mdct and mri pictorial review of blunt traumatic aortic injury

MDCT & MRI PICTORIAL REVIEW OF BLUNT TRAUMATIC AORTIC INJURYDavid Tso, Ferco Berger, Anja Reimann, Chris Davison, Joao Inacio, Ahmed Albuali, Savvas Nicolaou

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

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

Berger FH, et al. Eur J Radiol. 2010 Apr;74(1):24-39. Epub 2009 Aug 8.

Steenburg SD, et al. Radiology. 2008 Sep;248(3):748-62.

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


Steenburg SD, et al. Radiology. 2008 Sep;248(3):748-62.Neschis DG, et al. N Engl J Med. 2008 Oct 16;359(16):1708-16.

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 pressureBerger FH, et al. Eur J Radiol. 2010 Apr;74(1):24-39. Epub 2009 Aug 8.

Neschis DG, et al. N Engl J Med. 2008 Oct 16;359(16):1708-16.Legome, E. Uptodate, 2010.

Imaging OptionsImaging Modality

Comments

Plain radiograph •Upright preferable; sensitivity of supine unclear•Normal PA radiograph has high negative predictive value; good test for low to moderate suspicion•If high clinical suspicion, or abnormal radiograph, further testing required

Chest CT Scan •Test of choice•Highly sensitive and specific•Requires IV contrast•Can usually proceed directly to OR with positive CT•Equivocal study necessitates angiography

Angiography •Highly sensitive and specific•No longer plays a role, not even when CT results are equivocal•Rarely adds values in setting of diagnostic CT and delays intervention

Transesophageal echocardiography (TEE)

•Highly accurate•Can be performed at beside or OR, or those who cannot tolerate contrast•Limited to proximal ruptures, operator dependent•Largely replaced by MDCT

Magnetic Resonance (MR)

•Limited by accessibility, scan time•Potential role in follow-up after post-op aortic repair or equivocal findings•Strategy for radiation dose reduction in young trauma victims

Adapted from Legome, E. Uptodate, 2010

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.

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

Mirvis SE, Shanmuganathan K. Eur J Radiol. 2007 Oct;64(1):27-40. Epub 2007 Mar 21.

Demetriades D, et al. J Trauma. 2008 Jun;64(6):1415-8.

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


ProtocolmAs(Tube A) kV 120

Kernel B Kernel B Kernel B Kernel B Collimation Pitch Rot Time CTDI vol

Aortic Dissection (scan time 7 sec)

240

B43(Mediastinum)

Axial 1mmx0.9mm

B60(Lung)Axial

5mmx2.5mm

B43(Mediastinum)Oblique Arch 3mmx1mm

MIP

B43(Mediastinum)

Coronal 3mmx1.5mm

128 mmx 0.6mm

0.6 0.33sec 16.22mGy

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.

Presley Classification: Grade 1

Grade 1a:- Normal aorta- NO mediastinal hematoma

Grade 1b:- Normal aorta- mediastinal hematoma, aorta surrounded by fatplane


Grade 2a:- Psuedoaneurysm, intimal flap or thrombus < 1cm- NO mediastinal hematoma

Grade 2b:- Psuedoaneurysm, intimal flap or thrombus < 1cm- Peri-aortic hematoma




Grade 3a:- regular pseudoaneurysm > 1 cm with intimal flap or thrombus- peri-aortic hematoma- NO involvement 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



Grade 4:- Irregular, poorly defined Pseudoaneurysm with intimal flap or thrombus- large peri-aortic hematoma


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


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)

Presley 2B

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

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


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)

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


Presley 3B

*

*

•Pseudoaneurysm of the distal aortic arch (yellow arrow)•Peri-aortic extensive mediastinal hematoma (blue arrows)•Asterisks indicate aortic lumen of the arch

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


Presley 4

A B

*

C D

*

**

•Irregular pseudoaneurysm (asterisks) •Active extravasation (blue arrows)•Native aortic lumen is narrowed (yellow arrows)

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


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)

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)

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)

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



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.

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.

50 yo male MVC, unbelted driver

Out pouching from inferior margin of aortic arch concavity posteriorly 1 cm in lengthSignificant mediastinal hematoma within anterior superior mediastinum

Forbes J, et al. Eur J Radiol. 2010 In Press

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


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



MRI follow-up of Stent graft repair

CT follow-up after stent graft repairMRI follow-up 1 year after stent graft repair

Imaging follow-up post-repair

Focal aneurysm seen is a focal expansion of the stent

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

ProtocolmAs(Tube A)

kV 120Kernel B Kernel B Kernel B Collimation Pitch Rot Time CTDI vol

FLASH Aortic Dissection (scan time 0.6 sec)

210B36

(Mediastinum)Axial 2mmx1mm

B70(Lung)Axial

1mmx1mm

B36(Mediastinum)

Coronal 3mmx1mm

128 mmx 0.6mm 3.2 0.28s 9.08mGy

Screening for BTAI

CXR

Abnormal mediastinum

CT with contrast

Normal CT

No further action

BTAI

Treatment

Equivocal finding

Gated Study or MRI

Normal mediastinum

Suspicious Hx

No further action

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

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


Fabian TC, et al. Ann Surg. 1998 May;227(5):666-76.Demetriades D, et al. J Trauma. 2008 Jun;64(6):1415-8.

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

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

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. Radiol Clin 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 Vasc Endovasc 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.

mdct and mri pictorial review of blunt traumatic aortic injury

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