Mediastinal Trauma

Etiology

While the etiologies of isolated mediastinal injuries are unknown, the most common cause of blunt thoracic trauma in the United States is motor vehicle accidents. Factors associated with mediastinal trauma in motor vehicle accidents include high speeds, not wearing a seatbelt, extensive motor vehicle damage, and the presence of steering wheel deformities. Penetrating thoracic trauma most often occurs from gunshots and stab wounds. Other less common causes of penetrating thoracic injury include impalement by objects as a result of industrial accidents, falls, collisions, blast injuries, and military devices.[2],[3]

Epidemiology

While the incidence of isolated mediastinal trauma is unknown, chest trauma is the third most common type of trauma in the United States after head and extremity trauma. About 25% of traumatic deaths in the United States are related to thoracic injuries. The incidence of penetrating thoracic trauma varies greatly by geographic distribution. In Europe, for example, the incidence of thoracic trauma is estimated as low as 4%; however, in war-ridden regions, up to 95% of military deaths may be from penetrating thoracic trauma. In the United States, thoracic gunshot wounds make up about 10% of major traumas, while stab wounds to the thorax make up about 9.5%. [4],[5]

History and Physical

Care of the patient with mediastinal trauma often begins in the trauma bay. First responders can provide crucial information regarding the mechanism of injury that may help the clinician discern whether a mediastinal injury may exist. Trauma to the anterior chest may raise the suspicion of a possible mediastinal injury. As with all trauma patients, the evaluation must be guided with ATLS principles. The primary survey should be conducted to identify life-threatening injuries immediately. For patients with mediastinal injury, the primary survey should identify the presence of hypovolemic shock from bleeding or obstructive shock from cardiac tamponade. Vital sign changes present in hemorrhagic shock include a narrow pulse pressure, hypotension, and tachycardia. Pericardial tamponade can present with becks triad which includes hypotension, muffled heart sounds, and distended jugular veins. After the primary survey is completed, the secondary survey should be conducted by performing a head-to-toe exam to identify potential injuries.

Evaluation

Laboratory Evaluation

Trauma patients seen in the trauma bay with the appropriate mechanism of injury should receive a standard set of laboratory tests. This may include but is not limited to a comprehensive metabolic panel, complete blood count, coagulation parameters, and lactate level.

Radiographic Evaluation

A chest X-ray and focused assessment with sonography in trauma (FAST) exam are frequently used as adjuncts in the secondary survey.  For patients with mediastinal injury, chest  X-ray may show pneumomediastinum in the presence of esophageal or tracheobronchial injury.  The presence of mediastinal widening on a chest X-ray may indicate hemopericardium or bleeding from the great vessels. The FAST exam can help detect the presence of blood in the pericardium with high sensitivity and specificity. However, the practitioner must be aware of possible false negatives in the patient with concurrent hemothorax where pericardial blood can be emptying into the thoracic cavity. 

In addition to a FAST exam, a formal echocardiogram can be used to detect hemopericardium, tamponade physiology, or cardiac injury.  For patients with blunt cardiac injury, an EKG should be obtained and troponins should be checked. A normal EKG with negative troponins essentially rules out blunt cardiac injury. Patients with a hemodynamic compromise along with an abnormal EKG or troponin should have a formal echocardiogram to evaluate for blunt cardiac injury. [6],[7],[8]

In the hemodynamically stable patient, CT scan can be used to detect traumatic mediastinal injuries. CT scan can provide important information on the traumatically injured patient. For victims of penetrating trauma, it can define the trajectory of the penetrating object, telling the clinician of the mediastinum was traversed. CT scan can also detect esophageal or tracheobronchial injuries from both blunt and penetrating trauma. Oral contrast with the CT scan can opacify the esophagus and help detect esophageal injuries. In addition, IV contrast given with CT scan can help find vascular injuries such as aortic transections. [9],[10].

A double contrast esophagogram can also be a helpful adjunct to rule out an esophageal injury. A water soluble contrast is given orally or via a nasogastric tube that has been pulled back into the proximal esophagus. Films are taken after administration of the contrast, and if no leak is detected, the process is repeated with barium. [11],[12] 

Endoscopic Evaluation

For patients with a significant mechanism, a bronchoscopic and endoscopic evaluation may be warranted. Esophagoscopy can help determine if there is trauma to the esophagus. In addition, bronchoscopy can allow for evaluation of the tracheobronchial tree for injury. [13]

Treatment / Management

Patients who are clinically stable, without evidence of injury after appropriate evaluation, may be discharged. Patients with signs or symptoms of blunt cardiac injury should be admitted to the hospital with continuous hemodynamic monitoring for a minimum of 24 hours. Patients who are unstable in the trauma bay who do not improve with resuscitation or bedside maneuvers such as chest tube placement should be taken expeditiously to surgery to rule out cardiac tamponade and significant hemorrhage. In addition, a severe air leak after chest tube placement may necessitate immediate operative exploration to rule out tracheobronchial disruption. Even in penetrating thoracic trauma, only 15% of patients will require surgery. The following provides an overview of specific mediastinal injuries and their appropriate management.

Aortic Injury

Patients with high energy blunt trauma with rapid decelerations are at significant risk for blunt aortic injury. Blunt aortic injury causes immediate death in about 80% of patients. In the remaining patients, the transection is contained within the adventitia, and the patient survives until hospital admission. Prompt diagnosis and treatment of the aortic transection is paramount, as most patients will progress to aortic rupture within 24 hours.

Patients with aortic injury should initially be treated medically with blood pressure control while other more immediately life-threatening injuries are treated. Medical treatment includes the use of anti-hypertensives with negative inotropy effects. Intravenous esmolol is a rapidly acting beta-blocker with short half-life and is ideal for the treatment of blunt aortic transection. The goal is to maintain a heart rate below 100 beats/minute and systolic blood pressure less than 100 mmHg. A calcium channel blocker such as diltiazem can be used if there is a contraindication to beta-blocker. If beta-blocker alone does not achieve blood pressure goals, then intravenous nitroglycerin or nitroprusside can be added. After the patient’s other injuries have been stabilized, the aortic transection can be managed with open repair via thoracotomy or with endovascular repair. [14](A1)

Cardiac Injury

Cardiac injuries can vary from simple contusion to rupture. Patients with contusion should be managed supportively with resuscitation and inotropes or vasopressors. Rarely, patients can have myocardial infarction as a result of severe blunt chest trauma with coronary artery dissection and thrombosis. The left anterior descending artery appears to be the most commonly involved coronary artery because of its anterior location.

Myocardial rupture can occur with severe blunt trauma or with penetrating injury. Often these patients will not survive to hospital presentation as cardiac tamponade can cause rapid deterioration in the field. A pericardial window can be used in patients with equivocal findings on the trauma bay. In a patient with a chest tube who is suspected of a myocardial violation, one must be aware that a FAST exam or echocardiogram can provide a false negative as pericardial blood can be decompressing into the thoracic cavity. The pericardial window can be helpful in making the diagnosis of myocardial injury in these patients. [15]

A pericardial window is carried out by making a 5 to 8 cm incision over the xiphoid process. The linea alba is incised, and the xiphoid is dissected out and removed. Blunt finger dissection is done in the retrosternal space, and the sternum is retracted upwards. The diaphragmatic aspect of the pericardium is identified and grasped by two clamps. Careful hemostasis is obtained prior to opening the pericardium so as to minimize the risk of false positives. The pericardium is then incised between the two clamps, and the fluid is inspected for blood.

Patients with a positive pericardial window should receive a full sternotomy along with opening the pericardial sac. Care must be taken to not damage the phrenic nerve. Superficial lacerations can be repaired with some digital pressure and topical hemostatics. Myocardial lacerations can be repaired using non-absorbable monofilament suture such as 2-0 polypropylene. Pledgeted horizontal and vertical mattresses sutures should be used on ventricular injuries, taking care not to injure coronary arteries. Running repairs can be used on the atria. A bilateral, clamshell thoracotomy can also be used to gain exposure to the heart.

Esophageal Injury

The approach to an esophageal repair should be guided by the anatomical location of the injury and the severity of the injury. Imaging studies and esophagoscopy can define the anatomical location of the injury and help plan the surgical approach. The American Association for the Surgery of Trauma Organ Injury Score for esophageal injuries can be used to assess the severity of the injury. A summary of the severity score is shown in the table below. [16]

Injuries to the cervical esophagus can be approached with a left neck incision along the medial border of the sternocleidomastoid. The platysma and omohyoid muscle can be divided and the lateral portion of the esophagus exposed. Lateral retraction of the sternocleidomastoid muscle and carotid sheath facilitates this exposure along with medial retraction of the trachea. Injury to the recurrent laryngeal nerve should be avoided, and the retroesophageal space can be opened widely. Injuries that are readily exposed can be repaired in two layers. If the injury cannot be easily exposed, the cervical area can be drained with closed suction drains in the retroesophageal space and near contaminated areas. The confines of the neck make cervical esophageal injuries amenable to treatment by drainage alone. In addition, the proximity of other structures to the esophagus, such as the trachea, make exploration for concomitant injuries mandatory. In cases where bilateral exposure is needed, a transverse incision across the midline can be added. When primary esophageal repair is carried out, buttressing the repair with healthy muscle is preferable, especially if there is a combined repair. A flap between a tracheal and esophageal repair can help prevent fistula formation. A strap muscle or sternocleidomastoid muscle can be used to buttress the repair. [17],[18]

In general, rupture of the thoracic esophagus should be approached via a right-sided thoracotomy anywhere from the 4-8 interspace. The distal esophagus can be exposed via a left-sided thoracotomy in the 7 or 8 interspaces. The abdominal esophagus can be approached via laparotomy incision.  How an esophageal injury is managed operatively depends on the stability of the patient. When carrying out a thoracotomy, a posteriorly based intercostal muscle should be preserved for potential buttress of a primary repair. Primary repair is preferred if contamination is not severe and the patient is hemodynamically stable. After anterior retraction of the lung, the esophageal injury is identified, and the segment of the injured esophagus is mobilized. The full extent of the mucosal injury should be exposed by doing a myotomy proximally and distally to the rupture. Once the mucosal injury has been defined, it can be repaired in two layers. The mucosal layer can be reapproximated with absorbable suture whereas the muscular layer can be repaired with permanent suture. It is preferable to buttress the repair with well-vascularized tissue such as an intercostal flap or some pericardium. For thoracic esophageal injuries, the chest should be thoroughly washed out and widely drained with chest tubes. [18],[19](B2)

For patients undergoing a damage control operation, more expeditious management may be warranted. In addition, patients with delayed presentation or severe contamination may not be amenable to primary repair due to poor tissue quality. Severe injuries (grade IV or V) also may not be conducive to primary repair. Options for managing an esophageal repair in these situations include simply placing a t-tube in the perforated segment and bringing it out of the chest wall. Thorough washout of the thoracic cavity along with wide chest tube drainage should also be done. Another option includes diversion with an end cervical esophagostomy and transection of the esophagus at the gastroesophageal junction. The excluded esophagus can then either be resected if the patient’s clinical status permits or simply be widely drained in a damage control situation. A venting gastrostomy tube must be placed in patients who are undergoing esophageal exclusion. The patient can then undergo transfer to the intensive care unit for resuscitation with delayed reconstruction when stable. Those who are hemodynamically stable at the time of initial surgery may undergo reconstruction with a gastric conduit. An esophageal stent may also play a role in selected patients with isolated esophageal injuries or as an adjunct in patients undergoing repair. [20]

Tracheobronchial Injury

Tracheobronchial injuries are rare, occurring in less than 1% of patients with a blunt thoracic injury.  Most patients with tracheobronchial injuries have multiple traumatic injuries to the lungs and chest wall. The right main stem bronchus is most often involved and generally is injured within 1 to 2 cm of the carina. CT scan and bronchoscopy can help guide the surgical approach taken to these patients. [13],[21](B2)

Proximal tracheal injuries should be approached surgically in the neck with a low collar incision. The incision can be carried down to form a “T,” splitting the manubrium at the second intercostal space to gain better exposure of the middle third of the trachea. For exposure of the lower third of the trachea along with access to the carina and right mainstem bronchus, a right thoracotomy should be performed. The left mainstem bronchus should be approached via left thoracotomy and can be a difficult exposure because of the aorta. [13],[21](B2)

Once the injury is identified and exposed, devitalized tissue can be debrided back to healthy tissue. Absorbable sutures can be used for tension-free primary repair. Circumferential injuries may necessitate segmental resection and end-to-end anastomosis. For anastomosis carried out in the neck, maintaining flexion post-operatively is important to avoid tension on the repair. To help create a tension-free repair, blunt dissection of the anterior avascular pretracheal area may be necessary. For more severe injuries that require more mobilization, an infrahyoid suprahyoid release may be necessary. [13],[21](B2)

Emergency Department Thoracotomy

Emergency department (ED) thoracotomy is a potentially lifesaving maneuver for patients with mediastinal trauma who have sustained or on the verge of cardiac arrest. ED thoracotomy allows for pericardiotomy to decompress pericardial tamponade, temporary repair of myocardial wounds, open cardiac message, and cross-clamping of the aorta to increase perfusion of blood to the heart and brain.

A left anterolateral thoracotomy is carried out in the 4 intercostal space. The left thoracic cavity is inspected for any signs of overt hemorrhage. The pericardial sac can then be examined and opened with careful preservation of the phrenic nerve. Any pericardial tamponade can be relieved and any cardiac injuries repaired as described above. The sternum can be transected transversely, and the incision can be extended into a right anterolateral thoracotomy to improve exposure to the heart and examine the right thoracic cavity. Patients who regain vital signs should be taken expeditiously to surgery for definitive surgical management. [22],[23](B3)

Survival from ED thoracotomy varies greatly depending on the location and mechanism of injury and whether the patient had vital signs upon presentation. Patients with isolated stab wounds can have a survival rate as high as 16.8%, while those with gunshot wounds are 4.3%. Survival of ED thoracotomy from blunt injury is poor at only 1.4%. Patients with thoracic injuries have the highest survival rate from ED thoracotomy at 10.7%. Those with abdominal injuries have a survival rate of 4.5%, while those with multiple injuries have a dismal survival rate of 0.7%. [24],[25].

The appropriate indications for resuscitate thoracotomy continue to be debated. Several practice guidelines have been established by various organizations including the American College of Surgeons Committee on Trauma (ACS-COT),[26] the Western Trauma Association (WTA),[27], and the Eastern Association for the Surgery of Trauma.[28] The Practice management guidelines published by the WTA give the following indications for resuscitative thoracotomy:  (A1)

• Blunt trauma patients with less than 10 minutes of CPR,
• Penetrating torso trauma patients with less than 15 minutes of CPR,
• Patients with penetrating trauma to the neck or extremity with less than 5 minutes of prehospital CPR, and
• Patients in profound refractory shock.  

Patients with penetrating mediastinal trauma have the highest survival rate of patients receiving resuscitative thoracotomy. [29](B2)

Differential Diagnosis

• Aortic rupture

• Cardiac laceration

• Claval injury

• Clavicular fracture

• Commotio Cordis

• Flail chest

• Hemothorax

• Intercostal artery injury

• Oesophageal injury

• Rib fracture

Complications

The complication rate of traumatic mediastinal injuries is difficult to determine as the majority of these injuries occur concurrently with other injuries. Complications that occur in these patients can include bronchial or esophageal stricture. In addition, patients with tracheal or esophageal injury can develop tracheoesophageal fistulas. Patients with mediastinal trauma can develop empyema or ventilator-associated pneumonia. In addition, thoracic duct injury and chylothorax can also occur.