Chest computed tomography (CT) is becoming an established modality in the evaluation of trauma patients. This article provides an overview of the CT findings in patients who have suffered from acute nonpenetrating injury to the chest.
is Associate Professor of Radiology and Medicine, and
Assistant Dean of Graduate Medical Education in the Department
of Radiology at the University of Wisconsin Hospital and
Clinics, Madison, WI.
is Associate Professor and Vice Chair of Radiology in the
Department of Radiology at Oregon Health Sciences University,
Each year in the United States, more than 300,000 patients are
and 25,000 people die as a direct result of chest trauma.
Blunt, or nonpenetrating injury accounts for 90% of chest trauma
seen in civilian populations, and most injuries are due to motor
vehicle accidents and falls.
After the patient has been stabilized, a chest radiograph is
usually performed as the initial imaging study. Because of the
critical nature of the patient's condition, radiographs are limited
to portable, bedside examinations. Portable anteroposterior chest
radiographs are limited by patient positioning, inconsistent
exposure technique, obscuration of thoracic anatomy secondary to
portions of external monitoring and support devices overlying the
patient, limited exposure capability, expiratory views, and
magnification and distortion of the mediastinum.
Chest computed tomography (CT) is becoming an established
modality in the evaluation of trauma patients. CT scanning is more
accurate and detects significantly more injuries than chest
radiography, obviates the need for aortography in many patients
with aortic injury, and affects patient management in a significant
number of patients.
This paper provides an overview of the CT findings in patients who
have suffered from acute nonpenetrating injury to the chest.
Approximately 8,000 cases of traumatic aortic rupture occur in
the United States each year, and traumatic aortic rupture is
responsible for 15% to 20% of all fatalities associated with motor
Approximately 90% of patients with traumatic aortic rupture die
before emergency treatment can be instituted. Most aortic injuries
involve the descending aorta and occur just distal to the origin of
the left subclavian artery.
Several radiographic signs have been described as indicators of
aortic injury, the most sensitive being widening of the mediastinum
and loss of definition of the aortic arch. However, no single
radiographic sign or combination of radiographic signs demonstrates
sufficient sensitivity to detect all cases of traumatic aortic
rupture on chest radiographs without the performance of a large
number of normal aortograms.
A normal chest radiograph has a high negative predictive value
(98%) but a low positive predictive value for aortic injury.
When aortography is performed because of findings on a chest
radiograph, only 10% to 20% of patients will have an aortic injury.
In the past decade, several studies have found CT to be 92% to
100% sensitive and 62% to 100% specific in detecting aortic injury.
CT findings of aortic injury include: the indirect sign of
hemomediastinum and direct signs such as aortic contour deformity
(figure 1), intimal flap, thrombus or debris protruding into the
aortic lumen, pseudoaneurysm (figure 2), abrupt tapering of the
diameter of the descending aorta compared with the ascending aorta
("pseudocoarctation"), and extravasation of intravenous contrast
material. In one study, if the criteria for a positive CT scan
included only direct signs of aortic injury (and excluded
hemomediastinum), the sensitivity and negative predictive value
remained 100%, whereas the specificity increased to 96% and the
positive predictive value increased to 40%.
None of the patients with isolated anterior hemomediastinum at CT
had evidence of aortic injury at follow-up aortography.
In this same study, at least 638 (80%) of 795 patients would have
been spared aortography by undergoing CT first.
Prior to spiral CT studies, the false-positive rate for CT in
the detection of aortic injury was 0% to 39% and the false-negative
rate was 0.7%.
Potential pitfalls in CT interpretation include hemomediastinum due
to sternal or vertebral body fracture; left pleural effusion with
left lower lobe subsegmental atelectasis "surrounding" the aorta;
intraluminal artifacts; atherosclerotic plaques; prominent ductus
arteriosus; and pseudointimal flaps secondary to volume averaging
of the left brachiocephalic vein as it crosses in front of the
aortic arch, the left superior intercostal vein, and right
bronchial arteries branching off the descending aorta.
In one study, if aortography had been reserved for patients whose
chest CT showed hematoma only in a periaortic location, the
negative rate of aortography would have been reduced from 62% to
CT is useful in detecting other injuries to the chest in
addition to aortic injury, as well as showing alternative causes
for mediastinal widening on chest radiography. The latter include
paramediastinal atelectasis or pleural effusion, residual thymic
mediastinal lipomatosis, tortuous vessels, vascular anomalies,
The best technique for performing CT to detect aortic injury has
yet to be determined. The following protocol has been offered:
helical scanning mode with single breath-hold acquisition (if
patient is able), 5-mm thick collimation (reconstructed every 3 mm)
with a pitch of 1.5 to 2, and 150 mL of intravenous contrast
material administered at a rate of 2 to 3 mL/sec after a delay of
30 to 40 seconds (or per software provided with the CT scanner to
monitor contrast material enhancement; Smart prep, GE Medical
Systems, Milwaukee, WI). Scanning begins at the level of the
diaphragm and progresses cephalad to above the aortic arch. The
remainder of the chest is scanned with 7-mm collimation.
Patients with no direct evidence of aortic injury or
hemomediastinum on CT do not require further evaluation unless
serial chest radiographs show progressive mediastinal widening.
Dyer et al
also recommend no further evaluation if isolated anterior
hemomediastinum is present. Patients with direct signs of aortic
tear either go directly to surgery or confirmatory conventional
aortography, depending upon the preference of the surgeon. Patients
with hemomediastinum adjacent to the aorta in which no cause for
the hematoma is identified should undergo conventional aortography
as should patients with indeterminate or inadequate CT studies.
Pulmonary parenchymal injury
Pulmonary contusion--Pulmonary contusion is defined as traumatic
extravasation of blood and edema fluid into the adjacent
interstitial and air spaces as a result of torn vessels but without
substantial tissue disruption.
Findings on chest radiography vary from irregular, patchy areas of
consolidation to diffuse and extensive homogeneous consolidation.
Extensive bilateral contusion may lead to respiratory failure and
adult respiratory distress syndrome.
Radiographic changes of contusion are evident within 6 hours after
trauma to the chest, and resolve rapidly, typically within 3 to 10
CT findings of contusion consist of nonsegmental areas of
consolidation and ground-glass opacification that predominantly
involve the lung directly deep to the area of trauma, often sparing
1 to 2 mm of subpleural lung parenchyma adjacent to the injured
Pulmonary laceration--A laceration is defined as an abnormal
intraparenchymal collection of air resulting from traumatic
disruption of the lung architecture.
Wagner et al
described 4 types of laceration: Type 1 is an air-filled cavity
with or without an air-fluid level, resulting from sudden
compression of a pliable chest wall wherein the air-containing lung
ruptures. Type 2 is an air-containing cavity in a paravertebral
location, resulting from severe compression of the more pliable
lower chest wall and sudden shifting of the lower lobe across the
vertebral body causing a shearing type of injury. Type 3 is a small
peripheral cavity or peripheral linear radiolucency that is always
close to the chest wall where a rib has been fractured, resulting
from a fractured rib that has punctured the lung. Type 4 is a
result of previously formed, firm pleuropulmonary adhesions causing
the lung to tear when the overlying chest wall is violently moved
inward or fractures, diagnosed only at surgery or autopsy.
The intraparenchymal collections of air described by Wagner are
also termed pneumatoceles (figure 4). When traumatic cavities fill
with blood, a hematoma forms. Radiographically, traumatic
pneumatoceles and hematomas are not usually seen until a few hours
or even several days after trauma, initially obscured by
surrounding contusion. The size, shape, thickness of the wall, and
number of pneumatoceles varies widely from patient to patient.
Unlike simple contusion, which resolves fairly quickly and
completely, a laceration generally takes weeks to months to resolve
and may result in residual scarring. Occasionally, pneumatoceles
can become secondarily infected, resembling formation of a
The incidence of tracheobronchial injury (TBI) was reported as
0.4% to 1.5% in clinical series of major blunt trauma and 2.8% to
5.4% in autopsy series of trauma victims.
Because TBI is uncommon, and there are usually other associated
injuries, it often goes unrecognized. The clinical presentation is
varied, and the initial diagnostic evaluation may be misleading.
There is no initial radiographic evidence of TBI in 10% of
and patients who present with radiographic findings of hemothorax
or pneumothorax may initially respond well to treatment of these
conditions, delaying diagnosis of TBI. Definitive diagnosis usually
requires demonstration of injury bronchoscopically.
Failure to recognize TBI may result in death or allow cicatrization
to occur with airway obstruction occurring days or months after
initial injury (figure 5).
More than 80% of tracheobronchial injuries occur within 2.5 cm
of the carina.
There is equal incidence of rupture of the right and left mainstem
The most common radiographic findings are subcutaneous and
mediastinal air due to air leakage into surrounding tissue planes
with dissection into the neck. If the trachea or the proximal left
main bronchus is torn, the air commonly dissects centrally,
producing mediastinal and cervical air collections without
pneumothorax or hemothorax. Although most patients with TBI will
have an abnormal chest radiograph, occasionally the initial
radiograph can be normal.
Pneumomediastinum occurs in most cases of tracheal rupture and in
20% to 77% of all airway injuries,
but is a nonspecific finding and can occur from alveolar rupture
secondary to blunt trauma, esophageal rupture, or positive pressure
ventilatory support. Pneumothorax occurs in 63% to 87% of
tracheobronchial injuries. A pneumothorax that does not resolve
with functioning tube drainage is the sine qua non of mediastinal
tracheal and major bronchial injury.
However, since up to 79% of pneumothoraces due to TBI will respond
to initial treatment with chest tubes,
complete re-expansion of the lung with chest tube does not exclude
TBI. Furthermore, delayed pneumothorax has been reported as late as
13 days following injury.
Late sequelae of partial rupture of a main bronchus are granulation
tissue formation leading to fibrous stricture, bronchiectasis,
atelectasis, and pulmonary fibrosis.
The "fallen lung" sign where the collapsed lung falls away from
the hilum, is very suggestive, if not pathognomonic, of bronchial
tear (figure 6). In the supine position, the lung falls laterally
and posteriorly, and in the upright position, inferiorly away from
the hilum. This is the reverse of simple pneumothorax unrelated to
TBI, in which the lung collapses toward the hilum. Air surrounding
a sharply angulated bronchus, discontinuity, or bronchial air
column truncation (so called "bronchus cut-off" sign), sometimes
with a smooth rounded termination, are other signs of TBI.
Endotracheal tube balloon diameter may be greater than normal in
tracheal injuries because an increased amount of air is required to
raise the cuff-to-tracheal wall pressure required to seal the
airway. The balloon may herniate through the tracheal tear into the
mediastinum. CT scanning can show communications between the
mediastinum and the airway. Subtle signs of pneumomediastinum by CT
may be the only indication of airway injury.
Rib fractures occur in about half of all patients who have had
major blunt chest trauma.
The fractures are often missed on the anteroposterior chest
radiograph because the lateral portions of the ribs are frequently
involved and the fracture line is not tangential to the x-ray beam.
CT may demonstrate rib fractures not evident on the radiograph as
well as complications such as pneumothorax and hemothorax.
Fractures of the 9th, 10th, or 11th ribs are often associated with
splenic (figure 7), renal, or hepatic injury. Because they are
relatively protected, fractures of the 1st, 2nd, and 3rd ribs
usually imply severe trauma to the chest. Fracture of 5 contiguous
ribs or 3 contiguous segmental rib fractures may result in focal
chest wall instability, in which case paradoxical motion of the
"flail" chest may lead to respiratory failure.
Potentially serious morbidity and even death have been
associated with posterior dislocation of the clavicle at the
The displaced clavicle may impinge on the trachea, esophagus, or
great vessels or major nerves in the superior mediastinum. This
injury is better depicted on CT than radiography.
Fractures of the thoracic spine account for 15% to 30% of all
About 70% to 90% of fractures are visible on radiographs.
CT and MR imaging allow detection of otherwise occult fractures and
assessment of the relationship between the fracture fragments and
the spinal cord. Radiographs do not reliably distinguish unstable
burst fractures from the usually stable, simple, anterior wedge
compression fractures. CT and MR are more helpful in making this
distinction and aid in detecting injuries such as retropulsed
fracture fragments and extradural hematomas (figure 8). Spiral CT
allows rapid thin-section imaging of the spine with high-quality
sagittal and coronal reconstructions.
Usually, sternal fractures are not evident on bedside chest
radiographs, but are almost always visible on CT. CT findings
include direct evidence of fracture with or without significant
displacement of fracture fragments and associated retrosternal
hematoma (figure 9). The presence of a fat plane between the
hematoma and the aorta implies that the hematoma is not aortic in
Scapular fractures are diagnosed on the initial chest radiograph
in only a little more than half of patients.
When scapular fractures are not seen on the initial chest
radiograph, they are visible in retrospect in 72% of cases, not
included on the examination in 19%, and obscured by superimposed
structures or artifacts in 9%.
CT of the chest should demonstrate most scapular fractures (figure
10), especially if utilized in combination with conventional
Pleural manifestations of chest trauma
Hemothorax and pneumothorax are common manifestations of
nonpenetrating trauma. Blood can enter the pleural space from
injury to vessels of the chest wall, diaphragm, lung, or
mediastinum. Pneumothorax can occur as a result of lung punctured
by a fractured rib, pulmonary interstitial emphysema, TBI, and
esophageal rupture. On CT, acute hemorrhage into the pleural space
may be recognized by the increased attenuation of the pleural fluid
(figure 11) or by the presence of a fluid-fluid level. Loculation
tends to occur early in hemothorax. Pneumothorax occurs in 15% to
40% of patients with nonpenetrating chest trauma,
and is more commonly detected on CT than chest radiography
(figures 3, 4, and 6).
Diaphragmatic rupture is diagnosed in 1% to 4% of patients
admitted to the hospital with blunt trauma,
and in about 5% of patients undergoing laparotomy or thoracotomy
The most commonly accepted mechanism postulated for the development
of diaphragmatic rupture during blunt trauma is sudden increase in
intrathoracic or intra-abdominal pressure against a fixed
diaphragm. Although there is a reportedly higher incidence of
left-sided injuries, right-sided injuries are thought to be
If diaphragm rupture is not promptly diagnosed, the patient may
remain asymptomatic or develop incarceration of herniated abdominal
viscera, which can occur at a time remote from the incidence of
Preoperative diagnosis based on radiographic findings ranges
from 4% to 63% of cases.
The radiographic findings include normal, hemothorax, pneumothorax,
loss of visualization of the diaphragm, apparent elevation of the
diaphragm, visualization of herniated viscera into the chest,
cephalad extension of an intragastric tube above the level of the
diaphragm, and contralateral shift of the mediastinum in the
absence of a large pleural effusion or pneumothorax. CT findings
include focal constriction ("collar sign") of herniated stomach or
bowel (figure 12), herniation of other abdominal viscera,
visualization of peritoneal fat, bowel, or viscera lateral to the
lung or diaphragm or posterior to the crus of the hemidiaphragm,
and sharp discontinuity of the diaphragm (figure 13). Diaphragm
injuries can also be suspected when the diaphragm is not visualized
("absent diaphragm" sign). Most ruptures involve the posterolateral
portion of the diaphragm at the junction of its central tendon and
posterior leaves and are therefore well seen on CT.
Although focal discontinuity of the diaphragm is said to be the
most common finding in patients with a diaphragmatic tear, it
should be noted that there is a normal increase in diaphragmatic
defects with age, not related to trauma.
Optimal assessment of diaphragmatic dome rupture is obtained using
spiral CT with multiplanar coronal and sagittal reconstructions.
Individual diagnostic sensitivity for detecting diaphragmatic
rupture on CT is 50% to 100% and specificity is 86% to 100%.
The heart and pericardium are fairly well protected from
nonpenetrating injury, and documented traumatic injury is uncommon.
Cardiac injuries caused by blunt chest trauma include cardiac
contusion, cardiac rupture, pneumopericardium, hemopericardium,
cardiac tamponade, and cardiac valve dysfunction. Rapid
accumulation of blood or air in the pericardial space can cause
cardiac tamponade and severe hemodynamic compromise (figure 14).
Bedside sonographic evaluation of the heart is the study of choice
to detect pericardial fluid quickly and noninvasively. CT is also
very sensitive for detecting pericardial fluid or air and may
indicate pericardial hemorrhage as determined by the high CT
attenuation value of the fluid.
Soft-tissue injuries of the chest wall
CT scanning can easily distinguish chest wall from parenchymal
or mediastinal injury, whereas this differentiation may not be
possible with chest radiography. Soft-tissue hematomas of the chest
wall are readily distinguished from parenchymal injury, and
subcutaneous air will not be confused with pneumothorax on CT. CT
scanning can show a broncho-pleural-cutaneous fistula (figure 15),
which may not be appreciated on the chest radiograph.
Role of CT in nonpenetrating chest trauma
CT is the imaging modality of choice in the assessment of
patients with clinical or radiographic findings suggestive of
aortic injury, thoracic spine fracture, or diaphragmatic tear.
Other injuries that can be diagnosed with CT include TBI,
esophageal tear, lung parenchymal injuries, hemothorax,
pneumothorax, and fractures of ribs, sternum, scapula, and
clavicle. Optimal assessment requires careful attention to
technique, including the use of intravenously administered contrast
material and multiplanar reconstructed images, and an awareness of
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