Article, Radiology

What is the clinical significance of chest CT when the chest x-ray result is normal in patients with blunt trauma?

a b s t r a c t

Background: Computed tomography (CT) has been shown to detect more injuries than Plain radiography in patients with blunt trauma, but it is unclear whether these injuries are clinically significant.

Study objectives: This study aimed to determine the proportion of patients with normal Chest x-ray result and injury seen on CT and abnormal initial CXR result and no injury on CT and to characterize the clinical significance of injuries seen on CT as determined by a trauma expert panel.

Methods: Patients with blunt trauma older than 14 years who received emergency department Chest imaging as part of their evaluation at 2 urban level I trauma centers were enrolled. An expert trauma panel a priori classified thoracic injuries and subsequent interventions as major, minor, or no clinical significance.

Results: Of 3639 participants, 2848 (78.3%) had CXR alone and 791 (21.7%) had CXR and chest CT. Of 589 patients who had chest CT after a normal CXR result, 483 (82.0% [95% confidence interval [CI], 78.7-84.9%]) had normal CT results, and 106 (18.0% [95% CI, 15.1%-21.3%]) had CTs diagnosing injuries–primarily rib fractures, pulmonary contusion, and incidental pneumothorax. Twelve patients had injuries classified as clinically major (2.0% [95% CI, 1.2%-3.5%]), 78 were clinically minor (13.2% [95% CI, 10.7%-16.2%]), and 16 were clinically insignificant (2.7% (95% CI, 1.7%-4.4%]). Of 202 patients with CXRs suggesting injury, 177 (87.6% [95% CI, 82.4%-91.5%]) had Chest CTS confirming injury and 25 (12.4% [95% CI, 8.5%-17.6%]) had no injury on CT. Conclusion: Chest CT after a normal CXR result in patients with blunt trauma detects injuries, but most do not lead to changes in patient management.

Introduction

The prevalence of life-threatening injury-related conditions has remained relatively constant, yet the use of computed tomography (CT) for trauma evaluation has increased dramatically in the past 15

? This manuscript has been presented at the American College of Emergency Physicians Annual Symposium in San Francisco on October 15, 2011.

?? Awards: 2011 American College of Emergency Physicians Resident Research Award.

? Conflicts of interest and source of funding: This publication was supported by the

National Center for Research Resources and the National Center for Advancing Translational Sciences, National Institutes of Health, through UCSF-CTSI Grant Number UL1 RR024131. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the NIH.

* Corresponding author. Department of Emergency Medicine, Oregon Health and Sciences University, 3181 SW Sam Jackson Park Dr, MC:CR114, Portland, OR 97239. Tel.: +1 503 494 4430(w), +1 650 353 6669(c); fax: +1 503 494 4997.

E-mail addresses: borykea@gmail.com (B. Kea), ruwangamage@gmail.com (R. Gamarallage), hemavairamuthu@yahoo.com (H. Vairamuthu,), Jonathan.Fortman@emergency.ucsf.edu (J. Fortman), KLunney@fresno.ucsf.edu (K. Lunney), GHendey@fresno.ucsf.edu (G.W. Hendey), Robert.Rodriguez@emergency.ucsf.edu (R.M. Rodriguez).

¹ Current affiliation: Department of Emergency Medicine, Oregon Health and Sciences University, Portland, OR.

years [1]. The desire to detect injuries with a near-zero miss rate and the widespread availability of rapid CT have driven this multifold increase in CT use and led many trauma centers to the adoption of complete head-to-pelvis CT scanning protocols for blunt trauma evaluation. Proponents of this “pan-scan” approach cite high sensitivity for radiologic injury diagnosis in blunt trauma of the head and cervical spine, whereas other investigators have shown that this can be a low-yield practice clinically in terms of actual patient care. Few of the injuries detected by CT change patient management and the clinical significance of these injuries may not warrant the risks and costs associated with CT [1,2]. The clinical benefit of CT for blunt trauma, then, remains uncertain.

At least 3 major problems may be associated with the incremental use of CT in trauma. First, the exposure of potentially harmful ionizing radiation to a disproportionately young patient population may have a true effect on cancer induction risk. Chest CT is among the top 3 types of imaging in terms of this overall risk [3]. Although few physicians recognize the risks of CT-related radiation, recent investigation has determined that it is real and quantifiable [4-7,3]. As many as 2% of cancers in the United States may be attributed to CT radiation, and 29 000 future cancers may result from CT scans performed in the year 2007 alone [4-6,3]. Second, CT

is associated with substantial charges and costs–expenditures for CT imaging exceed $2 billion annually in the United States [6]. Lastly, the additional time and resources required to perform, process, and interpret potentially unnecessary CT scans is associated with increased time in the emergency department (ED), which may contribute to ED overcrowding and high rates of patients Left without being seen [1,8]. In a recent national study of ED trauma visits, Korley et al [1] determined that the mean ED stay was 126 minutes (95% confidence interval [CI], 123-131 minutes) longer when CT or magnetic resonance imaging was used even when controlling for severity of illness and detected injuries. Conversely, the time, cost, and radiation associated with CT scanning may represent a net benefit to patient care if a significant number of clinically important injuries are detected by CT that might have been otherwise missed.

The objective of this study is to determine the added diagnostic use of chest CT performed after chest x-ray in adults presenting to the ED with blunt trauma. Specifically, we sought to determine the following: (1) the proportion of patients with a normal initial CXR result who are subsequently diagnosed as having injuries on CT and

(2) the clinical significance (major, minor, or no clinical significance) of injuries detected on CT, as determined by an expert panel. Determination of the number of significant injuries missed by CXR should help define the value of chest CT in this setting and may establish the need for the development of a decision instrument for selective Chest CT scanning in patients with blunt trauma.

Patients and methods

Study design

We analyzed retrospective data from July 2007 through March 2011. Owing to the retrospective data collection, University of California, San Francisco’s Committee on Human Research determined that the study was exempt from requiring patient consent.

Study setting and population

The study was conducted at 2 urban, level I trauma centers in California, San Francisco General Hospital and Community Regional Medical Center in Fresno. We identified patients from a database of patients enrolled in a study designed to develop a decision instrument for selective CXR imaging in blunt trauma [9,10]. Patients were enrolled with the following criteria:

Age greater than 14 years
Blunt trauma occurring within 24 hours before ED presentation

Received chest imaging (CXR and/or chest CT) in the ED as a part of their evaluation for trauma. chest X-rays were performed before chest CT, if chest CT was performed.

Enrollment of participants took place when research assistants were available–daily from 7 AM to 11 PM. Research assistants collecting data were blind to final radiologic readings, abstraction of medical records, and hypotheses.

Outcome determination

Radiologic outcomes were determined using official radiologic reports by board-certified radiologists. Although radiologists were aware that patients were being evaluated for trauma, they were blind to the occurrence of this study. If patients had 2 CXRs, both readings were considered.

With regard to clinical significance outcomes, we used a method similar to that used by Stiell et al [11]. We convened an expert trauma panel consisting of 6 associate-professor-level or

higher emergency physicians and 4 associate-professor-level or higher trauma surgeons to derive our Radiologic Injury Clinical Significance Scale. We generated an inclusive list of chest injuries paired with management changes and interventions, for example, pneumothorax with chest tube placement. Panel members independently reviewed this list and assigned the following values to each injury/intervention pair: major clinical significance, 2 points; minor clinical significance, 1 point; and no clinical significance, 0 points. Investigator, R.M.R., collated and calculated the means for these injury pairs, rounding to the first decimal place. Mean scores of 1.5 to 2.0, 0.5 to 1.49, and 0 to 0.49 were deemed to represent major, minor, and no clinical significance, respectively (Table 1).

Computed tomography techniques and equipment

At San Francisco General Hospital, blunt trauma chest CT consisted of a CT angiography of the chest, using a GE LightSpeed VCT (64-slice scanner; Chalfont St. Giles, UK) after 2009 and a GE CT Hi-Speed (single-slice scanner) before 2009. At Community Region- al Medical Center Fresno, blunt trauma chest CT included both a noncontrast and contrast CT performed with a GE LightSpeed VSX (64-slice scanner).

Data abstraction

Data were abstracted from medical records in a manner consistent with principles put forth by Gilbert et al [12]. Our standardized data collection instrument included age, sex, mecha- nism of injury, vital signs, intoxication, physical examination findings (chest pain, chest tenderness, visible signs of chest injury, and altered mental status), mortality data, ultrasound data (if available), CXR and chest CT results, interventions, and admission data. Research assistants who had been trained by our Research Assistants Program recorded demographic data, initial vitals, and initial laboratory reports. Physicians completed historical and physical examination elements. Another set of research assistants, who were blind to prior subject data collected, completed data abstraction from both electronic and paper medical records of final radiologic readings, admission, and interventions from progress notes or discharge summaries. The first author at the primary site trained the lead abstractor, who trained subsequent abstractors. When patients had more than 1 chest injury, such as multiple rib fractures (of minor clinical significance) and hemothorax with chest tube placement (major clinical significance), they were classified into the most severe category (major clinical significance in this example).

Conflicting or confusing data were presented to the first and last authors who made final decisions regarding interpretation. Meetings were held periodically with medical record abstractors and by telephone to study coordinators at the secondary site. Chart abstractors’ performance was monitored by periodic abstraction of 10% of medical records by the lead author for consistency between abstractors. All data of patients with abnormal chest CT result was reviewed by 2 physicians, and differences were resolved by consensus.

Data analysis

Databases were created in Microsoft Excel (Microsoft Corp, Seattle, WA). We used Stata Corp, version 9.0, to calculate descriptive statistics using proportions and means with interquartile ratios or 95% CIs, as appropriate.

Table 1

Trauma panel consensus of clinical significance classification of radiologic injuries

Radiologic injury No clinical significance Minor clinical significance Major clinical significance

mediastinal hematoma ? No intervention or observation

(outpatient management)

No surgical intervention but observed for N 24 h ? Evacuation or other surgical intervention

Hemothorax ? No intervention or observation (outpatient management)

No chest tube but observed for N 24 h ? Thoracotomy or chest tube placement

Pneumothorax ? No intervention or observation (outpatient management)

No chest tube but observed for N 24 h ? Chest tube placement

Pericardial hematoma/ effusion

No intervention or observation (outpatient management)
No pericardiocentesis or surgical intervention but observed for N 24 h
Pericardiocentesis or other surgical intervention

Pneumomediastinum without pneumothorax

No observation (outpatient management)
Observed for N24 h ^a

Pulmonary contusion ? No intervention or observation

(outpatient management)

No mechanical ventilation but observed for N 24 h ? Mechanical ventilation for contusion

(not for other, eg, altered mental status)

Pulmonary laceration ? No intervention or observation

(outpatient management)

No surgical intervention but observed for N 24 h ? Surgical intervention

Esophageal injury ^a ? No surgical intervention but observed for N 24 h ? Surgical intervention

Bronchial injury ^a ? No surgical intervention but observed for N 24 h ? Surgical intervention

spinal fractures ? No intervention or observation (outpatient management)

No surgery but received in-hospital pain management (IV medicine, nerve block) and observed for N 24 h
No surgery or inpatient pain management (managed on an outpatient basis) but received TLSO
Surgical stabilization/intervention

Rib fractures ^a ? >=2 fractures: received in-hospital pain management ^a

(IV medicine, epidural/nerve block) or observed for N24 h

- >=2 fractures: no in-hospital pain management or observation (managed on an outpatient basis)

Scapular fracture ? No intervention or observation (outpatient management)

No surgery but received in-hospital pain management (IV medicine, nerve block) and observed for N 24 h
Surgical intervention

sternal fracture ^a ? No surgery but had in-hospital pain management and observed for N 24 h

- No surgical intervention or in-hospital pain management (managed on an outpatient basis)
Surgical intervention

Tracheal injury ^a ? No surgical intervention but observed for N 24 h ? Surgical intervention

Aortic and/or great vessel injury

^a ^a ? Surgical intervention

- No surgery but observed for N24 h

Ruptured diaphragm ^a ^a ? Surgical intervention

Clavicle fracture ? No intervention or observation ^a ^a

(outpatient management)

IV, intravenous, TLSO, thoracic lumbosacral orthosis.

^a The trauma panel deemed that the management of this injury was inappropriate for this category and classified possible management options in another category of clinical significance.

Results

Of 3639 total patients enrolled, 2848 (78.3%) had a CXR alone and 791 (21.7%) received both a CXR and chest CT. Fourteen participants were excluded from the study because of unavailability of medical records. The demographics of the enrolled patients who had both chest CXR and CT are shown in Table 2. Fig. 1 illustrates the final classification of injuries.

Outcome by radiologic injury

Radiologic injuries were defined by final radiologic reports as any of the following injuries in the first column, listed in Table 1. Of the 589 patients who had a chest CT after a normal CXR result, 483 (82.0%

[95% CI, 78.7%-84.9%]) had CTs that were also read as normal and 106 (18.0% [95% CI, 15.1%-21.3%]) had CTs that diagnosed injuries, primarily rib fractures, pulmonary contusions, and incidental pneu- mothorax. In patients with a CXR suggesting injury, most had injuries confirmed by chest CT, including multiple rib fractures, pneumotho- rax, hemothorax, and pulmonary contusion.

Outcome by clinical significance

Table 1 shows the results of our a priori expert panel classification (Radiologic Injury Clinical Significance Scale). Of the 589 patients with a normal CXR result, chest CT led to an injury diagnosis of major clinical significance in 12 (2.0% [95% CI, 1.2%-3.5%]), minor signifi-

cance in 78 (13.2% [95% CI, 10.7%-16.2%]), and clinically insignificant

Table 2

Demographics of patients with CT chest

Table 3

Detailed classification of injuries detected on chest CT when CXR result is normal

Demographics, clinical characteristics, and mechanism of injury	CXR and chest CT	Injury	Missed on CXR	Major clinical significance	Minor clinical significance	No clinical significance
Age (y), mean (IQR)	46.6 (30-60)	Rib fractures	66	0	66	0
Male	518 (65.6)	Sternal fracture	22	0	22	0
Mechanism of blunt trauma		Pulmonary contusion	35	0	19	16
Motor vehicle accident	378 (47.8)	Pneumothorax	28	8	13	7
Fall (not from standing)	118 (14.9)	Spinal fractures	15	2	10	3
Pedestrian struck by motorized moving vehicle	103 (13.0)	Hemothorax	10	3	4	3
Motorcycle accident	73 (9.2)	Mediastinal hematoma	8	0	6	2
Other trauma	46 (5.8)	Scapular fracture	4	0	3	1
Fall from standing	27 (3.4)	Pneumomediastinum	3	0	1	2
Bicycle accident	24 (3.0)	without pneumothorax
Struck by blunt object(s)	12 (1.5)	Aortic and/or great	2	2	0	0
Struck by fists or kicked	14 (1.8)	vessel injury
Unknown	16 (2.0)	Pericardial hematoma/	1	0	1	0
Injury severity score, mean (SD)^a	18.5 (11.2)	effusion

Admitted for N 24 h 574 (72.6)

Pulmonary laceration	0	0	0	0
Esophageal injury	0	0	0	0
Bronchial injury	0	0	0	0
Tracheal injury	0	0	0	0
Ruptured diaphragm	0	0	0	0
Total of missed injuries	194	15	145	34

Values are presented as no. (%), unless otherwise indicated. IQR, interquartile ratio.

^a injury severity scores, when available, were retrospectively abstracted from a trauma database of admitted patients at the primary hospital site.

in 16 (2.7% (95% CI (1.7%-4.4%]) cases. Table 3 lists the injuries undetected on CXR but diagnosed by CT according to clinical significance, and Fig. 2 is a graphical depiction of these injuries.

Of the 202 patients with a CXR suggesting traumatic injury, chest CT confirmed radiologic injury in 177 (87.6% [95% CI, 82.4%- 91.5%]) patients and ruled out radiologic injury in 25 patients (12.4% [95% CI, 8.5%-17.6%]). In the 177 patients with radiologic

A single patient could have multiple injuries.

injury on CXR and CT, Major injury was seen in 63 (31.2% [95% CI, 25.2%-37.9%]), Minor injury in 111 (54.9% [95% CI, 48.1%-61.7%]),

and clinically insignificant injury in 3 (1.5% [95% CI, 0.5%-4.3%]) of cases. The calculated ? was 0.94, indicating extremely high interabstractor agreement.

CXR – Total

n = 3639

CXR – Normal

n = 3383

CXR – Abnormal

n = 256

CT Chest Total for CXR – Normal

n = 589

CT Chest Total for CXR – Abnormal

n = 202

CT Chest – Abnormal

n = 106

(18.0%)

(95% CI:

15.1-21.3%)

CT Chest –

Normal

n = 483

(82.0%)

(95% CI:

78.7-84.9%)

CT Chest – Abnormal

n = 177

(87.6%)

(95% CI:

82.4-91.5%)

CT Chest – Normal

n = 25

(12.4%)

(95% CI:

8.5-17.6%)

Major injuries

n = 12

(2.0%)

(95% CI:

1.2-3.5%)

Minor Injuries

n = 78

(13.2%)

(95% CI:

10.7-16.2%)

No Clinically significant injuries

n = 16

(2.7%)

(95% CI: 1.7-

4.4%)

Major Injuries

n = 63

(31.2%)

(95% CI:

25.2-37.9%)

Minor Injuries

n = 111

(54.9%)

(95% CI:

48.1-61.7%)

No Clinically Significant Injuries

n = 3

(1.5%)

(95% CI: 0.5-

4.3%)

Fig. 1. Total enrolled patients, radiographic studies, results, and patient’s ultimate classification of their highest level of radiologic injury by clinical significance.

200

Major Clinical Significance Minor Clinical Significance No Clinical Significance

175

150

125

Number of Detected Injuries

100

Fig. 2. Plain radiograph missed injuries, classified by clinical significance of observed major, minor injuries, and no clinical significance (n = 194).

Discussion

In this study of adult patients with blunt trauma, we found that 18.1% of patients who were evaluated by both CXR and chest CT were diagnosed as having radiologic injuries detected by CT but missed by CXR. Most injuries detected by CT alone, however, were clinically minor or insignificant, resulting in little or no Change in management. Thus, in the setting of a normal CXR result, chest CT was a relatively low-yield test. In those patients who had CXR suggesting injury, chest CT confirmed injury in most cases, and nearly a third were clinically major injuries. Computed tomo- graphy ruled out injury in approximately 12% of these abnormal CXR cases.

At most institutions, standard blunt trauma imaging protocols begin with plain radiography. Because of the increased availability and rapidity of CT scans, CT imaging has replaced plain x-rays as the first step in some institutions. Advocates of routine CT scanning cite much greater sensitivity of CT for injuries [13,14]. However, several studies of head and cervical CT scanning have shown that this increased sensitivity of injury detection does not necessarily translate to the detection of injuries that require an intervention, and no study has demonstrated improved outcomes with routine CT in blunt trauma [1,2,15]. We similarly found that CT detected more injuries than CXR, but at a cost of many additional negative CT scans in patients with a normal CXR result. The CXR result was abnormal in 63 (84%) of 75 patients with major thoracic injury. The challenge is to develop a rational approach to selective use of chest CT to detect the major injuries missed by CXR while minimizing CT scans in patients without injury.

In smaller studies, other investigators have examined the use of CXR and chest CT in patients with blunt trauma. Barrios et al [15] found that patients with a normal screening CXR result were much less likely to have an abnormal subsequent chest CT result compared with those with initial abnormal CXR result (25% vs 81%). Only 9 of 143 patients with a normal CXR result had a change in management via chest CT imaging. Traub et al [13] also showed that chest CT was diagnostically more sensitive than CXR in patients with blunt trauma but found that only 19% (27/141) of their patients had a subsequent investigation and/or intervention because of the chest CT.

In a resource-constrained system, the costs, time, and radiation risk of chest CT cannot be ignored. The charge for the performance and interpretation of trauma chest CT at our institution is $2875. In the year 2007 alone, more than 70 million chest CTs were performed [16]. Although radiation dosage has not yet been directly correlated to cancer, numerous studies have extrapolated the cancer risks from the aftermaths of the atomic bomb and Chernoble. In CT coronary angiography studies, Einstein et al [17] estimated a lifetime attribut- able risk of cancer in a 20-year-old woman from a single CT scan to be 0.70%, whereas Hurwitz et al [18] estimated a relative risk of 1.4% to 2.6% for breast cancer and 2.4% to 3.8% for Lung cancer in 25-year-old women. The cancer-induced mortality risk has been estimated to be as high as 12.5 deaths per 10 000 CTs [19]. Thus, the risks of cancer must be considered against the added benefit of chest CT.

Limitations

There are no standard accepted definitions of Clinically significant changes in management, and practitioners may disagree with our

expert panel classification. To address this potential disagreement, we have included analyses that reflect a full range of interpretations of clinical significance. Because some of our data were collected retrospectively, the true reasons for certain interventions may have been misinterpreted. For example, a patient may have been admitted and observed for concomitant head injuries, or a patient may have been intubated for altered mental status rather than for their chest injury. Because not all patients had a chest CT, it is not possible to calculate the true sensitivity and specificity of these imaging modalities.

Conclusions

Overall, our findings indicate that if chest imaging is indicated in a patient with blunt trauma, it should begin with a CXR. In patients with an abnormal CXR result, chest CT is a high-yield test and reveals many significant injuries. Those patients who have a normal CXR result present a more difficult decision. Routine chest CT detects additional injuries, but most are minor. A decision instrument that would assist the clinician in selective chest CT use in this group is warranted. Such a guideline might include clinical features and CXR results to separate patients with blunt trauma into high risk for clinical injury (benefit from chest CT) and low risk for clinical injury (no need for CT) groups. Given that there may be substantial interspecialty disagreement as to what injuries are important to detect, consensus expert panels like the one we convened would be crucial to the development of an acceptable guideline [20]. Nevertheless, by determining the subset of patients who are unlikely to have a clinically significant injury, it may be possible to safely reduce CT use in this patient population.

In summary, we found that in patients with blunt trauma, chest CT after a normal CXR result rarely detected a clinically significant injury. Although many injuries were found, most were clinically minor or insignificant, resulting in no change in management. Development of a decision instrument to detect important, occult injuries while minimizing the cost, time, and radiation of CT is warranted.

Acknowledgments

The authors thank Phillip Hong, BA; Gabriel Prager, BS; and Matthew Cuenot, BS, for assistance with data collection and entry.

References

AJEM

What is the clinical significance of chest CT when the chest x-ray result is normal in patients with blunt trauma?

a b s t r a c t

Introduction

Patients and methods