Ann Thorac Surg 1997;64:1480-1482
© 1997 The Society of Thoracic Surgeons
Case Report
CT Reconstruction of an Unusual Chronic Posttraumatic Aneurysm of the Thoracic Aorta
Michael J. Reardon, MD,
Thomas D. Hedrick, MD,
George V. Letsou, MD,
Hazim J. Safi, MD,
Rafael Espada, MD,
John C. Baldwin, MD
Department of Surgery, Baylor College of Medicine, and Department of Radiology, The Methodist Hospital, Houston, Texas
Accepted for publication June 16, 1997.
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Abstract
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Chronic traumatic aneurysm of the thoracic aorta is an unusual occurrence. Previously, arteriography was performed on all patients seen in our institution with this entity to allow confirmation of the diagnosis and anatomic delineation for operation. A case of chronic traumatic aneurysm of the distal descending aorta discovered on a routine chest roentgenogram and evaluated with chest computed tomographic scanning with three-dimensional reconstruction is presented. It is our belief that not all thoracic aneurysms require arteriography, and improved methods of computed tomographic scanning allow adequate diagnosis and anatomic delineation with decreased morbidity and cost.
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Introduction
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The incidence of nonpenetrating blunt trauma to the chest has increased along with the increase in high-speed vehicular accidents. Thoracic aortic transection is the second leading cause of death in fatal automobile accidents, with only closed head injury causing a greater number [1]. Approximately 15% of automobile accident fatalities are associated with thoracic aortic injury [1]. Eighty-five percent of individuals in automobile accidents associated with thoracic aortic injury die before receiving medical care; the remaining 15% go on to variable lengths of survival, with only about 2% surviving longer than 3 months to form chronic aneurysms [2]. We repair all chronic traumatic aneurysms of the thoracic aorta due to the high incidence of eventual symptomatology and death if they are left unrepaired [3, 4]. It has been our policy to perform arteriography on all of these patients to allow confirmation of the diagnosis and assessment of the aneurysm anatomy to allow repair. We recently treated a 69-year-old man found on screening chest roentgenography to have what appeared to be a chronic posttraumatic aneurysm of the distal descending thoracic aorta. Chest computed tomographic (CT) scan with three-dimensional reconstruction was carried out to confirm the diagnosis and fully assess the aneurysm to allow repair. We think that most cases of chronic traumatic aneurysm of the thoracic aorta can be adequately evaluated with this modality, with avoidance of the morbidity and increased cost of arteriography.
A 69-year-old man was admitted to the neurosurgery service of Baylor College of Medicine, The Methodist Hospital, with the diagnosis of reflex sympathetic dystrophy of the right hand. His past history was remarkable for a near-fatal automobile accident in 1983, resulting in multiple right rib fractures and partial amputation of his right hand, which was repaired. An admission chest roentgenogram (Fig 1
) revealed a calcified mass in his left posterior mediastinum, thought to be consistent with a chronic traumatic aneurysm. Careful questioning revealed no symptoms referable to this mass.
Chest CT scan was ordered to confirm the diagnosis of chronic traumatic aneurysm, and three-dimensional reconstruction was used to anatomically delineate the aneurysm (Fig 2). Operative correction consisted of resection and 24-mm Dacron graft interposition replacement via left thoracotomy. Because of the simple nature of the aneurysm and the expected short cross-clamp time as well as a very diminutive left atrial appendage in this patient, atrial femoral bypass, which we routinely use in the descending thoracic or thoracoabdominal aorta, was not used. A simple clamp-and-go technique was executed. The patient was discharged to home without complications on the fifth postoperative day.
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Fig 2. . Three-dimensional chest computed tomographic reconstruction showing false aneurysm of the descending thoracic aorta.
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Comment
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Advances in CT technology, specifically the introduction of spiral CT scanners, have led to the development of CT angiography. Computed tomographic angiography involves the acquisition of CT images in a very short period of time. Typically, 60 CT slices, approximately 5 mm thick, are acquired in one 30-second breath hold, allowing a typical thoracic study to be completed in about 2 minutes. Intravenous contrast material is usually introduced via venous access in the arm or elsewhere using an injector technique. The resulting CT scans have a high contrast enhancement of the vessels and can be reconstructed at intervals as short as 2 or 3 mm to provide high-resolution data sets. These data sets can then be reconstructed into maximum intensity projections, which have an appearance very similar to the standard views of a thoracic or abdominal aortogram. Further manipulation of the data set can produce three-dimensional–like images, which can be rotated and viewed from various perspectives. In the evaluation of large and medium-sized vessels, CT scans obtained in this fashion have been shown to be as accurate as traditional catheter angiography. They provide additional insight into the morphology of aneurysms at approximately one third the cost of catheter angiography. These examinations can be performed more quickly than catheter angiography in a properly organized CT department and avoid the morbidity associated with arterial vessel puncture for arteriography.
The Baylor Department of Surgery at The Methodist Hospital sees approximately 550 thoracic aneurysms per year, of which approximately 325 are in the descending thoracic or thoracoabdominal aorta. Among these aneurysms we have seen a significant number of chronic traumatic aneurysms of the thoracic aorta, starting with our first case of successful repair in 1954, and last tabulated in the 1979 analysis of 50 patients with chronic traumatic aneurysm of the thoracic aorta by McCollum and associates [5]. In this wide experience almost all the cases have occurred in the typical areas of transection, the aortic isthmus just distal to the left subclavian artery and the ascending aorta. Two cases also occurred in the transverse arch, but no cases occurred in the distal descending thoracic aorta. The mechanism of injury is thought to be different for this location. Differential deceleration between the relatively fixed aortic arch and the relatively mobile ascending or proximal descending thoracic aorta is thought to create shear forces leading to transection at the ascending aorta or aortic isthmus regions. Transection of the distal descending thoracic aorta is thought to occur when a vertebral fraction or hyperextension allows stress on the aortic wall opposite to the relatively fixed intercostal arteries. In our patient, the posterior wall of the aorta was intact and the false aneurysm was found to arise directly from the anterior wall of the aorta consistent with this proposed mechanism. Furthermore, there was minimal evidence of atherosclerosis in the uninvolved descending thoracic aorta and no evidence of infection. The association of an uninfected false aneurysm of the anterior wall of the descending thoracic aorta with minimal changes of atherosclerosis in the remaining descending thoracic aorta and the associated history of near-fatal blunt thoracic trauma led to the diagnosis of chronic posttraumatic aneurysm in our patient. In our extensive experience with thoracic aneurysms, this is the only chronic posttraumatic aneurysm we have seen at this location.
We previously used aortography to evaluate all patients with chronic thoracic aneurysm of the thoracic aorta. With improving CT technology we are relying less on aortography, with its attendant morbidity and increased cost. We think that contrast-enhanced spiral CT of the chest with three-dimensional reconstruction allows excellent evaluation of these aneurysms with decreased morbidity and cost and should be considered as a primary diagnostic modality.
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Footnotes
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Address reprint requests to Dr Reardon, 6550 Fannin, Suite 2435, Houston, TX 77030.
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References
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- Smith RS, Chang FC. Traumatic rupture of the aorta: still a lethal injury. Am J Surg 1986;152:660–3.[Medline]
- Parmley LF, Mattingly TW, Manion WC, Jahnke EJ. Nonpenetrating traumatic injury of the aorta. Circulation 1958;17:1086–101.[Abstract/Free Full Text]
- Bennett DE, Cherry JK. The natural history of traumatic aneurysms of the aorta. Surgery 1967;61:516–23.[Medline]
- Finkelmeier BA, Mentzer RM Jr, Kaiser DL, Tegtmeyer CJ, Nolan SP. Chronic traumatic thoracic aneurysm. Influence of operative treatment on natural history: an analysis of reported cases, 1950–1980. J Thorac Cardiovasc Surg 1982;84:257–66.[Abstract]
- McCollum CH, Graham JM, Noon GP, DeBakey ME. Chronic traumatic aneurysms of the thoracic aorta: an analysis of 50 patients. J Trauma 1979;19:248–52.[Medline]
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M. J. Reardon, L. D. Conklin, R. Philo, G. V. Letsou, H. J. Safi, and R. Espada
Reply
Ann. Thorac. Surg.,
December 1, 1999;
68(6):
2390 - 2390.
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Abstract
Introduction
