- Email: [email protected]
Is helical computed tomography effective for diagnosis of blunt aortic injury?
Is Helical Computed Tomography Effective for Diagnosis of Blunt Aortic Injury? BRYAN COLLIER, DO,* K. MICHAEL HUGHES, DO,† KEVIN MISHOK, DO,† GARY KRAMER, MD,* AND AURELIO RODRIGUEZ, MD† Computed tomography has had a questionable role in diagnosing blunt aortic injury (BAI). The objective of this study was to determine the effectiveness of helical computed tomography of the thorax (HCTT) for detection of BAI. Trauma Registry data and medical records were reviewed for 2,854 patients admitted over a 32-month period. A total of 243 patients were identified at risk for BAI. Patients were evaluated for BAI because of chest radiograph, physical examination, or clinical suspicion. Eleven of 2,834 patients sustained BAI. Of 243 patients who sustained blunt torso trauma, 232 patients underwent HCTT. Eleven underwent aortography without HCTT. Sixteen patients had an abnormal HCTT, revealing 9 patients with BAI. No delayed BAI were encountered. HCTT effectively screens for BAI. Aortography can be more specifically applied as a diagnostic study when preceded by HCTT. HCTT should not be used as solitary study for BAI as some injuries identified by HCTT do not represent BAI. (Am J Emerg Med 2002;20:558-561. Copyright 2002, Elsevier Science (USA). All rights reserved.)
Approximately 1% of all blunt trauma patients sustains identifiable chest injuries, some of which can have devastating consequences. One half of all trauma fatalities involve some element of chest injury, with 20% of these fatalities attributed to blunt aortic injury (BAI).1 Half of the deaths from BAI occur at the scene of trauma, and 50% of those who survive to arrive at the hospital die within the first 24 hours of admission. Without treatment, BAI has a mortality that exceeds 90%. However, those with prompt recognition and surgery survive more than 70 % of the time.2 Those patients who do survive BAI suffer a morbidity of 8% to 25%, which includes paraplegia secondary to spinal cord ischemia, often attributed to aortic cross clamping.3 Early detection of BAI should be a priority in the evaluation of chest trauma, the second most common cause of traumarelated death.4 Radiographic evaluation and diagnosis of BAI continues to evolve as new technology becomes available. However, plain chest radiograph remains the initial screening tool for blunt chest trauma and is a fundamental element in the evaluation of any trauma patient. No radiographic finding or combination of findings has been shown to accurately preFrom the *Conemaugh Memorial Medical Center, Johnstown, PA, and †Allegheny General Hospital, Pittsburgh, PA. Presented in abstract form at Poster Session at the Sixtieth Annual Meeting of the American Association for the Surgery of Trauma (AAST), October 12-14, 2000 San Antonio, TX. Manuscript received March 2, 2002, accepted May 12, 2002. Address reprint requests to K. Michael Hughes, DO, FACOS, Division of Trauma Surgery, Allegheny General Hospital, 320 East North Avenue, Pittsburgh, PA 15212. E-mail: [email protected] Key Words: Aorta, blunt aortic injury, computed tomography, helical computed tomography, thoracic angiography, aortography. Copyright 2002, Elsevier Science (USA). All rights reserved. 0735-6757/02/2006-0014$35.00/0 doi:10.1053/ajem.2002.35463 558
dict the presence of BAI with positive predictive values of chest radiographs as low as 4%.5,6 Computed tomography (CT) of the chest began to show potential in the evaluation of chest trauma in the 1980s.7 However, CT was initially not sensitive in the diagnosis of BAI. One of the first multicenter trials (50 institutions) describing the early use of CT scanning to evaluate BAI showed diagnostic results in only 75% of patients and equivocal results in 23%. Unfortunately, these early scans were not consistent in terms of contrast use or helical scanning.3 In the 1990s the availability of high-speed helical computed tomography of the thorax (HCTT) increased the value of CT as a screening tool.8-11 Thoracic aortography, with sensitivities and specificities approaching 99% to 100% has long been regarded as the gold standard against which all other diagnostic modalities are compared.12-14 Although thoracic angiography is more specific for BAI than conventional CT, it carries a higher procedural risk because of its invasive nature, and it is cumbersome in the early diagnostic and resuscitation phase of multiple trauma evaluation. Most patients suspected of having BAI by history, physical examination, and plain chest radiograph findings therefore proceed to angiography without HCTT evaluation. The purpose of this study is to determine the effectiveness of HCTT for detection of BAI using a retrospective review of trauma patient records. MATERIALS AND METHODS There were 2,854 trauma patients admitted over a 32month period to a regional trauma center that were reviewed using the trauma registry database and medical records. A preestablished protocol was used to evaluate patients for BAI, which included HCTT. This study was approved and conducted in compliance with institutional review board requirements. Two hundred forty-three patients sustained blunt torso trauma and were identified with possible blunt chest injury. These 243 patients were considered to be at risk for BAI because of the mechanism of injury, such as fall from a significant height or motor vehicle collision, accounting for significant forceful deceleration. Physical examination evidence of blunt chest trauma, such as abrasions or bruising of the chest wall, was also considered as risk for BAI. Plain radiograph evidence of chest trauma also directed further evaluation for BAI. Specific radiographic injury patterns, such as mediastinal abnormalities or injuries suggestive of high-energy dissipation, directed further diagnostic evaluation. Once identified as at risk for BAI, patients underwent chest evaluation with HCTT and/or thoracic aortography. HCTT was performed by using a GE HiSpeed Scanner (GE Medical Corporation, Milwaukee, WI). The scan technique included 5-mm cuts taken from the top of the aortic arch to
COLLIER ET AL ■ HELICAL CT FOR BLUNT AORTIC INJURY
559
FIGURE 1. Patients evaluated for blunt aortic injury.
the carina and 7-mm cuts taken down to the level of the diaphragm. Scanner pitch was set at 1.0. Contrast injection was delivered at 2 mL/s for a total of 125 mL using Optiray 320 (Mallinckrodt, St. Louis, MO) and GE Smart-prep technique (15-second scan delay after initial injection to peak concentration with monitor scans). Diagnostic scans were obtained when maximum intravascular concentration of contrast medium was reached. Thoracic aortography was accomplished using a femoral artery approach. A 6.0-French pigtail catheter was used to cannulate to the level of the ascending aorta above the aortic valve. At least 2 views were taken at 90° to each other. Optiray 320 intravenous contrast medium (Mallinckrodt, St. Louis, MO) was injected at 30 to 40 mL/s for 2 seconds. Six to 10 frames per second were recorded. Those patients with angiographic studies showing BAI went to the operating room for surgical correction. Patients who by HCTT had evidence of BAI underwent thoracic aortography to confirm or exclude the diagnosis. Patients with BAI by HCTT confirmed with aortography also underwent surgical correction. RESULTS During a 32-month period, 2,854 patients were evaluated at a regional trauma center, and 243 of these patients (8.5%) were identified as at risk for BAI. The patients at risk for BAI were mostly male (72%) occupants of motor vehicles (79%), with a mean age of 44.6 years. The average injury severity score was 24.3. Twenty-two people died (9%), 18 (82%) secondary to central nervous system injuries and 4 (18%) secondary to miscellaneous causes including disseminated intravascular coagulation, myocardial infarction, or unknown causes. Eleven patients (0.36% of total, 4.5% of those at risk) were found to have sustained a BAI. Eleven of 243 patients at risk for BAI underwent thoracic aortography without HCTT. One of these 11 patients (9%) was found to have angiographic abnormalities showing BAI. The 10 remaining patients with normal angiograms underwent care for their other injuries. None of these patients showed symptoms or further radiographic evidence of delayed or missed BAI (Fig 1). Two hundred thirty-two patients underwent HCTT, of which 16 (6.9%) were abnormal and went on to undergo thoracic aortography. Of these 16 patients, 9 (56%) were confirmed by angiography to have BAI. Two hundred sixteen patients had HCTT without evidence of BAI. One diagnosis of BAI was made at autopsy after a normal HCTT (0.43%). This patient died of complications of severe traumatic brain injury and not as a result of his BAI.
Of the 243 patients at risk for BAI, 98 (40%) had some documented positive physical finding including chest wall hematoma, seatbelt contusion, or abrasion. Of these 98 patients, 38 (39%) had an abnormal chest x-ray, with the most common abnormality reported as a widened mediastinum. Eighty-eight of the 98 patients (90%) had CT scans performed, of which 15 (15%) were abnormal. Of the 243 patients at risk for BAI, 145 patients had essentially normal physical examinations in terms of chest injury. Fifty-seven (39%) patients had abnormal chest radiographs, with the most common finding reported as a widened mediastinum. A total of 130 patients (90%) of the 145 patients had a CT scan performed; 16 (12%) were read as abnormal. Eighty-eight patients (36%) had CT scans performed based on mechanism alone or at the trauma surgeon’s discretion. Using aortography and intraoperative confirmation of BAI as definitive endpoints, HCTT was evaluated. There were 9 true positives, 215 true negatives, 7 false positives, and 1 false negative found on autopsy. Sensitivity, specificity, positive and negative predictive values, and accuracy were calculated (Table 1). DISCUSSION In 1557, Andreas Vesalius first described BAI in a patient that died as a result of a fall from a horse. Until the advent of the high-speed motor vehicle era, fewer than 90 cases of BAI were reported, with few patients surviving.7 Advances in patient transport, diagnostic technologies, and surgical technique have resulted in increased survival of patients with this injury. Those patients that arrive to the hospital TABLE 1. Results of Helical Computed Tomography of the Thorax (N ⫽ 232) No. of Patients True-positive (TP) True-negative (TN) False-positive (FP) False-negative (FN) Sensitivity ⫽ TP/(TP ⫹ FN) Specificity ⫽ TN/(TN ⫹ FP) Positive predictive value ⫽ TP/(TP ⫹ FP) Negative predictive value ⫽ TN/(TN ⫹ FN) Accuracy ⫽ (TP ⫹ TN)/all patients
%
232 9 215 7 1 90 97 56 99 97
560
AMERICAN JOURNAL OF EMERGENCY MEDICINE ■ Volume 20, Number 6 ■ October 2002
and undergo prompt resuscitation and thoracic evaluation now have expected survival of 71% to 84%.15 The evaluation of multiple trauma, and specifically chest injury, begins with a physical examination and a plain chest radiograph, according to widely accepted advanced trauma life support (ATLS) guidelines. Although the sensitivity and specificity of plain chest radiograph are low for BAI, a chest radiograph remains a valuable screening tool for chest injuries in general.5,6 Most definitive diagnostic evaluations or BAI, either by angiography or HCTT, follow an abnormal chest radiograph finding.6,16,17 This was true of our cohort of patients. Abnormal chest radiograph findings directed all 11 of the patients that underwent immediate thoracic angiography. It is unlikely that a chest radiograph will be replaced as an initial screening method in the evaluation of blunt chest injury. Since the first description of conventional CT use for diagnosis of BAI in 1983, the technology of CT scanning has improved dramatically.18,19 Before CT scanning with contrast and continuous scanning, diagnostic values were reported at approximately 75%. Helical CT has increased the diagnostic accuracy of BAI, reportedly near 100%.8-11 However, thoracic angiography remains the standard against which other methods of evaluation of the mediastinum are compared, although some investigators argue that only thoracotomy or autopsy can truly reveal all BAI.14 In our patients, all of those with angiographic abnormalities underwent thoracotomy, and BAI was confirmed. No patient with a normal thoracic angiogram revealed clinical or chest radiograph evidence of missed or delayed BAI. All normal angiographic studies therefore are reported as true negatives. The accuracy of thoracic aortography in this group of patients was 100%. However, thoracic angiography is an invasive procedure with associated risks of complications. Thoracic angiography also requires that a patient be, under most circumstances, removed from usual monitoring and making continued resuscitative interventions cumbersome and of limited availability. In addition, without the use of an effective screening method, angiograms are often performed with few positive results. In our sample of patients, when angiography was used without prior HCTT, only 1 abnormal examination was encountered in 11 total angiograms. This is consistent with other studies reporting that only 10% to 20% of thoracic angiograms will show aortic abnormalities when performed after chest radiograph findings or clinical suspicion alone.6 This suggests that numerous cumbersome and invasive angiograms would need to be performed to diagnose a small number of BAI. As a result, HCTT is proposed as an effective noninvasive method to evaluate patients who are at risk for BAI. HCTT is an effective test to visualize BAI. However, many surgeons still feel more confident by using the established standard of angiography to confirm the diagnosis of BAI because of its near 100% accuracy. However, HCTT is more convenient to perform and most seriously injured patients undergo CT of other body regions. All patients in our study who underwent HCTT also had CT evaluations of other body regions. Combining HCTT with other CT studies, such as CT of the head or abdomen, requires no additional steps or delays on the way to further resuscitation efforts in the intensive care unit or surgery. The increased time of HCTT does not significantly affect time to surgery
should a confirmatory thoracic angiogram be required. The minimal amount of additional time spent performing an HCTT provides those patients without BAI more timely definitive treatment for other injuries in the intensive care unit and surgery. Each of the 232 patients who underwent HCTT also required CT at the same time to evaluate the head, abdomen, or pelvis. In addition, patients without BAI were able to avoid the complications of an angiogram, as well as additional time in the radiology department with limited monitoring and compromised ongoing evaluation. The number of positive thoracic aortographies is increased when preceded by HCTT. Without prior screening with HCTT, there was 1 of 11 (9.1%) patients with a positive angiogram for BAI. However, when HCTT preceded angiography, the percentage of positive angiograms for BAI increased to 56.3%. In previous reports, only 10% to 20% of angiograms were positive when only proceeded by abnormal chest radiographs.6,20,21 If patients are triaged with HCTT before angiography, thoracic aortography becomes more effective. Wong et al showed similar findings as our results describing a decreased negative rate for aortography after HCTT screening (27%) versus no CT screening (62%).22 HCTT has also been considered for definitive diagnosis of BAI and not limited to screening. No patients reviewed in this study went directly to surgery from HCTT for BAI. However, since this review, 2 patients at our institution have had HCTT with findings specifically showing traumatic aortic lesions. These patients then proceeded directly to surgery without thoracic angiography. This is not currently a uniformly accepted practice, and literature support is limited at this time.10 However, as CT technology improves and 3-dimensional reconstruction more accurately depicts the aorta, the role of angiography in the diagnosis of BAI may diminish. The HCTT performed in this series of patients used 5-mm and 7-mm sections to evaluate the aorta. CT scans of the chest with small interval sections (eg, 3-mm sections) may improve visualization. A small disruption in the aortic intima was only diagnosed at autopsy in our 1 missed injury. This could perhaps be better visualized with these 3-mm sections.23 Specific CT scan protocols with sensitive technique are required if HCTT alone is to evolve as the definitive imaging method for diagnosis of BAI preceding operative repair. Interobserver performance is another reason that HCTT has not been used as a definitive diagnostic tool for BAI.23 Although our data did not evaluate the different radiologists’ and surgeons’ interpretation of the scans, others have shown that interpretations can vary. Fishman et al24 showed that observers of HCTT disagreed 24% of the time as to the presence or absence of mediastinal hematomas and 20% of the time regarding periaortic hematomas. In addition, 31% of the normal HCTT were read as positive by one or more of the radiologists.24 With a critically ill trauma patient, a nontherapeutic thoracotomy would be detrimental, directed by misinterpretation of a normal HCTT. HCTT is described as having a positive predictive value of 6% to 89%.9,25 The positive predictive value reported in our series of patients is well within this range. Our 56% positive predictive value does not suffice as an entirely reliable diagnostic tool. Until positive predictive values of HCTT approach 90% consistently and repeatedly such as
COLLIER ET AL ■ HELICAL CT FOR BLUNT AORTIC INJURY
described by Mirvis et al,9 HCTT should be used for definitive diagnosis of BAI on a limited basis. However, with consistent negative predictive values such as described in our report of 99%, HCTT should be used as the screening test of choice for BAI. In conclusion, HCTT is an effective screening modality for BAI. Although accuracy is greater with thoracic aortography, HCTT has the ability to exclude BAI and avoid unnecessary and cumbersome thoracic angiograms. However, some mediastinum injuries imaged by HCTT do not represent thoracic aortic injury and the utility of HCTT as a definitive diagnostic modality for BAI may have limitations. The authors wish to acknowledge Stephanie Gonzalez for her assistance in preparation of this manuscript.
REFERENCES 1. Feczko JD, Lynch L, Pless JE, et al: An autopsy case review of 142 non-penetrating (blunt) injuries of the aorta. J Trauma 1992;33: 846-9 2. Parmley LF, Mattingly TW, Manion WC, et al: Non penetrating injury of the aorta. Circulation 1958;17:1086-101 3. Fabian TC, Richardson JD, Croce MA, et al: Prospective study of blunt aortic injury: Multicenter trial of the American Association for the Surgery of Trauma. J Trauma 1997;42:374-80 4. LoCicero J, Mattox KL: Epidemiology of chest trauma. Surg Clin North Am 1989;69:15-9 5. Raptopuolos V, Sheiman RG, Phillips DA, et al: Traumatic aortic tear: screening with chest CT. Radiology 1992;182:667-73 6. Mirvis SE, Bidwell JK, Buddemeyer EU, et al: Value of chest radiography in excluding traumatic aortic rupture. Radiology 1987; 163:487-93 7. Mattox KL, Wall MJ: Historical review of blunt injury to the thoracic aorta. Chest Surg Clin N Am 2000;10:167-82 8. Gavant ML, Menke PG, Fabian TC, et al. Blunt traumatic aortic rupture: detection with helical CT of the chest. Radiology 1995;197: 125-33 9. Mirvis SE, Shanmuganathan K, Buell J, et al: Use of spiral computed tomography for the assessment of blunt trauma patients with potential aortic injury. J Trauma 1998;45:922-30
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10. Demetriades D, Gomez H, Velmahos G, et al: Routine helical computed tomographic evaluation of the mediastinum in high-risk blunt trauma patients. Arch Surg 1998;133:1084-8 11. Wilson D, Voystock J, Sariego J, et al: Role of computed tomography scan in evaluating the widened mediastinum. Am Surg 1994;60:421-3 12. BuckmasterMJ, Kearney PA, Johnson SB, et al: Further experience with transesophageal echocardiography in the evaluation of thoracic aortic injury. J Trauma 1994;37:989-95 13. Sturm JT, Hankins DG, Young G, et al: Thoracic aortography following blunt chest trauma. Am J Emerg Med 1990;8:92-6 14. Greenberg MD, Rosen CL: Evaluation of the patient with blunt chest trauma: An evidence based approach. Emerg Med Clin North Am 1999;17:41-62 15. Smith RS, Chang FC: Traumatic rupture of the aorta: still a lethal injury. Am J Surg 1986;152:660-3 16. Seltzer SE, Dorsi C, Kirshner R, et al: Traumatic aortic rupture: plain radiographic findings. Am J Radiol 1981;137:1011-4 17. Sefczek DM, Sefczek RJ, Deeb ZL: Radiographic signs of acute traumatic rupture of the thoracic aorta. Am J Radiol 1983; 141:1259-62 18. Heiberg E, Wolverson MK, Sundaram M: CT in aortic trauma. Am J Radiol 1983;140:1119-24 19. Rigauts H, Marchal G, Baert AI: Initial experience with volume CT scanning. J Computed Assist Tomogr 1990;14:675-82 20. Marnocha KE, Maglinte DDT: Plain-film criteria for excluding aortic rupture in blunt chest trauma. Am J Radiol 1985;144:19-21 21. Tello R, Munden RF, Hooton S, et al: Value of spiral CT in hemodynamically stable patients following blunt chest trauma. Comput Med Imaging Graph 1998;22:447-52 22. Wong YC, Wang LJ, Lim KU, et al: Periaortic hematoma on helical CT of the chest: A criterion for predicting blunt traumatic aortic rupture. AJR Am J Roentgenol 1998,170:1523-5 23. Van Hise M, Primack S, Israel R, et al: CT in blunt chest trauma: Indications and limitations. Radiographics 1998;18:1071-84 24. Fishman J, Nunez D, Kane A, et al: Direct versus indirect signs of traumatic aortic injury revealed by helical CT: performance characteristics and interobserver agreement. Am J Radiol 1999;172: 1027-31 25. Durham R, Zuckerman D, Wolverson M, et al: Computed tomography as a screening exam in patients with a suspected blunt aortic injury. Ann Surg 1994;5:699-704
Approximately 1% of all blunt trauma patients sustains identifiable chest injuries, some of which can have devastating consequences. One half of all trauma fatalities involve some element of chest injury, with 20% of these fatalities attributed to blunt aortic injury (BAI).1 Half of the deaths from BAI occur at the scene of trauma, and 50% of those who survive to arrive at the hospital die within the first 24 hours of admission. Without treatment, BAI has a mortality that exceeds 90%. However, those with prompt recognition and surgery survive more than 70 % of the time.2 Those patients who do survive BAI suffer a morbidity of 8% to 25%, which includes paraplegia secondary to spinal cord ischemia, often attributed to aortic cross clamping.3 Early detection of BAI should be a priority in the evaluation of chest trauma, the second most common cause of traumarelated death.4 Radiographic evaluation and diagnosis of BAI continues to evolve as new technology becomes available. However, plain chest radiograph remains the initial screening tool for blunt chest trauma and is a fundamental element in the evaluation of any trauma patient. No radiographic finding or combination of findings has been shown to accurately preFrom the *Conemaugh Memorial Medical Center, Johnstown, PA, and †Allegheny General Hospital, Pittsburgh, PA. Presented in abstract form at Poster Session at the Sixtieth Annual Meeting of the American Association for the Surgery of Trauma (AAST), October 12-14, 2000 San Antonio, TX. Manuscript received March 2, 2002, accepted May 12, 2002. Address reprint requests to K. Michael Hughes, DO, FACOS, Division of Trauma Surgery, Allegheny General Hospital, 320 East North Avenue, Pittsburgh, PA 15212. E-mail: [email protected] Key Words: Aorta, blunt aortic injury, computed tomography, helical computed tomography, thoracic angiography, aortography. Copyright 2002, Elsevier Science (USA). All rights reserved. 0735-6757/02/2006-0014$35.00/0 doi:10.1053/ajem.2002.35463 558
dict the presence of BAI with positive predictive values of chest radiographs as low as 4%.5,6 Computed tomography (CT) of the chest began to show potential in the evaluation of chest trauma in the 1980s.7 However, CT was initially not sensitive in the diagnosis of BAI. One of the first multicenter trials (50 institutions) describing the early use of CT scanning to evaluate BAI showed diagnostic results in only 75% of patients and equivocal results in 23%. Unfortunately, these early scans were not consistent in terms of contrast use or helical scanning.3 In the 1990s the availability of high-speed helical computed tomography of the thorax (HCTT) increased the value of CT as a screening tool.8-11 Thoracic aortography, with sensitivities and specificities approaching 99% to 100% has long been regarded as the gold standard against which all other diagnostic modalities are compared.12-14 Although thoracic angiography is more specific for BAI than conventional CT, it carries a higher procedural risk because of its invasive nature, and it is cumbersome in the early diagnostic and resuscitation phase of multiple trauma evaluation. Most patients suspected of having BAI by history, physical examination, and plain chest radiograph findings therefore proceed to angiography without HCTT evaluation. The purpose of this study is to determine the effectiveness of HCTT for detection of BAI using a retrospective review of trauma patient records. MATERIALS AND METHODS There were 2,854 trauma patients admitted over a 32month period to a regional trauma center that were reviewed using the trauma registry database and medical records. A preestablished protocol was used to evaluate patients for BAI, which included HCTT. This study was approved and conducted in compliance with institutional review board requirements. Two hundred forty-three patients sustained blunt torso trauma and were identified with possible blunt chest injury. These 243 patients were considered to be at risk for BAI because of the mechanism of injury, such as fall from a significant height or motor vehicle collision, accounting for significant forceful deceleration. Physical examination evidence of blunt chest trauma, such as abrasions or bruising of the chest wall, was also considered as risk for BAI. Plain radiograph evidence of chest trauma also directed further evaluation for BAI. Specific radiographic injury patterns, such as mediastinal abnormalities or injuries suggestive of high-energy dissipation, directed further diagnostic evaluation. Once identified as at risk for BAI, patients underwent chest evaluation with HCTT and/or thoracic aortography. HCTT was performed by using a GE HiSpeed Scanner (GE Medical Corporation, Milwaukee, WI). The scan technique included 5-mm cuts taken from the top of the aortic arch to
COLLIER ET AL ■ HELICAL CT FOR BLUNT AORTIC INJURY
559
FIGURE 1. Patients evaluated for blunt aortic injury.
the carina and 7-mm cuts taken down to the level of the diaphragm. Scanner pitch was set at 1.0. Contrast injection was delivered at 2 mL/s for a total of 125 mL using Optiray 320 (Mallinckrodt, St. Louis, MO) and GE Smart-prep technique (15-second scan delay after initial injection to peak concentration with monitor scans). Diagnostic scans were obtained when maximum intravascular concentration of contrast medium was reached. Thoracic aortography was accomplished using a femoral artery approach. A 6.0-French pigtail catheter was used to cannulate to the level of the ascending aorta above the aortic valve. At least 2 views were taken at 90° to each other. Optiray 320 intravenous contrast medium (Mallinckrodt, St. Louis, MO) was injected at 30 to 40 mL/s for 2 seconds. Six to 10 frames per second were recorded. Those patients with angiographic studies showing BAI went to the operating room for surgical correction. Patients who by HCTT had evidence of BAI underwent thoracic aortography to confirm or exclude the diagnosis. Patients with BAI by HCTT confirmed with aortography also underwent surgical correction. RESULTS During a 32-month period, 2,854 patients were evaluated at a regional trauma center, and 243 of these patients (8.5%) were identified as at risk for BAI. The patients at risk for BAI were mostly male (72%) occupants of motor vehicles (79%), with a mean age of 44.6 years. The average injury severity score was 24.3. Twenty-two people died (9%), 18 (82%) secondary to central nervous system injuries and 4 (18%) secondary to miscellaneous causes including disseminated intravascular coagulation, myocardial infarction, or unknown causes. Eleven patients (0.36% of total, 4.5% of those at risk) were found to have sustained a BAI. Eleven of 243 patients at risk for BAI underwent thoracic aortography without HCTT. One of these 11 patients (9%) was found to have angiographic abnormalities showing BAI. The 10 remaining patients with normal angiograms underwent care for their other injuries. None of these patients showed symptoms or further radiographic evidence of delayed or missed BAI (Fig 1). Two hundred thirty-two patients underwent HCTT, of which 16 (6.9%) were abnormal and went on to undergo thoracic aortography. Of these 16 patients, 9 (56%) were confirmed by angiography to have BAI. Two hundred sixteen patients had HCTT without evidence of BAI. One diagnosis of BAI was made at autopsy after a normal HCTT (0.43%). This patient died of complications of severe traumatic brain injury and not as a result of his BAI.
Of the 243 patients at risk for BAI, 98 (40%) had some documented positive physical finding including chest wall hematoma, seatbelt contusion, or abrasion. Of these 98 patients, 38 (39%) had an abnormal chest x-ray, with the most common abnormality reported as a widened mediastinum. Eighty-eight of the 98 patients (90%) had CT scans performed, of which 15 (15%) were abnormal. Of the 243 patients at risk for BAI, 145 patients had essentially normal physical examinations in terms of chest injury. Fifty-seven (39%) patients had abnormal chest radiographs, with the most common finding reported as a widened mediastinum. A total of 130 patients (90%) of the 145 patients had a CT scan performed; 16 (12%) were read as abnormal. Eighty-eight patients (36%) had CT scans performed based on mechanism alone or at the trauma surgeon’s discretion. Using aortography and intraoperative confirmation of BAI as definitive endpoints, HCTT was evaluated. There were 9 true positives, 215 true negatives, 7 false positives, and 1 false negative found on autopsy. Sensitivity, specificity, positive and negative predictive values, and accuracy were calculated (Table 1). DISCUSSION In 1557, Andreas Vesalius first described BAI in a patient that died as a result of a fall from a horse. Until the advent of the high-speed motor vehicle era, fewer than 90 cases of BAI were reported, with few patients surviving.7 Advances in patient transport, diagnostic technologies, and surgical technique have resulted in increased survival of patients with this injury. Those patients that arrive to the hospital TABLE 1. Results of Helical Computed Tomography of the Thorax (N ⫽ 232) No. of Patients True-positive (TP) True-negative (TN) False-positive (FP) False-negative (FN) Sensitivity ⫽ TP/(TP ⫹ FN) Specificity ⫽ TN/(TN ⫹ FP) Positive predictive value ⫽ TP/(TP ⫹ FP) Negative predictive value ⫽ TN/(TN ⫹ FN) Accuracy ⫽ (TP ⫹ TN)/all patients
%
232 9 215 7 1 90 97 56 99 97
560
AMERICAN JOURNAL OF EMERGENCY MEDICINE ■ Volume 20, Number 6 ■ October 2002
and undergo prompt resuscitation and thoracic evaluation now have expected survival of 71% to 84%.15 The evaluation of multiple trauma, and specifically chest injury, begins with a physical examination and a plain chest radiograph, according to widely accepted advanced trauma life support (ATLS) guidelines. Although the sensitivity and specificity of plain chest radiograph are low for BAI, a chest radiograph remains a valuable screening tool for chest injuries in general.5,6 Most definitive diagnostic evaluations or BAI, either by angiography or HCTT, follow an abnormal chest radiograph finding.6,16,17 This was true of our cohort of patients. Abnormal chest radiograph findings directed all 11 of the patients that underwent immediate thoracic angiography. It is unlikely that a chest radiograph will be replaced as an initial screening method in the evaluation of blunt chest injury. Since the first description of conventional CT use for diagnosis of BAI in 1983, the technology of CT scanning has improved dramatically.18,19 Before CT scanning with contrast and continuous scanning, diagnostic values were reported at approximately 75%. Helical CT has increased the diagnostic accuracy of BAI, reportedly near 100%.8-11 However, thoracic angiography remains the standard against which other methods of evaluation of the mediastinum are compared, although some investigators argue that only thoracotomy or autopsy can truly reveal all BAI.14 In our patients, all of those with angiographic abnormalities underwent thoracotomy, and BAI was confirmed. No patient with a normal thoracic angiogram revealed clinical or chest radiograph evidence of missed or delayed BAI. All normal angiographic studies therefore are reported as true negatives. The accuracy of thoracic aortography in this group of patients was 100%. However, thoracic angiography is an invasive procedure with associated risks of complications. Thoracic angiography also requires that a patient be, under most circumstances, removed from usual monitoring and making continued resuscitative interventions cumbersome and of limited availability. In addition, without the use of an effective screening method, angiograms are often performed with few positive results. In our sample of patients, when angiography was used without prior HCTT, only 1 abnormal examination was encountered in 11 total angiograms. This is consistent with other studies reporting that only 10% to 20% of thoracic angiograms will show aortic abnormalities when performed after chest radiograph findings or clinical suspicion alone.6 This suggests that numerous cumbersome and invasive angiograms would need to be performed to diagnose a small number of BAI. As a result, HCTT is proposed as an effective noninvasive method to evaluate patients who are at risk for BAI. HCTT is an effective test to visualize BAI. However, many surgeons still feel more confident by using the established standard of angiography to confirm the diagnosis of BAI because of its near 100% accuracy. However, HCTT is more convenient to perform and most seriously injured patients undergo CT of other body regions. All patients in our study who underwent HCTT also had CT evaluations of other body regions. Combining HCTT with other CT studies, such as CT of the head or abdomen, requires no additional steps or delays on the way to further resuscitation efforts in the intensive care unit or surgery. The increased time of HCTT does not significantly affect time to surgery
should a confirmatory thoracic angiogram be required. The minimal amount of additional time spent performing an HCTT provides those patients without BAI more timely definitive treatment for other injuries in the intensive care unit and surgery. Each of the 232 patients who underwent HCTT also required CT at the same time to evaluate the head, abdomen, or pelvis. In addition, patients without BAI were able to avoid the complications of an angiogram, as well as additional time in the radiology department with limited monitoring and compromised ongoing evaluation. The number of positive thoracic aortographies is increased when preceded by HCTT. Without prior screening with HCTT, there was 1 of 11 (9.1%) patients with a positive angiogram for BAI. However, when HCTT preceded angiography, the percentage of positive angiograms for BAI increased to 56.3%. In previous reports, only 10% to 20% of angiograms were positive when only proceeded by abnormal chest radiographs.6,20,21 If patients are triaged with HCTT before angiography, thoracic aortography becomes more effective. Wong et al showed similar findings as our results describing a decreased negative rate for aortography after HCTT screening (27%) versus no CT screening (62%).22 HCTT has also been considered for definitive diagnosis of BAI and not limited to screening. No patients reviewed in this study went directly to surgery from HCTT for BAI. However, since this review, 2 patients at our institution have had HCTT with findings specifically showing traumatic aortic lesions. These patients then proceeded directly to surgery without thoracic angiography. This is not currently a uniformly accepted practice, and literature support is limited at this time.10 However, as CT technology improves and 3-dimensional reconstruction more accurately depicts the aorta, the role of angiography in the diagnosis of BAI may diminish. The HCTT performed in this series of patients used 5-mm and 7-mm sections to evaluate the aorta. CT scans of the chest with small interval sections (eg, 3-mm sections) may improve visualization. A small disruption in the aortic intima was only diagnosed at autopsy in our 1 missed injury. This could perhaps be better visualized with these 3-mm sections.23 Specific CT scan protocols with sensitive technique are required if HCTT alone is to evolve as the definitive imaging method for diagnosis of BAI preceding operative repair. Interobserver performance is another reason that HCTT has not been used as a definitive diagnostic tool for BAI.23 Although our data did not evaluate the different radiologists’ and surgeons’ interpretation of the scans, others have shown that interpretations can vary. Fishman et al24 showed that observers of HCTT disagreed 24% of the time as to the presence or absence of mediastinal hematomas and 20% of the time regarding periaortic hematomas. In addition, 31% of the normal HCTT were read as positive by one or more of the radiologists.24 With a critically ill trauma patient, a nontherapeutic thoracotomy would be detrimental, directed by misinterpretation of a normal HCTT. HCTT is described as having a positive predictive value of 6% to 89%.9,25 The positive predictive value reported in our series of patients is well within this range. Our 56% positive predictive value does not suffice as an entirely reliable diagnostic tool. Until positive predictive values of HCTT approach 90% consistently and repeatedly such as
COLLIER ET AL ■ HELICAL CT FOR BLUNT AORTIC INJURY
described by Mirvis et al,9 HCTT should be used for definitive diagnosis of BAI on a limited basis. However, with consistent negative predictive values such as described in our report of 99%, HCTT should be used as the screening test of choice for BAI. In conclusion, HCTT is an effective screening modality for BAI. Although accuracy is greater with thoracic aortography, HCTT has the ability to exclude BAI and avoid unnecessary and cumbersome thoracic angiograms. However, some mediastinum injuries imaged by HCTT do not represent thoracic aortic injury and the utility of HCTT as a definitive diagnostic modality for BAI may have limitations. The authors wish to acknowledge Stephanie Gonzalez for her assistance in preparation of this manuscript.
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