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S3P2Q11EA1_ClinicsArticle

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									                                                                                                                             251


                                                                            RADIOLOGIC
                                                                                CLINICS
                                                                      OF NORTH AMERICA
                                                                                      Radiol Clin N Am 44 (2006) 251–258



 Nonvascular Mediastinal Trauma
 Juntima Euathrongchit,                           MD,     Nisa Thoongsuwan,                   MD,
 Eric J. Stern, MD*

 &   Tracheobronchial injury                                      &    Thoracic duct injury
     Clinical findings                                                 Clinical and radiologic findings of thoracic
     Radiologic findings of tracheobronchial                             duct injury
       injury                                                     &    Miscellaneous
 &   Esophageal injury                                            &    Summary
     Clinical findings                                            &    References
     Radiologic findings of esophageal
       trauma
 &   Tracheoesophageal fistula
     Clinical and radiologic findings of
       tracheoesophageal fistula



  This article discusses the radiologic and clinical              the intrathoracic trachea. The intrathoracic trachea
features of nonvascular mediastinal trauma, and                   courses in the midline with a slight deviation to the
focuses on the tracheobronchial tree, the esopha-                 right, which is caused by the aortic arch. It bifur-
gus, and the thoracic duct. Blunt chest and pene-                 cates into the left and right main bronchi at the
trating trauma account for most of the causes of                  tracheal carina at approximately the T4 vertebral
such nonvascular injuries, but iatrogenic and inha-               body level [Fig. 1]. Both main bronchi are consid-
lation injuries are other well-known causes. The                  ered mediastinal structures before exiting by way of
injury distribution and clinical manifestations are               each hilum to divide into the major lobar bronchi.
different for each structure. In our combined expe-               Tracheobronchial injury (TBI) is reported to occur
rience at a level 1 trauma center, the overall preva-             in only 1% to 3% of patients who have blunt chest
lence of injury in each organ is low compared with                trauma, and in 2% to 9% of those who suffer pene-
vascular injuries. As such, and given the frequent                trating chest injuries [2,3]. The tracheobronchial
nonspecific nature of clinical signs and symptoms                 tree is protected from injury to some extent by sur-
of nonvascular mediastinal injuries, the diagnosis                rounding structures, including the sternum, both
often is delayed and results in poor treatment out-               lungs, and the great vessels anterolaterally, and the
come [1].                                                         thoracic vertebrae and esophagus, posteriorly. As
                                                                  such, injuries to these surrounding structures are
                                                                  seen in association with TBI. Similarly, given poten-
Tracheobronchial injury
                                                                  tially violent injury mechanisms, TBI is associated
The trachea can be divided arbitrarily at the tho-                with closed head injury, spinal cord injury, facial
racic inlet into two parts: the cervical trachea and              fractures, lung injury, aortic traumatic injury, chest


 Harborview Medical Center, Department of Radiology, University of Washington School of Medicine, Seattle,
 WA, USA
 * Corresponding author. Harborview Medical Center, Department of Radiology, University of Washington
 School of Medicine, Box 359728, Seattle, WA 98104-2499.
 E-mail address: estern@u.washington.edu (E.J. Stern).

 0033-8389/06/$ – see front matter © 2006 Elsevier Inc. All rights reserved.                 doi:10.1016/j.rcl.2005.10.001
 radiologic.theclinics.com
252       Euathrongchit et al



                                                                     rina, resulting in rupture of the trachea and
                                                                     bronchi, especially near the lower tracheal–
                                                                     carinal junction.
                                                                    A single, transverse rupture of the tracheobron-
                                                                  chial tree is seen much more commonly than a
                                                                  longitudinal or complex tear. Iatrogenic tracheal
                                                                  rupture from intubation commonly occurs at the pos-
                                                                  terior membranous wall. Inhalation injury, such as
                                                                  inspired hot gases, steam, or toxic fumes (eg, chlorine
                                                                  gas), can result in severe damage to the tracheal
                                                                  mucosa, starting with edema and followed by necro-
                                                                  sis, ulceration, scar formation, and finally, tracheal
                                                                  stenosis [7].
      Fig. 1. Coronal reconstruction of the chest CT scan
      shows normal course of the trachea deviation to the         Clinical findings
      right from the aortic arch (*) and division into the left   Diagnosis of TBI is delayed in up to two thirds of
      and right main bronchus at the T4 vertebral level.          patients because the airway column is maintained
                                                                  by intact peritracheobronchial tissue [7,8]. Com-
      wall injury, and abdominal injuries in from 40% to          mon symptoms of TBI are nonspecific and in-
      100% of cases. Combined esophageal and tracheal             clude dyspnea, cough, hoarseness, and hemoptysis.
      rupture is seen in approximately 20% of cases of            Clinical signs also are nonspecific and include sub-
      TBI [4].                                                    cutaneous emphysema, hemoptysis, respiratory dis-
         The two primary causes of trauma to the tracheo-         tress, and hypoxia. Persistent pneumomediastinum;
      bronchial tree are penetrating injuries (in ~70% of         pneumothorax; subcutaneous emphysema, despite
      cases) and blunt trauma (in the remainder) [5]. The         treatment; fractures of the first three ribs; or pos-
      other causes of injury, such as foreign body aspira-        terior dislocation of sternoclavicular joint are
      tion, inhalation, and iatrogenic injuries from intu-        suggestive of, or associated with, TBI [10]. Endo/
      bation or tracheostomy, are uncommon.                       bronchoscopy can confirm the diagnosis when the
         Penetrating trauma is seen more commonly in              clinical and radiologic features are suspected. Late
      the cervical, rather than the intrathoracic, trachea        effects of undiagnosed TBI may be tracheobron-
      [2,6,7], and usually involves the anterior portion of       chial stenosis from granulation tissue and fibrosis
      tracheal cartilage and intercartilaginous ligament.         that leads to chronic airway obstruction.
      For the intrathoracic airway, the distal trachea,
      just above the carina, and the right lower bronchus         Radiologic findings of tracheobronchial injury
      are the regions that are involved most com-
                                                                  The most direct radiologic sign of tracheal rupture
      monly [7].
                                                                  is demonstration of a tracheal wall defect or tra-
         In contrast to penetrating injuries, 80% of cases
                                                                  cheal deformity. These findings are seen far more
      of blunt TBI occur within 2.5 cm of the carina
                                                                  readily using CT than conventional radiography. In-
      [7,8]. The right main stem bronchus tends to be
                                                                  direct signs of injury include an airway leak into the
      injured more commonly than the left because there
                                                                  surrounding mediastinal tissue, an abnormal con-
      is less protection from surrounding structures [7,8].
                                                                  figuration of the endotracheal tube balloon cuff,
         Mechanisms of blunt tracheal injury include the
                                                                  and distal lung parenchymal abnormalities (eg, per-
      following [7,9,10]:
                                                                  sistent atelectasis). The most common radiologic
      •    Rapid increased intraluminal tracheal pressure
           from sudden chest compression against a closed
                                                                  features of TBI are pneumomediastinum (60%)
                                                                  and pneumothorax (≤70%) that result from air
           glottis, typically during high-speed crashes. In       escaping through a tracheal tear into the mediasti-
           these cases, rupture usually occurs in the mem-        num and pleural space [11]. Persistent subcuta-
           branous portion.                                       neous emphysema, pneumothorax, or atelectasis,
      •    Separation and stretching of the tracheobron-
           chial tree due to anteroposterior chest compres-
                                                                  despite appropriate therapy, should be considered
                                                                  suspicious for TBI in the proper clinical setting.
           sion and hyperextension of the neck or direct            Deviation of an endotracheal tube from its ex-
           crushing of the trachea between the sternum            pected course, and focal overdistension of the en-
           and thoracic vertebrae, causing tracheobron-           dotracheal tube balloon cuff or protrusion of the
           chial disruption.                                      balloon through a tracheal laceration are highly
      •    Rapid deceleration with shearing forces passed
           to the relative fixed cricoid cartilage and ca-
                                                                  suggestive radiologic findings for tracheal injury
                                                                  [Figs. 2 and 3] [9]. The lung distal to the injury
                                                                             Nonvascular Mediastinal Trauma           253




Fig. 2. Tracheal rupture from a high-speed vehicle accident. (A) The axial CT scan of the cervical spine shows
the focal left posterolateral protrusion of the endotrachial tube balloon cuff (arrow). (B) The sagittal CT scan of
the cervical spine again shows the focal protrusion of the balloon cuff (arrow). (C ). With the three-dimensional
reconstruction, the abnormal figure of the balloon cuff is demonstrated well (arrow).



can be atelectatic, especially with complete disrup-       number of patients who have TBI who are diag-
tion of the airway. The distal collapsed lung will         nosed in the acute trauma setting.
‘‘fall’’ to the most dependent portion of the pleural
space, which produces the so-called ‘‘fallen lung
                                                            Esophageal injury
sign.’’ Although essentially pathognomonic for the
diagnosis of TBI, it is a rare finding [10,11].            The esophagus can be divided into three portions:
   Whereas conventional chest radiograph is the            cervical, thoracic, and intra-abdominal. The intra-
initial imaging study for the evaluation of blunt          thoracic esophagus is located along the right lateral
chest trauma, and typically establishes the diag-          descending aorta in the middle mediastinum, be-
noses of pneumothorax and pneumomediastinum,               hind the trachea and in front of the thoracic spine.
the direct diagnosis of TBI is made more much              Protected by the thoracic cage, the incidence of
confidently and commonly with CT [9]. Multi-               esophageal injury from external chest trauma is
detector CT (MDCT) has improved markedly our               rare, typically less than 1% [4,12,13]. The most
ability to make this diagnosis, particularly when          common cause of esophageal perforation is medi-
supplemented by the use of thin-slice collimation,         cal procedures [14,15], such as endoscopy and
multiplanar reformation, mini–maximum intensity            dilation procedures. Typically, these procedures
projection rendering, and virtual CT bronchoscopy.         are performed for esophageal pathology that results
The increasing use of screening chest CT in patients       in a weaker wall that is more prone to perforation.
who have blunt chest trauma should increase the            The remaining causes of esophageal injury include
254    Euathrongchit et al




      Fig. 3. Tracheal rupture after blunt trauma. (A) Admission chest radiograph of elderly woman shows diffuse soft
      tissue air and huge hiatal hernia. (B) CT shows air surrounding thoracic trachea with apparent bulging of
      endotracheal balloon posteriorly. (C and D). Coronal and sagittal volume rendered images confirm endotracheal
      balloon bulging through membranous tracheal tear (arrow in C).

      certain toxic ingestions, emetic injury (Boerhaave’s     subcutaneous emphysema, pneumomediastinum,
      syndrome), and external penetrating trauma.              pneumothorax, and demonstration of gastric con-
        Penetrating esophageal injuries result mainly from     tents in pleural fluid. Most cases of blunt or pene-
      gun shot, shotgun, and stab wounds [16]. Penetrat-       trating esophageal injury are delayed in diagnosis,
      ing and blunt esophageal ruptures often are asso-        which leads to a poor outcome [4,16].
      ciated with injury to the surrounding organs, such
      as heart, great vessels, trachea, and spine [17].
                                                               Radiologic findings of esophageal trauma
                                                               Patients who have a penetrating injury track
      Clinical findings                                        through the mediastinum should be evaluated by
      Esophageal injuries have a high morbidity and mor-       esophagography, starting with water-soluble con-
      tality, and early diagnosis and treatment improve        trast media, and if negative, followed by barium
      outcome. Symptoms and signs of esophageal in-            swallow; the higher density contrast allows detec-
      jury are dependent on the depth of esophageal            tion of smaller lesions or contrast leaks. Flexible
      wall involvement. The most common symptom of             fiber optic or rigid esophagoscopy also can be per-
      esophageal injury is retrosternal chest pain. Other      formed with a diagnostic sensitivity that ranges
      nonspecific symptoms include dysphagia, odyno-           from 50% to 90% [4].
      phagia, pleuritic chest pain, and dyspnea. Signs of        The depth of esophageal penetration directly
      full-thickness tear without tracheal trauma include      affects radiologic findings. In superficial penetrat-
                                                                           Nonvascular Mediastinal Trauma          255


ing injury, esophagography will not demonstrate           right pleural effusion, whereas injury of the lower
a tear easily; however, if the injury extends to          one third results in a left pleural effusion [18].
the lumen, a full-thickness perforation potentially         The chest radiograph, as the usual initial imaging
produces pneumomediastinum, pneumothorax,                 examination to evaluate suspected esophageal per-
pleural effusion, and leakage of contrast medium          foration, is used to demonstrate air collections in
during a swallowing study. Malposition of a surgi-        the mediastinum and subcutaneous soft tissues
cal appliance (eg, stent) or demonstration of a           [Fig. 4]. For confirmation and localization of
foreign body in or near the course of the esopha-         the site of rupture, contrast study of the esophagus
gus on radiography indicates a potential esopha-          can be performed under fluoroscopy with compli-
geal perforation. Progressive leakage of esophageal       mentary conventional radiographs. CT can readily
fluid content with superimposed inflammation              show a small leak of contrast material from the
and infection gradually alters the mediastinal con-       esophagus that may be difficult to visualize on
tour and produces widening and indistinct bor-            conventional radiography, and can detect a small
ders. The anatomic position of the esophagus in           metallic foreign body from accidental ingestion
the thorax results in preferential injury patterns;       [17]. Other CT abnormalities include extraluminal
injury to the superior two thirds usually results in      air, periesophageal fluid, and esophageal thicken-




Fig. 4. Esophageal rupture from an all-terrain vehicle accident. (A) Chest radiograph shows the right pneumo-
thorax (arrowheads) with the chest tube. The lung contusion at the right lung apex also is noted. (B) CT scan of
the chest shows air leakage around the esophagus (arrows). The right pneumothorax (*) and the right rib frac-
ture (arrowhead) also are demonstrated. (C ) The esophagography confirms the leakage at the esophagogastric
junction (arrow).
256    Euathrongchit et al



                                                              chemia producing focal necrosis of the esophageal
                                                              and tracheal walls and subsequent formation of
                                                              a fistula [21,23].

                                                              Clinical and radiologic findings of
                                                              tracheoesophageal fistula
                                                              The most common site of a tracheoesophageal fis-
                                                              tula is at or just above the carina. Classic symptoms
                                                              and signs are evidence of pneumonia or coughing
                                                              after swallowing that occur in the 3 to 10 days after
                                                              chest trauma [23,24]. Esophagography and CT can
                                                              diagnose and demonstrate the fistula location
                                                              directly. Otherwise, radiologic findings are indi-
                                                              rect, and include pneumonia, gaseous dilatation
                                                              of the esophagus, pneumomediastinum, and sub-
                                                              cutaneous emphysema.

      Fig. 5. Esophageal contrast leak. CT was performed
      after esophagram for penetrating mediastinal injury     Thoracic duct injury
      and shows leak of contrast from the esophagus (ar-      The thoracic duct is a lymphatic drainage system
      row). Pneumomediastinum is observed and the tra-        that arises from the cisterna chyli, passes into the
      chea had a full-thickness injury at surgery. (From
                                                              thoracic cavity by way of the aortic hiatus, and
      Mirvis SE. Diagnostic imaging of thoracic trauma. In:
      Mirvis SE, Shanmuganathan K, editors. Imaging in
                                                              courses to the right side of the spine between the
      trauma and critical care. 2nd edition. Philadelphia:    azygos vein and the aorta. At the carinal level, the
      WB Saunders; 2003. p. 297–367).                         course of the thoracic duct changes to the left—
                                                              just lateral to the left side of the trachea—and is
      ing that can be clues to esophageal perforation [see    directed between the esophagus and the left sub-
      Figs. 4 and 5]. Recently, CT has played an increas-     clavian artery, where it drains into the venous sys-
      ing role in evaluating esophageal injury because it     tem at the junction of the left brachiocephalic and
      has come into general use as a common method to         internal jugular veins. Understanding this course
      evaluate patients who have acute chest pain. CT         helps to locate the points of potential injury,
      techniques include imaging with and without intra-      because the lower third of the duct lies mainly to
      venous contrast medium injection and, when pos-         the right of midline and leads to right-sided chylo-
      sible, distending the esophagus with water and          thorax, as opposed to injury to the upper tho-
      ingestion of effervescent granules [19,20].             racic portion, which causes a left-sided chylothorax
                                                              [25,26]. Bilateral chylothoraces may be seen when
                                                              injury occurs near the carina. Isolated external pene-
                                                              trating and nonpenetrating thoracic duct injuries are
      Tracheoesophageal fistula                               rare and usually occur in association with the vas-
      Acquired tracheoesophageal fistula after chest          cular or tracheoesophageal injury [27].
      trauma is rare, and occurs in just 0.2% of patients       Proposed mechanisms of blunt thoracic duct rup-
      who have blunt chest injury [7,21]. Most cases          ture include shearing of lymphatic channels from
      involve young adult patients. In cases of penetrat-     hyperflexion and extension of the vertebral col-
      ing trauma, injury usually involves the trachea and     umn, and disruption of the chyle-containing lym-
      esophagus [22].                                         phatic system from stretching and tearing motion
         Typically, the mechanism of the blunt traumatic      during acute compression [28].
      tracheoesophageal fistula is a compression of the
      trachea and esophagus between the sternum and           Clinical and radiologic findings of thoracic duct
      the vertebrae, which results in injury to the mem-      injury
      branous portion of the trachea and the anterior         Thoracic duct injury results in a chylothorax or
      esophageal wall. Because most young patients            chylopericardium. Prolonged leakage of lymph may
      have a highly elastic chest wall, concurrent fracture   lead to nutritional deficiencies, respiratory dysfunc-
      of the thoracic cage is infrequent. The most com-       tion, and immunosuppression with a mortality of
      mon traumatic cause of tracheoesophageal fistula        up to 50% [29]. Chylous effusions contain a high
      is long-term use of an endotracheal tube and naso-      triglyceride content—greater than 110 mg/dL—that
      gastric tube, with esophageal and tracheal wall is-     produces a milky appearance [25]. Demonstration
                                                                              Nonvascular Mediastinal Trauma            257


of a chylothorax or chylous fluid from a surgical                cheobronchial injuries: treatment and outcomes.
wound is most likely due to thoracic duct perfora-               Ann Thorac Surg 2001;71:2059–65.
tion [26]. If chylothorax is noted after blunt chest       [9]   Chen JD, Shanmuganathan K, Mirvis SE, et al.
trauma, esophageal injury should be sought care-                 Using CT to diagnose tracheal rupture. AJR Am
fully [4].                                                       J Roentgenol 2001;176:1273–80.
                                                          [10]   Stern EJ. Airway rupture/laceration. In: Stern EJ,
   Lymphangiography is the imaging procedure of
                                                                 Hunter JC, Mann FA, et al, editors. Trauma ra-
choice to diagnose and localize a laceration point.              diology companion, methods, guidelines, and
Abnormal lymphangiography shows leakage of con-                  imaging fundamentals. Philadelphia: Lippincott-
trast from the thoracic duct, a lymphocele, or lym-              Raven; 1997. p. 130–1.
phatic obstruction. An indirect sign of leakage that      [11]   Karmy-Jones R, Avansino J, Stern EJ. CT of blunt
is seen on CT is a low-attenuation (negative Houns-              tracheal rupture. AJR Am J Roentgenol 2003;
filed units) intrathoracic fluid collection [1].                 180:1670.
                                                          [12]   Asensio JA, Berne J, Demetriades D, et al. Pene-
                                                                 trating esophageal injuries: time interval of safety
Miscellaneous                                                    for preoperative evaluation–how long is safe?
                                                                 J Trauma 1997;43:319–24.
The remaining traumatic nonvascular mediastinal           [13]   Wicky S, Wintermark M, Schnyder P, et al. Im-
structural injuries are seen rarely, except as case              aging of blunt chest trauma. Eur Radiol 2000;
reports. Phrenic nerve injury may be seen after                  10:1524–38.
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                                                                 early diagnosis and primary repair. Dis Esopha-
                                                                 gus 2004;17:91–4.
Summary                                                   [15]   Ghahremani GG. Esophageal trauma. Semin Roent-
                                                                 genol 1994;29:387–400.
Although nonvascular mediastinal injuries are             [16]   Asensio JA, Chahwan S, Forno W, et al. Pene-
rare, they are associated with a high morbidity                  trating esophageal injuries: multicenter study
and mortality and always should be considered                    of the American Association for the Surgery of
in the appropriate clinical setting. Although chest              Trauma. J Trauma 2001;50:289–96.
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                                                                 Chest Med 1994;15:137–46.
ment, and should be obtained with a low threshold
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in major blunt trauma or penetrating injury that                 esophagography for the evaluation of suspected
may or definitely involves the mediastinum.                      esophageal perforation or rupture. AJR Am J
                                                                 Roentgenol 2004;182:1177–9.
                                                          [20]   Lee S, Mergo PJ, Ros PR. The leaking esophagus:
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