MDCT AND MRI Pictorial review of Blunt traumatic aortic injury

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15 Νοε 2013 (πριν από 3 χρόνια και 7 μήνες)

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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

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




s
uspect 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









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.

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
pressure

Berger 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 Options

Imaging Modality

Comments

Plain radiograph


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moderate suspicion


If high clinical suspicion, or abnormal radiograph, further testing required

Chest

CT Scan


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Transesophageal
echocardiography

(TEE)


Highly

accurate


Can be performed at beside or OR, or those who cannot tolerate contrast


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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

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

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

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

Protocol

mAs
(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

Gavant ML. Radiol Clin North Am. 1999 May;37(3):553
-
74, vi.

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.

Presley Classification: Grade 2

Gavant ML. Radiol Clin North Am. 1999 May;37(3):553
-
74, vi.

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

Presley Classification: Grade 3

Gavant ML. Radiol Clin North Am. 1999 May;37(3):553
-
74, vi.

Grade 4:

-

Irregular
, poorly defined


Pseudoaneurysm with intimal flap or
thrombus

-

large peri
-
aortic hematoma

Presley Classification: Grade 4

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.

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


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

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

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

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.

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

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

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



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

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

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 length

Significant 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

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

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



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

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

MRI follow
-
up of Stent graft
repair

CT follow
-
up after stent graft repair

MRI 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

Protocol

mAs(Tube A)
kV 120

Kernel B

Kernel B

Kernel B

Collimation

Pitch

Rot Time

CTDI vol

FLASH
Aortic

Dissection
(scan
time

0.6
sec)



210

B36

(
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

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

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.