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MDCT & MRI Pictorial review of Blunt traumatic aortic injury

David Tso, Ferco Berger, Anja Reimann, Chris Davison, Joao Inacio, Ahmed Albuali, Savvas Nicolaou. MDCT & MRI Pictorial review of Blunt traumatic aortic injury. Objectives. Review the pathophysiology of blunt traumatic aortic injury (BTAI)

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MDCT & MRI Pictorial review of Blunt traumatic aortic injury

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  1. David Tso, Ferco Berger, Anja Reimann, Chris Davison, Joao Inacio, Ahmed Albuali, Savvas Nicolaou MDCT & MRI Pictorial review of Blunt traumatic aortic injury

  2. Objectives • Review the pathophysiology of blunt traumatic aortic injury (BTAI) • Describe the Presley Trauma Center CT grading system for aortic injury • Present current MDCT protocols for the assessment of blunt traumatic aortic injury • Describe typical primary and secondary findings on MDCT in blunt traumatic aortic injury • Introduce a low dose ultra high pitch MDCT protocol

  3. Introduction • Blunt traumatic aortic injury (BTAI) has a high mortality rate, immediately lethal in 80-90% of cases • 50% of patients that survive the immediate injury die within 24 hours if not promptly treated • Majority of BTAI occur following motor vehicle collisions secondary to high-speed deceleration • Prompt recognition and treatment of BTAI is crucial for long-term survival • Clinical signs absent in up to 1/3 of patients •  suspect BTAI in any severe deceleration or high-speed impact Steenburg SD, et al. Radiology. 2008 Sep;248(3):748-62. Berger FH, et al. Eur J Radiol. 2010 Apr;74(1):24-39. Epub 2009 Aug 8.

  4. Mechanisms of Injury • 75%–80% of thoracic aortic injuries result from high-speed motor vehicle collisions (MVC) involving rapid deceleration due to head-on or side-impact collisions > 50 km/h • Descending aorta is fixed to chest wall, while heart and great vessels are relatively mobile • Sudden deceleration causes a tear at junction between fixed and mobile portions of the aorta, usually near the isthmus • Injury may also occur to ascending aorta, distal descending thoracic aorta, or abdominal aorta Neschis DG, et al. N Engl J Med. 2008 Oct 16;359(16):1708-16. Steenburg SD, et al. Radiology. 2008 Sep;248(3):748-62. Berger FH, et al. Eur J Radiol. 2010 Apr;74(1):24-39. Epub 2009 Aug 8.

  5. Mechanisms of Injury • Shearing forces may cause tears at the aortic isthmus (site of attachment for ligamentum arteriosum) due to inflexibility of the aorta at this site • Direct compression of sternum (osseous pinch) can compress aortic root and cause retrograde high pressure on the aortic valve • Water-hammer effect • Simultaneous occlusion of aorta and sudden elevation of blood pressure Legome, E. Uptodate, 2010. Neschis DG, et al. N Engl J Med. 2008 Oct 16;359(16):1708-16. Berger FH, et al. Eur J Radiol. 2010 Apr;74(1):24-39. Epub 2009 Aug 8.

  6. Imaging Options Adapted from Legome, E. Uptodate, 2010

  7. Imaging findings on CXR • Mediastinal widening > 8 cm • High Sensitivity (> 80%) • Low specificity (< 50%) • Obscured aortic knob • Abnormal paraspinous stripes • Blood in apex of lung (apical cap sign) • NG tube, trachea, or endotracheal tube deviation to right • CXR usually first imaging done in trauma setting • CXR can be normal or only minimally abnormal • Widening of mediastinum with deviation of trachea (T) to the right • Depression of left main-stem bronchus (LM) • Convexity of aortopulmonary window (arrow) • Left apical cap (*) due to mediastinal hematoma J.E. Fishman, J Thorac Imaging. 2000 Apr;2:97-103. Steenburg SD, et al. Radiology. 2008 Sep;248(3):748-62.

  8. Advances in Imaging • Multi-detector CT (MDCT) has become the imaging modality of choice due to its speed, sensitivity and availability • Improved spatial resolution, better overall image quality, and supplemental post-processing techniques have contributed to success of CT • Sensitivity of MDCT for BTAI > 98% • MDCT has almost completely eliminated the use of aortography and transesophageal echocardiography Demetriades D, et al. J Trauma. 2008 Jun;64(6):1415-8. Mirvis SE, Shanmuganathan K. Eur J Radiol. 2007 Oct;64(1):27-40. Epub 2007 Mar 21.

  9. VGH MDCT Protocol • Scan is triggered at aortic arch followed by an 8 sec delay after a trigger HU of 100 is reached • Saline chaser to tighten bolus and eliminate streak artefacts • Single contrast-enhanced phase sufficient for aortic trauma cases • ECG-gating may reduce pulsation artefacts • Additional radiation exposure • Used for equivocal cases • Breath-hold technique to minimize breathing artefacts • Scanner with improved temporal resolution may reduce this Berger FH, et al. Eur J Radiol. 2010 Apr;74(1):24-39. Epub 2009 Aug 8.

  10. Presley Classification • Proposed CT grading system used to estimate the severity of aortic injuries • Severity based on findings of • Mediastinal hematoma • Pseudoaneurysm • Intimal flaps or thrombus • Peri-aortic hematoma • Can be used as an early guide for management and may help predict clinical outcomes Gavant ML. Radiol Clin North Am. 1999 May;37(3):553-74, vi.

  11. Presley Classification: Grade 1 • Grade 1b: • Normal aorta • mediastinal hematoma, aorta surrounded by fatplane • Grade 1a: • Normal aorta • NO mediastinal hematoma Gavant ML. Radiol Clin North Am. 1999 May;37(3):553-74, vi.

  12. Presley Classification: Grade 2 • Grade 2a: • Psuedoaneurysm, intimal flap or thrombus < 1cm • NO mediastinal hematoma • Grade 2b: • Psuedoaneurysm, intimal flap or thrombus < 1cm • Peri-aortic hematoma Gavant ML. Radiol Clin North Am. 1999 May;37(3):553-74, vi.

  13. Presley Classification: Grade 3 • Grade 3a: • regular pseudoaneurysm > 1 cm with intimal flap or thrombus • peri-aortic hematoma • NOinvolvement ascending aorta, arch or branching vessels • Grade 3b: • regular pseudoaneurysm > 1 cm with intimal flap or thrombus • peri-aortic hematoma • involvement of ascending aorta, arch or branching vessels Gavant ML. Radiol Clin North Am. 1999 May;37(3):553-74, vi.

  14. Presley Classification: Grade 4 • Grade 4: • Irregular, poorly defined • Pseudoaneurysm with intimal flap or thrombus • large peri-aortic hematoma Gavant ML. Radiol Clin North Am. 1999 May;37(3):553-74, vi.

  15. Intimal luminal flap & thrombus • Flaps of torn intima often project into the aortic lumen • Thrombus may form in association with intimal flaps along aorta walls where intima has been torn • Important to recognize thombi as potential source of emboli Mirvis SE, Shanmuganathan K. Eur J Radiol. 2007 Oct;64(1):27-40. Epub 2007 Mar 21.

  16. Presley 2A • Minimal aortic injury, intimal flap / thrombus < 1 cm (blue arrow) • No signs of peri-aortic hematoma • Collapsed lung on this window and level setting mimics hematoma (yellow arrow)

  17. Presley 2B B A • Minimal aortic injury, intimal flap / thrombus < 1 cm (A, blue arrow) • Peri-aortic hematoma (B, blue arrow)

  18. Aortic pseudoaneurysm • Most aortic injuries demonstrate clearly defined aortic pseudoaneurysm on CT • Appears as a rounded bulge from the lumen with irregular margins • Arise from anterior aspect of the proximal descending aorta at the level of the left mainstem bronchus and proximal left pulmonary artery • Injury may include entire circumference of the aorta and may involve the aortic wall several centimetres proximal and distal to the pseudoaneurysm Mirvis SE, Shanmuganathan K. Eur J Radiol. 2007 Oct;64(1):27-40. Epub 2007 Mar 21.

  19. Presley 3A * A B C • Regular pseudoaneurysm> 1 cm (A, blue arrows, Aorta lumen asterisk) • Peri-aortic hematoma (B, blue arrows) seen in a sagittal reformat in C • (blue arrow = pseudoaneurysm)

  20. Periaortic mediastinal hemorrhage • Mediastinal hemorrhage does not arise directly from an aorta tear • Usually stable as long as there is not a complete breach of the wall of a major artery • Majority of aorta injuries are associated with mediastinal hemorrhage • BTAI can occur in absence of periaortic hematoma Mirvis SE, Shanmuganathan K. Eur J Radiol. 2007 Oct;64(1):27-40. Epub 2007 Mar 21.

  21. Presley 3B * * • Pseudoaneurysm of the distal aortic arch (yellow arrow) • Peri-aortic extensive mediastinal hematoma (blue arrows) • Asterisks indicate aortic lumen of the arch

  22. Contrast extravasation • Findings on CT • Extensive mediastinal hematoma • Bulging of the mediastinal pleura • Marked displacement of esophagus and trachea • Patients with finding of contrast extravasation are in imminent danger of exsanguination Mirvis SE, Shanmuganathan K. Eur J Radiol. 2007 Oct;64(1):27-40. Epub 2007 Mar 21.

  23. Presley 4 • Irregular pseudoaneurysm (asterisks) • Active extravasation (blue arrows) • Native aortic lumen is narrowed (yellow arrows) * * A B * * C D

  24. Secondary findings • Pseudoaneurysm, intimal dissection, or intraluminal clot can diminish blood flow into the descending aorta  can mimic a coarctation • Aortic lumen below injury site is atypically smaller in caliber • May observe displacement of NG tube, trachea, or esophagus due to mass effects caused by periaortic mediastinal hematoma Mirvis SE, Shanmuganathan K. Eur J Radiol. 2007 Oct;64(1):27-40. Epub 2007 Mar 21.

  25. Atypical 1 * • Pseudoaneurysm (blue arrows) with pseudo coarctation of the aorta • Narrowed lumen (asterisk) • Tracheal bifurcation and NG tube displaced to the right (yellow arrow)

  26. Atypical 2 • Frank transection of the aortic arch in an elderly lady with extensive atherosclerotic plaques • Extravasation without pseudoaneurysm formation (blue arrow) • Extensive peri-aortic and mediastinal hematoma (yellow arrows) • Left hemothorax (red arrow)

  27. Atypical 3 • 2 levels of aortic injury: • Distal descending aorta (blue arrow) • Proximal abdominal aorta (red arrow) • Vertebral body fracture at level of abdominal aorta injury (yellow arrow)

  28. Anatomic variants mimicking BTAI • Aortic spindle • Fusiform dilation of aorta immediately beyond isthmus • Change in aortic caliber and slight indentation at transition can be mistaken for injury • Ductus diverticulum • Developmental outpouching of aorta usually seen at the anteromedial aorta at site of aortic isthmus • Usually appears as a smooth focal bulge with gentle obtuse angles with the aortic wall • Ductus remnant • Fibrous remnant of ductus arteriosus • Often displays linear calcification • Branch vessel infundibula • May simulate traumatic injuries or pseudoaneurysms • Recognized by anatomic configuration and smooth conical margins and presence of a vessel emanating from apex of the infundibulum Mirvis SE, Shanmuganathan K. Eur J Radiol. 2007 Oct;64(1):27-40. Epub 2007 Mar 21. Berger FH, et al. Eur J Radiol. 2010 Apr;74(1):24-39. Epub 2009 Aug 8.

  29. Aortic spindle with ductus remnant • Contrast-enhanced chest CT • Mild contour irregularity in medial aspect of proximal descending thoracic aorta • Ductus remnant arising anteriorly • No mediastinal hemorrhage Volume-rendered image of thoracic aorta Mild narrowing of the isthmic portion of the aorta with slight post-isthmic dilatation just distal to site of ductus remnant Mirvis SE, et al. Eur J Radiol. 2007 Oct;64(1):27-40. Epub 2007 Mar 21.

  30. Ductus diverticulum • Contrast-enhanced chest CT • Smoothly contoured “bump” arising from anterior proximal descending aorta at level of the carina • Consistent with a ductus bump • No mediastinal hemorrhage. Volume-rendered view Outer contour of the ductus and its close proximity to the left pulmonary artery Mirvis SE, et al. Eur J Radiol. 2007 Oct;64(1):27-40. Epub 2007 Mar 21.

  31. 50 yo male MVC, unbelted driver Out pouching from inferior margin of aortic arch concavity posteriorly 1 cm in length Significant mediastinal hematoma within anterior superior mediastinum Forbes J, et al. Eur J Radiol. 2010 In Press

  32. Ductus diverticulum of aorta • No significant change in appearance of aorta or small out pouching • No progression of mediastinal hematoma seen • Stable nature of this lesion consistent with a ductus diverticulum of the aorta Forbes J, et al. Eur J Radiol. 2010 In Press

  33. BTAI: Role of MRI • Magnetic resonance (MR) angiography has excellent characteristics for detecting BTAI • May be a strategy for radiation dose reduction in young trauma victims • MR in trauma patient limited due to logistical issues • Although not optimal in acute settings, MRI can be a useful in complex cases • Can demonstrate subintimal hemorrhage that can be a clue to traumatic thoracic aortic dissection • Flash thoracic CT – Low dose • Follow up for post stent Forbes J, et al. Eur J Radiol. 2010 In Press Steenburg SD, et al. Radiology. 2008 Sep;248(3):748-62.

  34. MRI follow-up of Stent graft repair CT follow-up after stent graft repair MRI follow-up 1 year after stent graft repair

  35. Imaging follow-up post-repair Focal aneurysm seen is a focal expansion of the stent

  36. High pitch MDCT protocol • Motion artefacts may be misinterpreted as BTAI • Using dual source CT  can achieve high temporal resolution • Maximum pitch = 3.2 • Advantage = ability to capture images of the aorta and other vascular structures with little motion artefact • Can be non-ECG-triggered for ultrafast spiral scanning • Faster post-processing reconstruction times • Bolus injection of 5 cc/sec of optiray 320 for 80cc, followed by 40 cc of saline • Premonitoring is at the Pulmonary artery. • Scan is triggered at 100 HU. FLASH protocol uses 10 sec delay after HU threshold is reached

  37. Screening for BTAI Nzewi O, et al. Eur J Vasc Endovasc Surg. 2006 Jan;31(1):18-27. Epub 2005 Oct 14.

  38. Treatment for BTAI • Open surgical repair previously the mainstay of therapy • Endovascular stenting becoming more common since it is less invasive and has less complications • Aggressive blood pressure control necessary if any delay in surgical treatment • HR < 100 bpm • SBP < 100 mmHg • Do not delay surgery if imaging or clinical findings reveal evidence of active or impending rupture • Contrast extravasation • Pseudocoarctation • Rapid enlargement of a pseudoaneurysm • Large, reaccumulating hemothorax Demetriades D, et al. J Trauma. 2008 Jun;64(6):1415-8. Fabian TC, et al. Ann Surg. 1998 May;227(5):666-76. Steenburg SD, et al. Radiology. 2008 Sep;248(3):748-62.

  39. Future Directions • Need for a more appropriate classification system taking into account a wider spectrum of aortic injuries • Use of ECG-gated MDCT vs. high pitch vs. volume imaging • ECG-gating may reduce pulsation artefacts, but at the cost of additional radiation exposure • High pitch allow faster scanning times, reducing motion artefacts • Increase in number of detectors enabling greater coverage with a single rotation • Dual energy imaging • Utility of virtual non-contrast and bone subtraction in visualizing aorta and related vascular structures • Ability to visualize intramural hematoma

  40. Conclusion • Traumatic aortic injury is time-sensitive injury requiring rapid and accurate diagnosis • Contrast enhanced MDCT is imaging modality of choice when investigating aortic injuries with sensitivity similar to angiography • Normal variations in aortic anatomy may mimic aortic injury and must be assessed in context of the clinical picture • MRI is less established in the emergency setting, but may have a role in distinguishing overlapping aortic pathologies

  41. References • Berger FH, van Lienden KP, Smithuis R, Nicolaou S, van Delden OM. Acute aortic syndrome and blunt traumatic aortic injury: pictorial review of MDCT imaging. Eur J Radiol. 2010 Apr;74(1):24-39. Epub 2009 Aug 8. • Steenburg SD, Ravenel JG, Ikonomidis JS, Schönholz C, Reeves S. Acute traumatic aortic injury: imaging evaluation and management. Radiology. 2008 Sep;248(3):748-62. • Gavant ML. Helical CT grading of traumatic aortic injuries. Impact on clinical guidelines for medical and surgical management. RadiolClin North Am. 1999 May;37(3):553-74, vi. • Mirvis SE, Shanmuganathan K. Diagnosis of blunt traumatic aortic injury 2007: still a nemesis. Eur J Radiol. 2007 Oct;64(1):27-40. Epub 2007 Mar 21. • Neschis DG, Scalea TM, Flinn WR, Griffith BP. Blunt aortic injury. N Engl J Med. 2008 Oct 16;359(16):1708-16. • Nzewi O, Slight RD, Zamvar V. Management of blunt thoracic aortic injury. Eur J VascEndovasc Surg. 2006 Jan;31(1):18-27. Epub 2005 Oct 14. • Fishman JE. Imaging of blunt aortic and great vessel trauma. J Thorac Imaging. 2000 Apr;15(2):97-103. • Forbes J, Yong-Hing CJ, Galea-Soler S, Nicolaou S. Ductus diverticulum: A confusing normal variant in the setting of trauma. Eur J Radiol. 2010 In Press • Fabian TC, Davis KA, Gavant ML, Croce MA, Melton SM, Patton JH Jr, Haan CK, Weiman DS, Pate JW. Prospective study of blunt aortic injury: helical CT is diagnostic and antihypertensive therapy reduces rupture. Ann Surg. 1998 May;227(5):666-76. • Demetriades D, Velmahos GC, Scalea TM, Jurkovich GJ, Karmy-Jones R, Teixeira PG, Hemmila MR, O'Connor JV, McKenney MO, Moore FO, London J, Singh MJ, Spaniolas K, Keel M, Sugrue M, Wahl WL, Hill J, Wall MJ, Moore EE, Lineen E, Margulies D, Malka V, Chan LS. Diagnosis and treatment of blunt thoracic aortic injuries: changing perspectives. J Trauma. 2008 Jun;64(6):1415-8.

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