2 Iatrogenic Tracheal Injury

Iatrogenic TI can be the consequence of endotracheal intubation, an operative endoscopic procedure or it can also occur during esophageal or thyroid surgery. A specific condition of TI can be observed in the surgical treatment of locally advanced thyroid cancer invading the airways.

TIs occurring during tracheal intubation are rare considering the number of procedures performed for general anesthesia. The real occurrence of this complication might be underestimated considering that some short tears are probably misdiagnosed and undergo spontaneous healing [8].

In the last decade, the estimated incidence of iatrogenic TI following tracheal intubation ranges from 0.05% to 0.37% [9]. Double-lumen tube orotracheal intubation is potentially associated with a higher rate of TI due to a more complex procedure, but the frequency of this event remains low, being estimated under 1% [10]. The mechanisms of tracheobronchial rupture have been largely described. The main causes can be identified in overinflated cuff or excessive pushing of the tube. A direct tear caused by the tube itself remains rare. More often, TIs following intubation are located in the posterior aspect of the trachea in the membranous wall or at the junction between the membranous wall and the cartilage. A tear is more likely to occur after double-lumen intubation in consideration of the tube tips and irregular shape [9, 11]. Inadequate tube size is also considered a prominent cause of TI during the procedure, as reported in some case series and supported by the evidence that a higher rate of female patients with smaller body size compared to men present this rare complication [8]. Other risk factors for a TI are multiple vigorous attempts at intubation, intubation carried out in emergency settings, anesthesiologist’s lack of experience, inappropriate use of stylets, rapid inflation, rupture of the cuff, eccentric inflation of the tracheal cuff, malpositioning of the tube tip, tube repositioning without cuff deflation, repetitive coughing, abrupt head and neck movement, anatomic factors with weakness of the membranous trachea, malacia (mostly elderly women), congenital abnormalities, mediastinal compression with distortion of the trachea, inflammatory lesions of the tracheobronchial tree [11, 12].

TI can be also observed as a consequence of other operative procedures such as percutaneous tracheotomy, rigid bronchoscopy, tracheal or esophageal stent placement, endoscopic tracheal treatments (laser therapy, diathermy), and dilation of tracheal stenoses [2, 13].

Another important group of TI are related to direct tracheobronchial damage during open surgery (e.g., esophagectomy and thyroidectomy), when tumor invasion, compression or inflammatory adhesion affecting the airway are present [14].

3 Clinical Scenario

Undiagnosed patients with TI present subcutaneous emphysema in the postoperative course, which worsens after coughing and can be followed by mediastinal emphysema. Usually, pneumomediastinum is asymptomatic but it can generate complications such as compressive pneumothorax, and large pneumomediastinum can either be observed during mechanical ventilation or occur in the postoperative period or later [8].

3.1 Radiological Investigations

Primary radiological investigations include standard cervical and chest X-ray. Computed tomography (CT) can be used to better evaluate mediastinal emphysema in pneumothorax, mediastinal and neck effusions.

Fiberoptic bronchoscopy can be used to define the TI, by directly visualizing the lesion, possibly showing its exact location and extension (length and depth) and for operative purposes as well [14].

4 Special Clinical Conditions

The airway can be injured by either surgical manipulation or by tumor infiltration.

4.1 Tracheal Injury during Thyroid Surgery

Thyroid surgery is one of the most common procedures worldwide and it is considered a safe operation due to the standardization of surgical approaches, the improvement in operating skills, the application of new technologies, and the required training. Nevertheless, despite the improvements in technique and the fact that patients are increasingly centralized, thyroidectomy is not yet free from the risk of complications and death due to the complexity of the anatomy. In thyroid surgery, the overall incidence of complications is approximately 0–54.4% [15,16,17].

A review of more than 11,000 thyroid surgeries reported the incidence of TI to be 0.06% and the most common location of injury is the posterior lateral cartilage-membranous junction near the ligament of Berry. The injury is believed to be secondary to direct trauma resulting from the use of diathermy to dissect the thyroid off the trachea or to necrosis induced by thermal or ischemic compromise of the submucosal plexus, usually with delayed presentation [18, 19].

TI is usually caused by endoscopic surgery or energy-delivering equipment and it might be difficult to detect during surgery, leading to severe postoperative consequences [20]. Typically, TIs occurring during thyroidectomy are immediately recognized and repaired intraoperatively, with a good outcome and low morbidity. In other, less frequent, cases based on an ischemic lesion, TI occurs subacutely with delayed rupture secondary to tracheal necrosis, which can occur even 30–40 days after surgery [20]. The extent of surgery when performing hemithyroidectomy does not exclude the possibility of this occurrence [21].

When the tracheal laceration is detected, the choice of the best treatment depends on several factors, the most important being the lesion’s longitudinal extent, position and size. Surgery is generally the best option for a definitive cure, but conservative treatment is suggested in small-size lesions or non-operable patients. The absolute contraindications to surgery for an acute iatrogenic trauma are very few. Endoscopy is mandatory and is the pivotal examination to diagnose and assess the lesion. If the lesion is small, the mucosa is healthy and surgery sounds like overtreatment, some authors suggest endoscopic treatment with glues and sealants, although the results are conflicting. This therapeutic option is debated when the tear is large and after initial failure. Surgery aims at restoring the airway wall and is usually performed with interrupted suture with absorbable stitches with or without a pedicle flap to help tissue healing. When the lesion is located in the upper airway, the best approach is cervicotomy, while for the lower trachea a right thoracotomy is best [22]. In selected cases a combined approach with the use of negative pressure wound therapy is an effective treatment option for massive pneumomediastinum and subcutaneous emphysema [23, 24].

4.2 Thyroid Tumors Invading the Airways

Complete invasion of the tracheal wall by a neoplasm accounts for a very limited number of cases but represents a particular condition. Intraluminal invasion from a thyroid tumor usually presents with hoarseness, hemoptysis and different grades of fatigue initially and dyspnea later on. In most cases, the airway invasion is misdiagnosed when a well-differentiated thyroid tumor is assessed. Since the symptoms are late and mild, patients are subjected to surgery and found to have compromised airway during neck exploration.

There is no chance to predict the tumor behavior considering that the biological basis of some differentiated tumors is really indolent, while others show a locally invasive attitude. Prevention of these phenomena is currently impossible, and the diagnosis should take this possible occurrence into account. Despite tracheal infiltration being a severe condition in the context of a thyroid tumor, it is mostly asymptomatic, making its misdiagnosis before thyroidectomy more than likely. When symptoms or neck ultrasound imaging are suggestive for tracheal invasion, bronchoscopy is mandatory. Tracheoscopy represents the gold standard and is very effective for achieving the diagnosis. Moreover, the endoscopic assessment of the airway allows for a fine evaluation of the length, grade, and level of the stenosis. In the case of possible surgery with radical intent, fiberoptic bronchoscopy is to be considered suboptimal whereas rigid bronchoscopy seems to be more appropriate, as well as being useful for mechanical dilation when tumor invasion creates a consistent stenosis of the airway lumen.

Endoscopy is not the only required examination. A CT scan, magnetic resonance imaging and a barium swallow test are integrative and necessary for a definitive evaluation of the condition. CT imaging can identify the depth of invasion into the tracheal wall or lumen invasion along with airway surrounding tissues, tumor position, tumor size and anatomical relationships. When the tumors are bulky and the airway is highly compromised, the work-up must evaluate the esophagus as well. In the case of esophageal infiltration, the prognosis is worse and survival decreases [25].

When airway invasion occurs, the work-up is aimed at selecting the best treatment option. Treatment can have a curative intent or be primarily palliative. When the diagnosed tumor is an undifferentiated thyroid tumor, the treatment is usually palliative since the tumor is highly aggressive and mostly non-resectable at diagnosis while, in the case of well-differentiated thyroid tumors, the treatment is often with curative intent. The importance of a correct and margin-free resection is crucial. Several surgical techniques are reported: tracheal shaving, tracheal window and segmental resection and reconstruction. Shaving off the tumor from the external airway wall is reported in many series and has a strict limitation: it works only when the tumor is closely attached to a non-infiltrated trachea. Tracheal windows are performed with controversial results. When the infiltrated area of the trachea is a single and limited spot in the anterior trachea, the window is successful because the defect is efficiently repaired and covered by the surrounding tissues; however, it is likely to be restored with a permanent tracheal deformation when the window is wide and requires sectioning of more than three rings for more than 1/3 of the airway circumference. Even though some suggestions have been given regarding length, diameter and circumference thresholds for performing or abandoning the surgical technique, surgery must be tailored to each single case and planned with a tailoring approach. Segmental resection and end-to-end anastomosis is probably the best option. This operation can guarantee almost normal restoration of airway continuity, and it is the only possible option for wide and asymmetric infiltration with subglottic compromise. On the other hand, airway resection and reconstruction has more potential complications regarding voice, suture dehiscence and reflux/deglutition compared to tracheal shaving. When a curative intent is scheduled, the best surgical strategy is to perform thyroidectomy en-bloc with airway tract resection and lymph node removal. This happens relatively rarely considering the incidence of local recurrence after thyroidectomy with a necessary second operation to remove the compromised airway tract.

When a thyroid tumor invades the airway, the involved tract is usually from the larynx to the mid-trachea. Invasion of the lower trachea is anecdotal. Thus, the procedure to be performed varies largely according to the tumor characteristics. The surgery can be complex with anatomical adaptation of the airway stumps [26].

Considering the thyroid’s position, the larynx, recurrent nerves, cricoid and the subglottic larynx can be involved by the disease. In this regard, a pure tracheal resection and reconstruction accounts for only a limited number of operations scheduled for this indication. Asymmetric reconstruction of the upper airway with partial or total cricoid or thyroid cartilage with or without sacrifice of a recurrent nerve is a common resection to be planned. These operations are possibly technically demanding with specific expertise required. For this reason, patients with suspected thyroid tumor invading the airway should be referred to dedicated centers with specific experience with this tumor and surgery [27].

In the case of highly aggressive tumors or non-resectable disease, the only possible goal is to guarantee ventilation and avoid asphyxia. In this condition, endoscopic treatment can be suggested with airway lumen dilation with or without stenting. Tracheotomy is the very effective and final option [28].